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NeoPixel Playground


The NeoPixel Digital RGB LED Strip (144 LED/m) is a really impressive product that will have you lighting up your room in next to no time. The 144 individually addressable LEDs packed onto a 1 metre flexible water resistant strip, enables a world of luminescent creativity that will blow your blinking Arduino friends away. The following tutorial will show you how to create an immersive and interactive LED display using an Arduino UNO, a potentiometer and an accelerometer. There will be a total of FIVE LED sequences to keep you entertained or you can create your own !
 
This tutorial was specifically designed to work with the 144 Neopixel Digital RGB LED strip with the ws2812B chipset.

 

Parts Required:

Power Requirements

Before you start any LED strip project, the first thing you will need to think about is POWER. According to the Adafruit website, each individual NeoPixel LED can draw up to 60 milliamps at maximum brightness - white. Therefore the amount of current required for the entire strip will be way more than your Arduino can handle. If you try to power this LED strip directly from your Arduino, you run the risk of damaging not only your Arduino, but your USB port as well. The Arduino will be used to control the LED strip, but the LED strip will need to be powered by a separate power supply. The power supply you choose to use is important. It must provide the correct voltage, and must able to supply sufficient current.
 

Operating Voltage(5V)

The operating voltage of the NeoPixel strip is 5 volts DC. Excessive voltage will damage/destroy your NeoPixels.

Current requirements (8.6 Amps)

OpenLab recommend the use of a 5V 10A power supply. Having more Amps is OK, providing the output voltage is 5V DC. The LEDs will only draw as much current as they need. To calculate the amount of current this 1m strip can draw with all LEDs turned on at full brightness - white:

144 NeoPixel LEDs x 60 mA x 1 m = 8640 mA = 8.64 Amps for a 1 metre strip.

Therefore a 5V 10A power supply would be able to handle the maximum current (8.6 Amps) demanded by a single 1m NeoPixel strip of 144 LEDs.
 
 

Arduino Libraries and IDE


Before you start to hook up any components, upload the following sketch to the Arduino microcontroller. I am assuming that you already have the Arduino IDE installed on your computer. If not, the IDE can be downloaded from here.
 
The FastLED library is useful for simplifying the code for programming the NeoPixels. The latest "FastLED library" can be downloaded from here. I used FastLED library version 3.0.3 in this project.
 
If you have a different LED strip or your NeoPixels have a different chipset, make sure to change the relevant lines of code to accomodate your hardware. I would suggest you try out a few of the FastLED library examples before using the code below, so that you become more familiar with the library, and will be better equipped to make the necessary changes. If you have a single 144 NeoPixel LED/m strip with the ws2812B chipset, then you will not have to make any modifications below (unless you want to).
 

ARDUINO CODE:


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/* ==================================================================================================================================================
         Project: NeoPixel Playground
Neopixel chipset: ws2812B  (144 LED/m strip)
          Author: Scott C
         Created: 12th June 2015
     Arduino IDE: 1.6.4
         Website: http://arduinobasics.blogspot.com/p/arduino-basics-projects-page.html
     Description: This project will allow you to cycle through and control five LED
                  animation sequences using a potentiometer and an accelerometer
                     Sequence 1:   Cylon with Hue Control                                       Control: Potentiometer only
                     Sequence 2:   Cylon with Brightness Control                                Control: Potentiometer only
                     Sequence 3:   Comet effect with Hue and direction control                  Control: Potentiometer and Accelerometer (Y axis only)
                     Sequence 4:   FireStarter / Rainbow effect with Hue and Direction control  Control: Potentiometer and Accelerometer (Y axis only)
                     Sequence 5:   Digital Spirit Level                                         Control: Accelerometer only (Y axis)
            
                  This project makes use of the FastLED library. Some of the code below was adapted from the FastLED library examples (eg. Cylon routine).
                  The Comet, FireStarter and Digital Spirit Level sequence was designed by ScottC.
                  The FastLED library can be found here: http://fastled.io/
                  You may need to modify the code below to accomodate your specific LED strip. See the FastLED library site for more details.
===================================================================================================================================================== */

//This project needs the FastLED library - link in the description.
#include "FastLED.h"

//The total number of LEDs being used is 144
#define NUM_LEDS 144

// The data pin for the NeoPixel strip is connected to digital Pin 6 on the Arduino
#define DATA_PIN 6

//Initialise the LED array, the LED Hue (ledh) array, and the LED Brightness (ledb) array.
CRGB leds[NUM_LEDS];
byte ledh[NUM_LEDS];
byte ledb[NUM_LEDS];

//Pin connections
const int potPin = A0; // The potentiometer signal pin is connected to Arduino's Analog Pin 0
const int yPin = A4; // Y pin on accelerometer is connected to Arduino's Analog Pin 4
                            // The accelerometer's X Pin and the Z Pin were not used in this sketch

//Global Variables ---------------------------------------------------------------------------------
byte potVal; // potVal: stores the potentiometer signal value
byte prevPotVal=0; // prevPotVal: stores the previous potentiometer value
int LEDSpeed=1; // LEDSpeed: stores the "speed" of the LED animation sequence
int maxLEDSpeed = 50; // maxLEDSpeed: identifies the maximum speed of the LED animation sequence
int LEDAccel=0; // LEDAccel: stores the acceleration value of the LED animation sequence (to speed it up or slow it down)
int LEDPosition=72; // LEDPosition: identifies the LED within the strip to modify (leading LED). The number will be between 0-143. (Zero to NUM_LEDS-1)
int oldPos=0; // oldPos: holds the previous position of the leading LED
byte hue = 0; // hue: stores the leading LED's hue value
byte intensity = 150; // intensity: the default brightness of the leading LED
byte bright = 80; // bright: this variable is used to modify the brightness of the trailing LEDs
int animationDelay = 0; // animationDelay: is used in the animation Speed calculation. The greater the animationDelay, the slower the LED sequence.
int effect = 0; // effect: is used to differentiate and select one out of the four effects
int sparkTest = 0; // sparkTest: variable used in the "sparkle" LED animation sequence
boolean constSpeed = false; // constSpeed: toggle between constant and variable speed.


//===================================================================================================================================================
// setup() : Is used to initialise the LED strip
//===================================================================================================================================================
void setup() {
    delay(2000); //Delay for two seconds to power the LEDS before starting the data signal on the Arduino
    FastLED.addLeds<WS2812B, DATA_PIN, GRB>(leds, NUM_LEDS); //initialise the LED strip
}


//===================================================================================================================================================
// loop() : The Arduino will take readings from the potentiometer and accelerometer to control the LED strip
//===================================================================================================================================================
void loop(){
  readPotentiometer();           
  adjustSpeed();
  constrainLEDs();
 
  switch(effect){
    case 0: // 1st effect : Cylon with Hue control - using Potentiometer
      cylonWithHueControl();
      break;
      
    case 1: // 2nd effect : Cylon with Brightness control - using Potentiometer
      cylonWithBrightnessControl();
      break;
      
    case 2: // 3rd effect : Comet effect. Hue controlled by potentiometer, direction by accelerometer
      cometEffect();
      break;
      
    case 3: // 4th effect : FireStarter / Rainbow Sparkle effect. Direction controlled by accelerometer, sparkle by potentiometer.
      fireStarter(); 
      break;
    
    case 4:
      levelSense();                                        // 5th effect : LevelSense - uses the accelerometer to create a digital "spirit" level.
      break;
  }
}


//===================================================================================================================================================
// readPotentiometer() : Take a potentiometer reading. This value will be used to control various LED animations, and to choose the animation sequence to display.
//===================================================================================================================================================
void readPotentiometer(){
  //Take a reading from the potentiometer and convert the value into a number between 0 and 255
  potVal = map(analogRead(potPin), 0, 1023 , 0, 255);
  
  // If the potentiometer reading is equal to zero, then move to the next effect in the list.
  if(potVal==0){
    if(prevPotVal>0){ // This allows us to switch effects only when the potentiometer reading has changed to zero (from a positive number). Multiple zero readings will be ignored.
      prevPotVal = 0;   // Set the prev pot value to zero in order to ignore replicate zero readings.
      effect++;         // Go to the next effect.
      if(effect>4){
        effect=0;       // Go back to the first effect after the fifth effect.
      }
    }
  }
  prevPotVal=potVal;    // Keep track of the previous potentiometer reading
}


//===================================================================================================================================================
// adjustSpeed() : use the Y axis value of the accelerometer to adjust the speed and the direction of the LED animation sequence
//===================================================================================================================================================
void adjustSpeed(){
  // Take a reading from the Y Pin of the accelerometer and adjust the value so that
  // positive numbers move in one direction, and negative numbers move in the opposite diraction.
  // We use the map function to convert the accelerometer readings, and the constrain function to ensure that it stays within the desired limits
  // The values of 230 and 640 were determined by trial and error and are specific to my accelerometer. You will need to adjust these numbers to suit your module.
  
  LEDAccel = constrain(map(analogRead(yPin), 230, 640 , maxLEDSpeed, -maxLEDSpeed),-maxLEDSpeed, maxLEDSpeed);
  
  
  // If the constSpeed variable is "true", then make sure that the speed of the animation is constant by modifying the LEDSpeed and LEDAccel variables.
  if(constSpeed){
    LEDAccel=0; 
    if(LEDSpeed>0){
      LEDSpeed = maxLEDSpeed/1.1;     // Adjust the LEDSpeed to half the maximum speed in the positive direction
    } 
    if (LEDSpeed<0){
      LEDSpeed = -maxLEDSpeed/1.1;    // Adjust the LEDSpeed to half the maximum speed in the negative direction
    }
  } 
 
  // The Speed of the LED animation sequence can increase (accelerate), decrease (decelerate) or stay the same (constant speed)
  LEDSpeed = LEDSpeed + LEDAccel;                        
  
  //The following lines of code are used to control the direction of the LED animation sequence, and limit the speed of that animation.
  if (LEDSpeed>0){
    LEDPosition++;                                       // Illuminate the LED in the Next position
    if (LEDSpeed>maxLEDSpeed){
      LEDSpeed=maxLEDSpeed;                              // Ensure that the speed does not go beyond the maximum speed in the positive direction
    }
  }
  
  if (LEDSpeed<0){
    LEDPosition--;                                       // Illuminate the LED in the Prior position
    if (LEDSpeed<-maxLEDSpeed){
      LEDSpeed = -maxLEDSpeed;                           // Ensure that the speed does not go beyond the maximum speed in the negative direction
    }
  }
}


//===================================================================================================================================================
// constrainLEDs() : This ensures that the LED animation sequence remains within the boundaries of the various arrays (and the LED strip)
//                   and it also creates a "bouncing" effect at both ends of the LED strip.
//===================================================================================================================================================
void constrainLEDs(){
  LEDPosition = constrain(LEDPosition, 0, NUM_LEDS-1); // Make sure that the LEDs stay within the boundaries of the LED strip
  if(LEDPosition == 0 || LEDPosition == NUM_LEDS-1) {
    LEDSpeed = (LEDSpeed * -0.9);                         // Reverse the direction of movement when LED gets to end of strip. This creates a bouncing ball effect.
  }
}



//===================================================================================================================================================
// cylonWithHueControl() :  This is the 1st LED effect. The cylon colour is controlled by the potentiometer. The speed is constant.
//===================================================================================================================================================
void cylonWithHueControl(){
      constSpeed = true; // Make the LED animation speed constant
      showLED(LEDPosition, potVal, 255, intensity);       // Illuminate the LED
      fadeLEDs(8);                                        // Fade LEDs by a value of 8. Higher numbers will create a shorter tail.
      setDelay(LEDSpeed);                                 // The LEDSpeed is constant, so the delay is constant
}


//===================================================================================================================================================
// cylonWithBrightnessControl() : This is the 2nd LED effect. The cylon colour is red (hue=0), and the brightness is controlled by the potentiometer
//===================================================================================================================================================
void cylonWithBrightnessControl(){
      constSpeed = true; // Make speed constant
      showLED(LEDPosition, 0, 255, potVal);               // Brightness is controlled by potentiometer.
      fadeLEDs(16);                                       // Fade LEDs by a value of 16
      setDelay(LEDSpeed);                                 // The LEDSpeed is constant, so the delay is constant
}


//===================================================================================================================================================
// cometEffect() :  This is the 3rd LED effect. The random brightness of the trailing LEDs produces an interesting comet-like effect.
//===================================================================================================================================================
void cometEffect(){
      constSpeed = false; // The speed will be controlled by the slope of the accelerometer (y-Axis)
      showLED(LEDPosition, potVal, 255, intensity);        // Hue will change with potentiometer.
      
      //The following lines create the comet effect
      bright = random(50, 100); // Randomly select a brightness between 50 and 100
      leds[LEDPosition] = CHSV((potVal+40),255, bright); // The trailing LEDs will have a different hue to the leading LED, and will have a random brightness
      fadeLEDs(8);                                         // This will affect the length of the Trailing LEDs
      setDelay(LEDSpeed);                                  // The LEDSpeed will be affected by the slope of the Accelerometer's y-Axis
}


//===================================================================================================================================================
// fireStarter() : This is the 4th LED effect. It starts off looking like a ball of fire, leaving a trail of little fires. But as you
//                 turn the potentiometer, it becomes more like a shooting star with a rainbow-sparkle trail.
//===================================================================================================================================================
void fireStarter(){
      constSpeed = false; // The speed will be controlled by the slope of the accelerometer (y-Axis)
      ledh[LEDPosition] = potVal;                          // Hue is controlled by potentiometer
      showLED(LEDPosition, ledh[LEDPosition], 255, intensity); 
      
      //The following lines create the fire starter effect
      bright = random(50, 100); // Randomly select a brightness between 50 and 100
      ledb[LEDPosition] = bright;                          // Assign this random brightness value to the trailing LEDs
      sparkle(potVal/5);                                   // Call the sparkle routine to create that sparkling effect. The potentiometer controls the difference in hue from LED to LED.
      fadeLEDs(1);                                         // A low number creates a longer tail
      setDelay(LEDSpeed);                                  // The LEDSpeed will be affected by the slope of the Accelerometer's y-Axis
}


//===================================================================================================================================================
// levelSense() : This is the 5th and final LED effect. The accelerometer is used in conjunction with the LED strip to create a digital "Spirit" Level.
//                You can use the illuminated LEDs to identify the angle of the LED strip
//===================================================================================================================================================
void levelSense(){
      constSpeed = true;
      LEDPosition = constrain(map(analogRead(yPin), 230, 640, 1, NUM_LEDS-1), 0 , NUM_LEDS-1);
      
      //Jitter correction: this will reduce the amount of jitter caused by the accelerometer reading variability
      if(abs(LEDPosition-oldPos) < 2){
        LEDPosition = oldPos;
      }
      
      //The following lines of code will ensure the colours remain within the red to green range, with green in the middle and red at the ends.
      hue = map(LEDPosition, 0, NUM_LEDS-1, 0, 200);
      if (hue>100){
         hue = 200 - hue;
      }
      
      //Illuminate 2 LEDs next to each other
      showLED(LEDPosition, hue, 255, intensity); 
      showLED(LEDPosition-1, hue, 255, intensity);              
      
      //If the position moves, then fade the old LED positions by a factor of 25 (high numbers mean shorter tail)
      fadeLEDs(25);                               
      oldPos = LEDPosition; 
}


//===================================================================================================================================================
// fadeLEDs(): This function is used to fade the LEDs back to black (OFF) 
//===================================================================================================================================================
void fadeLEDs(int fadeVal){
  for (int i = 0; i<NUM_LEDS; i++){
    leds[i].fadeToBlackBy( fadeVal );
  }
}



//===================================================================================================================================================
// showLED() : is used to illuminate the LEDs 
//===================================================================================================================================================
void showLED(int pos, byte LEDhue, byte LEDsat, byte LEDbright){
  leds[pos] = CHSV(LEDhue,LEDsat,LEDbright);
  FastLED.show();
}


//===================================================================================================================================================
// setDelay() : is where the speed of the LED animation sequence is controlled. The speed of the animation is controlled by the LEDSpeed variable.
//              and cannot go faster than the maxLEDSpeed variable.
//===================================================================================================================================================
void setDelay(int LSpeed){
  animationDelay = maxLEDSpeed - abs(LSpeed);
  delay(animationDelay);
}


//===================================================================================================================================================
// sparkle() : is used by the fireStarter routine to create a sparkling/fire-like effect
//             Each LED hue and brightness is monitored and modified using arrays  (ledh[]  and ledb[])
//===================================================================================================================================================
void sparkle(byte hDiff){
  for(int i = 0; i < NUM_LEDS; i++) {
    ledh[i] = ledh[i] + hDiff;                // hDiff controls the extent to which the hue changes along the trailing LEDs
    
    // This will prevent "negative" brightness.
    if(ledb[i]<3){
      ledb[i]=0;
    }
    
    // The probability of "re-igniting" an LED will decrease as you move along the tail
    // Once the brightness reaches zero, it cannot be re-ignited unless the leading LED passes over it again.
    if(ledb[i]>0){
      ledb[i]=ledb[i]-2;
      sparkTest = random(0,bright);
      if(sparkTest>(bright-(ledb[i]/1.1))){
        ledb[i] = bright;
      } else {
        ledb[i] = ledb[i] / 2;                  
      }
    }
    leds[i] = CHSV(ledh[i],255,ledb[i]);
  }
}


 

NeoPixel Strip connection

The NeoPixel strip is rolled up when you first get it. You will notice that there are wires on both sides of the strip. This allows you to chain LED strips together to make longer strips. The more LEDs you have, the more current you will need. Connect your Arduino and power supply to the left side of the strip, with the arrows pointing to the right side of the strip.
 

Follow the Arrows

The arrows are quite hard to see on this particular LED strip because they are so small, plus they are located right under the thicker part of the NeoPixel weatherproof sheath. I have circled the arrows in RED so that you know where to look:

 


NeoPixel Strip Wires

There are 4 wires coming from either side of the NeoPixel LED strip:
 
  One red wire, one white wire, and two black wires.
 
It doesn't matter which Black wire you use to connect to the power supply (or Arduino) GND. Both black wires appear to be going to the same pin on the LED strip anyway. Use the table below to make the necessary NeoPixel Strip connections to the Arduino and power supply.


Large Capacitor

Adafruit also recommend the use of a large capacitor across the + and - terminals of the LED strip to "prevent the initial onrush of current from damaging the pixels". Adafruit recommends a capacitor that is 1000uF, 6.3V or higher. I used a 4700uF 16V Electrolytic Capacitor.

Resistor on Data Pin

Another recommendation from Adafruit is to place a "300 to 500 Ohm resistor" between the Arduino's data pin and the data input on the first NeoPixel to prevent voltage spikes that can damage the first pixel. I used a 330 Ohm resistor.
 

Powering your Arduino (USB vs Power supply)

You can power your Arduino board via USB cable or via the LED strip power supply.
*** Please note: different power supplies will yield different accelerometer readings. I noticed this when changing the Arduino's power source from USB to LED power supply. My final sketch was designed to eliminate the USB/computer connection, hence I have chosen to power the Arduino via the power supply. The fritzing sketch below shows the Arduino being powered by a power supply only.

**WARNING: If you decide to power your Arduino UNO via a USB cable, please make sure to remove (or disconnect) the wire that goes to the the Arduino VIN pin. The GND connections remain unchanged.


Fritzing Sketch - NeoPixel strip connection


 

Potentiometer connection

The potentiometer will be used to switch between the different LED sequences. When it reads zero, it will switch to the next sequence in the list. It will jump right back to the beginning after the last sequence. The potentiometer is also used to interact with the LEDs (e.g. controlling hue, brightness etc etc).
See the fritzing sketch below to add the potentiometer to this project.



 

Accelerometer connection (Y-axis)

The accelerometer makes the LEDs much more fun and interactive. We will only be using the Y-axis of the accelerometer in this sketch. By tilting the accelerometer from one side to the other, the LEDs react and respond accordingly. The accelerometer is an essential component of the digital spirit level sequence. That's right ! You can use this sketch to create your own spirit level. This digital version can also be used to measure angles !
 
Have a look below to see how to hook up the accelerometer to the Arduino. The Y-axis is connected to the Arduino analog pin 4. If you wanted to use the X and Z axis, connect them to one of the other available analog pins (eg. A3 and A5).




 

Let the fun begin !!

Now that you have the Arduino code uploaded to the Arduino, and have made all of the necessary wire/component connections, it is time to turn on the power supply.
 

Sequence 1: Cylon with Hue control

The LEDs will move from one end of the strip to the other. It should start off as a RED cylon effect. As you turn the potentiometer clockwise, the colour of the LEDs will change and move through the various colours of the rainbow. If the potentiometer reading gets back to zero (fully anti-clockwise), it will move to sequence 2.
 

Sequence 2: Cylon with brightness control

You will see that the LEDs have turned off. The potentiometer readings correlate with the LED brightness. At the start of this sequence, the potentiometer readings will be zero, therefore the brightness will be zero (LEDs turned off). As you turn the potentiometer clockwise, the readings increase, and so will the brightness of the LEDs.
 

Sequence 3: Comet effect with Hue and direction control

This is where the real fun begins. You control the hue of the leading LED with the potentiometer, however the LED will move along the LED strip as though it were affected by gravity. As it hits the end of the LED strip, it will bounce for a while and eventually come to a stop. The more you tilt the accelerometer, the greater the acceleration of the leading LED. The trailing LEDs have an interesting randomised glow, which creates the "comet" effect.
 

Sequence 4: FireStarter / Rainbow effect : Hue and direction control

The initial colours of LEDs in this sequence creates a fire-like animation. As the leading LED moves along the LED strip, it appears to ignite the LEDs in its path, leaving a fire trail behind it. The fire effect is best when you turn the potentiometer clockwise slightly to introduce a small amount of yellow into the mix of colours. As you turn the potentiometer further clockwise, the fire trail turns into a pretty rainbow trail. The accelerometer affects the leading LED in the same way as the previous sequence.
 

Sequence 5: Digital spirit level

This sequence was my original idea for this project, however I thought it would be nice to share some of the other cool effects I created on my journey of discovery. The idea was to make a digital version of a spirit level. I originally wanted the LEDs to represent a spirit level bubble that would "float" according to the vertical/horizontal position of the LED strip. However, as I played around with this sketch, I discovered that it could potentially be used to measure the angle of the strip relative to the horizon. The angle can be determined by the illuminated LED. If the strip is horizontal, the illuminated LEDs will be close to the middle of the strip, and their colour will be green. If the strip is vertical, the illuminated LEDs will be close to end of the strip, and their colour will be red. The colour is just an additional visual indicator.
 


Concluding Comments

The NeoPixel Digital RGB LED strip is a lot of fun. The FastLED library makes for easy programming, and allows you to get up and running really quickly. 144 LEDs on a single strip means you have plenty of room for creative algorithms and lighting effects. Add a few sensors, and "pretty" quickly turns into "awesome" !!
 
This tutorial shows you how to control a "144 NeoPixel per metre Digital RGB LED strip" with an Arduino UNO. Feel free to share your own LED creations in the comments below.



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NeoPixel Playground


The NeoPixel Digital RGB LED Strip (144 LED/m) is a really impressive product that will have you lighting up your room in next to no time. The 144 individually addressable LEDs packed onto a 1 metre flexible water resistant strip, enables a world of luminescent creativity that will blow your blinking Arduino friends away. The following tutorial will show you how to create an immersive and interactive LED display using an Arduino UNO, a potentiometer and an accelerometer. There will be a total of FIVE LED sequences to keep you entertained or you can create your own !
 
This tutorial was specifically designed to work with the 144 Neopixel Digital RGB LED strip with the ws2812B chipset.

 

Parts Required:

Power Requirements

Before you start any LED strip project, the first thing you will need to think about is POWER. According to the Adafruit website, each individual NeoPixel LED can draw up to 60 milliamps at maximum brightness - white. Therefore the amount of current required for the entire strip will be way more than your Arduino can handle. If you try to power this LED strip directly from your Arduino, you run the risk of damaging not only your Arduino, but your USB port as well. The Arduino will be used to control the LED strip, but the LED strip will need to be powered by a separate power supply. The power supply you choose to use is important. It must provide the correct voltage, and must able to supply sufficient current.
 

Operating Voltage(5V)

The operating voltage of the NeoPixel strip is 5 volts DC. Excessive voltage will damage/destroy your NeoPixels.

Current requirements (8.6 Amps)

OpenLab recommend the use of a 5V 10A power supply. Having more Amps is OK, providing the output voltage is 5V DC. The LEDs will only draw as much current as they need. To calculate the amount of current this 1m strip can draw with all LEDs turned on at full brightness - white:

144 NeoPixel LEDs x 60 mA x 1 m = 8640 mA = 8.64 Amps for a 1 metre strip.

Therefore a 5V 10A power supply would be able to handle the maximum current (8.6 Amps) demanded by a single 1m NeoPixel strip of 144 LEDs.
 
 

Arduino Libraries and IDE


Before you start to hook up any components, upload the following sketch to the Arduino microcontroller. I am assuming that you already have the Arduino IDE installed on your computer. If not, the IDE can be downloaded from here.
 
The FastLED library is useful for simplifying the code for programming the NeoPixels. The latest "FastLED library" can be downloaded from here. I used FastLED library version 3.0.3 in this project.
 
If you have a different LED strip or your NeoPixels have a different chipset, make sure to change the relevant lines of code to accomodate your hardware. I would suggest you try out a few of the FastLED library examples before using the code below, so that you become more familiar with the library, and will be better equipped to make the necessary changes. If you have a single 144 NeoPixel LED/m strip with the ws2812B chipset, then you will not have to make any modifications below (unless you want to).
 

ARDUINO CODE:


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/* ==================================================================================================================================================
         Project: NeoPixel Playground
Neopixel chipset: ws2812B  (144 LED/m strip)
          Author: Scott C
         Created: 12th June 2015
     Arduino IDE: 1.6.4
         Website: http://arduinobasics.blogspot.com/p/arduino-basics-projects-page.html
     Description: This project will allow you to cycle through and control five LED
                  animation sequences using a potentiometer and an accelerometer
                     Sequence 1:   Cylon with Hue Control                                       Control: Potentiometer only
                     Sequence 2:   Cylon with Brightness Control                                Control: Potentiometer only
                     Sequence 3:   Comet effect with Hue and direction control                  Control: Potentiometer and Accelerometer (Y axis only)
                     Sequence 4:   FireStarter / Rainbow effect with Hue and Direction control  Control: Potentiometer and Accelerometer (Y axis only)
                     Sequence 5:   Digital Spirit Level                                         Control: Accelerometer only (Y axis)
            
                  This project makes use of the FastLED library. Some of the code below was adapted from the FastLED library examples (eg. Cylon routine).
                  The Comet, FireStarter and Digital Spirit Level sequence was designed by ScottC.
                  The FastLED library can be found here: http://fastled.io/
                  You may need to modify the code below to accomodate your specific LED strip. See the FastLED library site for more details.
===================================================================================================================================================== */

//This project needs the FastLED library - link in the description.
#include "FastLED.h"

//The total number of LEDs being used is 144
#define NUM_LEDS 144

// The data pin for the NeoPixel strip is connected to digital Pin 6 on the Arduino
#define DATA_PIN 6

//Initialise the LED array, the LED Hue (ledh) array, and the LED Brightness (ledb) array.
CRGB leds[NUM_LEDS];
byte ledh[NUM_LEDS];
byte ledb[NUM_LEDS];

//Pin connections
const int potPin = A0; // The potentiometer signal pin is connected to Arduino's Analog Pin 0
const int yPin = A4; // Y pin on accelerometer is connected to Arduino's Analog Pin 4
                            // The accelerometer's X Pin and the Z Pin were not used in this sketch

//Global Variables ---------------------------------------------------------------------------------
byte potVal; // potVal: stores the potentiometer signal value
byte prevPotVal=0; // prevPotVal: stores the previous potentiometer value
int LEDSpeed=1; // LEDSpeed: stores the "speed" of the LED animation sequence
int maxLEDSpeed = 50; // maxLEDSpeed: identifies the maximum speed of the LED animation sequence
int LEDAccel=0; // LEDAccel: stores the acceleration value of the LED animation sequence (to speed it up or slow it down)
int LEDPosition=72; // LEDPosition: identifies the LED within the strip to modify (leading LED). The number will be between 0-143. (Zero to NUM_LEDS-1)
int oldPos=0; // oldPos: holds the previous position of the leading LED
byte hue = 0; // hue: stores the leading LED's hue value
byte intensity = 150; // intensity: the default brightness of the leading LED
byte bright = 80; // bright: this variable is used to modify the brightness of the trailing LEDs
int animationDelay = 0; // animationDelay: is used in the animation Speed calculation. The greater the animationDelay, the slower the LED sequence.
int effect = 0; // effect: is used to differentiate and select one out of the four effects
int sparkTest = 0; // sparkTest: variable used in the "sparkle" LED animation sequence
boolean constSpeed = false; // constSpeed: toggle between constant and variable speed.


//===================================================================================================================================================
// setup() : Is used to initialise the LED strip
//===================================================================================================================================================
void setup() {
    delay(2000); //Delay for two seconds to power the LEDS before starting the data signal on the Arduino
    FastLED.addLeds<WS2812B, DATA_PIN, GRB>(leds, NUM_LEDS); //initialise the LED strip
}


//===================================================================================================================================================
// loop() : The Arduino will take readings from the potentiometer and accelerometer to control the LED strip
//===================================================================================================================================================
void loop(){
  readPotentiometer();           
  adjustSpeed();
  constrainLEDs();
 
  switch(effect){
    case 0: // 1st effect : Cylon with Hue control - using Potentiometer
      cylonWithHueControl();
      break;
      
    case 1: // 2nd effect : Cylon with Brightness control - using Potentiometer
      cylonWithBrightnessControl();
      break;
      
    case 2: // 3rd effect : Comet effect. Hue controlled by potentiometer, direction by accelerometer
      cometEffect();
      break;
      
    case 3: // 4th effect : FireStarter / Rainbow Sparkle effect. Direction controlled by accelerometer, sparkle by potentiometer.
      fireStarter(); 
      break;
    
    case 4:
      levelSense();                                        // 5th effect : LevelSense - uses the accelerometer to create a digital "spirit" level.
      break;
  }
}


//===================================================================================================================================================
// readPotentiometer() : Take a potentiometer reading. This value will be used to control various LED animations, and to choose the animation sequence to display.
//===================================================================================================================================================
void readPotentiometer(){
  //Take a reading from the potentiometer and convert the value into a number between 0 and 255
  potVal = map(analogRead(potPin), 0, 1023 , 0, 255);
  
  // If the potentiometer reading is equal to zero, then move to the next effect in the list.
  if(potVal==0){
    if(prevPotVal>0){ // This allows us to switch effects only when the potentiometer reading has changed to zero (from a positive number). Multiple zero readings will be ignored.
      prevPotVal = 0;   // Set the prev pot value to zero in order to ignore replicate zero readings.
      effect++;         // Go to the next effect.
      if(effect>4){
        effect=0;       // Go back to the first effect after the fifth effect.
      }
    }
  }
  prevPotVal=potVal;    // Keep track of the previous potentiometer reading
}


//===================================================================================================================================================
// adjustSpeed() : use the Y axis value of the accelerometer to adjust the speed and the direction of the LED animation sequence
//===================================================================================================================================================
void adjustSpeed(){
  // Take a reading from the Y Pin of the accelerometer and adjust the value so that
  // positive numbers move in one direction, and negative numbers move in the opposite diraction.
  // We use the map function to convert the accelerometer readings, and the constrain function to ensure that it stays within the desired limits
  // The values of 230 and 640 were determined by trial and error and are specific to my accelerometer. You will need to adjust these numbers to suit your module.
  
  LEDAccel = constrain(map(analogRead(yPin), 230, 640 , maxLEDSpeed, -maxLEDSpeed),-maxLEDSpeed, maxLEDSpeed);
  
  
  // If the constSpeed variable is "true", then make sure that the speed of the animation is constant by modifying the LEDSpeed and LEDAccel variables.
  if(constSpeed){
    LEDAccel=0; 
    if(LEDSpeed>0){
      LEDSpeed = maxLEDSpeed/1.1;     // Adjust the LEDSpeed to half the maximum speed in the positive direction
    } 
    if (LEDSpeed<0){
      LEDSpeed = -maxLEDSpeed/1.1;    // Adjust the LEDSpeed to half the maximum speed in the negative direction
    }
  } 
 
  // The Speed of the LED animation sequence can increase (accelerate), decrease (decelerate) or stay the same (constant speed)
  LEDSpeed = LEDSpeed + LEDAccel;                        
  
  //The following lines of code are used to control the direction of the LED animation sequence, and limit the speed of that animation.
  if (LEDSpeed>0){
    LEDPosition++;                                       // Illuminate the LED in the Next position
    if (LEDSpeed>maxLEDSpeed){
      LEDSpeed=maxLEDSpeed;                              // Ensure that the speed does not go beyond the maximum speed in the positive direction
    }
  }
  
  if (LEDSpeed<0){
    LEDPosition--;                                       // Illuminate the LED in the Prior position
    if (LEDSpeed<-maxLEDSpeed){
      LEDSpeed = -maxLEDSpeed;                           // Ensure that the speed does not go beyond the maximum speed in the negative direction
    }
  }
}


//===================================================================================================================================================
// constrainLEDs() : This ensures that the LED animation sequence remains within the boundaries of the various arrays (and the LED strip)
//                   and it also creates a "bouncing" effect at both ends of the LED strip.
//===================================================================================================================================================
void constrainLEDs(){
  LEDPosition = constrain(LEDPosition, 0, NUM_LEDS-1); // Make sure that the LEDs stay within the boundaries of the LED strip
  if(LEDPosition == 0 || LEDPosition == NUM_LEDS-1) {
    LEDSpeed = (LEDSpeed * -0.9);                         // Reverse the direction of movement when LED gets to end of strip. This creates a bouncing ball effect.
  }
}



//===================================================================================================================================================
// cylonWithHueControl() :  This is the 1st LED effect. The cylon colour is controlled by the potentiometer. The speed is constant.
//===================================================================================================================================================
void cylonWithHueControl(){
      constSpeed = true; // Make the LED animation speed constant
      showLED(LEDPosition, potVal, 255, intensity);       // Illuminate the LED
      fadeLEDs(8);                                        // Fade LEDs by a value of 8. Higher numbers will create a shorter tail.
      setDelay(LEDSpeed);                                 // The LEDSpeed is constant, so the delay is constant
}


//===================================================================================================================================================
// cylonWithBrightnessControl() : This is the 2nd LED effect. The cylon colour is red (hue=0), and the brightness is controlled by the potentiometer
//===================================================================================================================================================
void cylonWithBrightnessControl(){
      constSpeed = true; // Make speed constant
      showLED(LEDPosition, 0, 255, potVal);               // Brightness is controlled by potentiometer.
      fadeLEDs(16);                                       // Fade LEDs by a value of 16
      setDelay(LEDSpeed);                                 // The LEDSpeed is constant, so the delay is constant
}


//===================================================================================================================================================
// cometEffect() :  This is the 3rd LED effect. The random brightness of the trailing LEDs produces an interesting comet-like effect.
//===================================================================================================================================================
void cometEffect(){
      constSpeed = false; // The speed will be controlled by the slope of the accelerometer (y-Axis)
      showLED(LEDPosition, potVal, 255, intensity);        // Hue will change with potentiometer.
      
      //The following lines create the comet effect
      bright = random(50, 100); // Randomly select a brightness between 50 and 100
      leds[LEDPosition] = CHSV((potVal+40),255, bright); // The trailing LEDs will have a different hue to the leading LED, and will have a random brightness
      fadeLEDs(8);                                         // This will affect the length of the Trailing LEDs
      setDelay(LEDSpeed);                                  // The LEDSpeed will be affected by the slope of the Accelerometer's y-Axis
}


//===================================================================================================================================================
// fireStarter() : This is the 4th LED effect. It starts off looking like a ball of fire, leaving a trail of little fires. But as you
//                 turn the potentiometer, it becomes more like a shooting star with a rainbow-sparkle trail.
//===================================================================================================================================================
void fireStarter(){
      constSpeed = false; // The speed will be controlled by the slope of the accelerometer (y-Axis)
      ledh[LEDPosition] = potVal;                          // Hue is controlled by potentiometer
      showLED(LEDPosition, ledh[LEDPosition], 255, intensity); 
      
      //The following lines create the fire starter effect
      bright = random(50, 100); // Randomly select a brightness between 50 and 100
      ledb[LEDPosition] = bright;                          // Assign this random brightness value to the trailing LEDs
      sparkle(potVal/5);                                   // Call the sparkle routine to create that sparkling effect. The potentiometer controls the difference in hue from LED to LED.
      fadeLEDs(1);                                         // A low number creates a longer tail
      setDelay(LEDSpeed);                                  // The LEDSpeed will be affected by the slope of the Accelerometer's y-Axis
}


//===================================================================================================================================================
// levelSense() : This is the 5th and final LED effect. The accelerometer is used in conjunction with the LED strip to create a digital "Spirit" Level.
//                You can use the illuminated LEDs to identify the angle of the LED strip
//===================================================================================================================================================
void levelSense(){
      constSpeed = true;
      LEDPosition = constrain(map(analogRead(yPin), 230, 640, 1, NUM_LEDS-1), 0 , NUM_LEDS-1);
      
      //Jitter correction: this will reduce the amount of jitter caused by the accelerometer reading variability
      if(abs(LEDPosition-oldPos) < 2){
        LEDPosition = oldPos;
      }
      
      //The following lines of code will ensure the colours remain within the red to green range, with green in the middle and red at the ends.
      hue = map(LEDPosition, 0, NUM_LEDS-1, 0, 200);
      if (hue>100){
         hue = 200 - hue;
      }
      
      //Illuminate 2 LEDs next to each other
      showLED(LEDPosition, hue, 255, intensity); 
      showLED(LEDPosition-1, hue, 255, intensity);              
      
      //If the position moves, then fade the old LED positions by a factor of 25 (high numbers mean shorter tail)
      fadeLEDs(25);                               
      oldPos = LEDPosition; 
}


//===================================================================================================================================================
// fadeLEDs(): This function is used to fade the LEDs back to black (OFF) 
//===================================================================================================================================================
void fadeLEDs(int fadeVal){
  for (int i = 0; i<NUM_LEDS; i++){
    leds[i].fadeToBlackBy( fadeVal );
  }
}



//===================================================================================================================================================
// showLED() : is used to illuminate the LEDs 
//===================================================================================================================================================
void showLED(int pos, byte LEDhue, byte LEDsat, byte LEDbright){
  leds[pos] = CHSV(LEDhue,LEDsat,LEDbright);
  FastLED.show();
}


//===================================================================================================================================================
// setDelay() : is where the speed of the LED animation sequence is controlled. The speed of the animation is controlled by the LEDSpeed variable.
//              and cannot go faster than the maxLEDSpeed variable.
//===================================================================================================================================================
void setDelay(int LSpeed){
  animationDelay = maxLEDSpeed - abs(LSpeed);
  delay(animationDelay);
}


//===================================================================================================================================================
// sparkle() : is used by the fireStarter routine to create a sparkling/fire-like effect
//             Each LED hue and brightness is monitored and modified using arrays  (ledh[]  and ledb[])
//===================================================================================================================================================
void sparkle(byte hDiff){
  for(int i = 0; i < NUM_LEDS; i++) {
    ledh[i] = ledh[i] + hDiff;                // hDiff controls the extent to which the hue changes along the trailing LEDs
    
    // This will prevent "negative" brightness.
    if(ledb[i]<3){
      ledb[i]=0;
    }
    
    // The probability of "re-igniting" an LED will decrease as you move along the tail
    // Once the brightness reaches zero, it cannot be re-ignited unless the leading LED passes over it again.
    if(ledb[i]>0){
      ledb[i]=ledb[i]-2;
      sparkTest = random(0,bright);
      if(sparkTest>(bright-(ledb[i]/1.1))){
        ledb[i] = bright;
      } else {
        ledb[i] = ledb[i] / 2;                  
      }
    }
    leds[i] = CHSV(ledh[i],255,ledb[i]);
  }
}


 

NeoPixel Strip connection

The NeoPixel strip is rolled up when you first get it. You will notice that there are wires on both sides of the strip. This allows you to chain LED strips together to make longer strips. The more LEDs you have, the more current you will need. Connect your Arduino and power supply to the left side of the strip, with the arrows pointing to the right side of the strip.
 

Follow the Arrows

The arrows are quite hard to see on this particular LED strip because they are so small, plus they are located right under the thicker part of the NeoPixel weatherproof sheath. I have circled the arrows in RED so that you know where to look:

 


NeoPixel Strip Wires

There are 4 wires coming from either side of the NeoPixel LED strip:
 
  One red wire, one white wire, and two black wires.
 
It doesn't matter which Black wire you use to connect to the power supply (or Arduino) GND. Both black wires appear to be going to the same pin on the LED strip anyway. Use the table below to make the necessary NeoPixel Strip connections to the Arduino and power supply.


Large Capacitor

Adafruit also recommend the use of a large capacitor across the + and - terminals of the LED strip to "prevent the initial onrush of current from damaging the pixels". Adafruit recommends a capacitor that is 1000uF, 6.3V or higher. I used a 4700uF 16V Electrolytic Capacitor.

Resistor on Data Pin

Another recommendation from Adafruit is to place a "300 to 500 Ohm resistor" between the Arduino's data pin and the data input on the first NeoPixel to prevent voltage spikes that can damage the first pixel. I used a 330 Ohm resistor.
 

Powering your Arduino (USB vs Power supply)

You can power your Arduino board via USB cable or via the LED strip power supply.
*** Please note: different power supplies will yield different accelerometer readings. I noticed this when changing the Arduino's power source from USB to LED power supply. My final sketch was designed to eliminate the USB/computer connection, hence I have chosen to power the Arduino via the power supply. The fritzing sketch below shows the Arduino being powered by a power supply only.

**WARNING: If you decide to power your Arduino UNO via a USB cable, please make sure to remove (or disconnect) the wire that goes to the the Arduino VIN pin. The GND connections remain unchanged.


Fritzing Sketch - NeoPixel strip connection


 

Potentiometer connection

The potentiometer will be used to switch between the different LED sequences. When it reads zero, it will switch to the next sequence in the list. It will jump right back to the beginning after the last sequence. The potentiometer is also used to interact with the LEDs (e.g. controlling hue, brightness etc etc).
See the fritzing sketch below to add the potentiometer to this project.



 

Accelerometer connection (Y-axis)

The accelerometer makes the LEDs much more fun and interactive. We will only be using the Y-axis of the accelerometer in this sketch. By tilting the accelerometer from one side to the other, the LEDs react and respond accordingly. The accelerometer is an essential component of the digital spirit level sequence. That's right ! You can use this sketch to create your own spirit level. This digital version can also be used to measure angles !
 
Have a look below to see how to hook up the accelerometer to the Arduino. The Y-axis is connected to the Arduino analog pin 4. If you wanted to use the X and Z axis, connect them to one of the other available analog pins (eg. A3 and A5).




 

Let the fun begin !!

Now that you have the Arduino code uploaded to the Arduino, and have made all of the necessary wire/component connections, it is time to turn on the power supply.
 

Sequence 1: Cylon with Hue control

The LEDs will move from one end of the strip to the other. It should start off as a RED cylon effect. As you turn the potentiometer clockwise, the colour of the LEDs will change and move through the various colours of the rainbow. If the potentiometer reading gets back to zero (fully anti-clockwise), it will move to sequence 2.
 

Sequence 2: Cylon with brightness control

You will see that the LEDs have turned off. The potentiometer readings correlate with the LED brightness. At the start of this sequence, the potentiometer readings will be zero, therefore the brightness will be zero (LEDs turned off). As you turn the potentiometer clockwise, the readings increase, and so will the brightness of the LEDs.
 

Sequence 3: Comet effect with Hue and direction control

This is where the real fun begins. You control the hue of the leading LED with the potentiometer, however the LED will move along the LED strip as though it were affected by gravity. As it hits the end of the LED strip, it will bounce for a while and eventually come to a stop. The more you tilt the accelerometer, the greater the acceleration of the leading LED. The trailing LEDs have an interesting randomised glow, which creates the "comet" effect.
 

Sequence 4: FireStarter / Rainbow effect : Hue and direction control

The initial colours of LEDs in this sequence creates a fire-like animation. As the leading LED moves along the LED strip, it appears to ignite the LEDs in its path, leaving a fire trail behind it. The fire effect is best when you turn the potentiometer clockwise slightly to introduce a small amount of yellow into the mix of colours. As you turn the potentiometer further clockwise, the fire trail turns into a pretty rainbow trail. The accelerometer affects the leading LED in the same way as the previous sequence.
 

Sequence 5: Digital spirit level

This sequence was my original idea for this project, however I thought it would be nice to share some of the other cool effects I created on my journey of discovery. The idea was to make a digital version of a spirit level. I originally wanted the LEDs to represent a spirit level bubble that would "float" according to the vertical/horizontal position of the LED strip. However, as I played around with this sketch, I discovered that it could potentially be used to measure the angle of the strip relative to the horizon. The angle can be determined by the illuminated LED. If the strip is horizontal, the illuminated LEDs will be close to the middle of the strip, and their colour will be green. If the strip is vertical, the illuminated LEDs will be close to end of the strip, and their colour will be red. The colour is just an additional visual indicator.
 


Concluding Comments

The NeoPixel Digital RGB LED strip is a lot of fun. The FastLED library makes for easy programming, and allows you to get up and running really quickly. 144 LEDs on a single strip means you have plenty of room for creative algorithms and lighting effects. Add a few sensors, and "pretty" quickly turns into "awesome" !!
 
This tutorial shows you how to control a "144 NeoPixel per metre Digital RGB LED strip" with an Arduino UNO. Feel free to share your own LED creations in the comments below.



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Tutorial – LM3915 Logarithmic Dot/Bar Display Driver IC

Introduction

This is the second of three articles that will examine the LM391x series of LED driver ICs. The first covered the LM3914, this will cover the LM3915 and the LM3916 will follow. The goal of these is to have you using the parts in a small amount of time and experiment with your driver ICs, from which point you can research further into their theory and application.

Although these parts have been around for many years, the LM3915 isn’t used that much however for the sake of completeness we’re writing the tutorial. The LM3915 offers a simple way to display a logarithmic voltage level using one or more groups of ten LEDs with a minimum of fuss. If you’re wanting to make a VU meter, you should use the LM3916 which we will cover in the final instalment of this trilogy.

Instead of having each LED represent a voltage level as with the LM3914, each LED connected to the LM3915 represents a 3 dB (decibel) change in the power level of the signal. For more on decibels, check out Wikipedia.

To display these power level changes we’ll run through a couple of examples that you can use in your own projects and hopefully give you some ideas for the future. Originally by National Semiconductor, the LM391X series is now handled by Texas Instruments.

Getting Started

You will need the LM3915 data sheet, so please download that and keep it as a reference. First – back to basics. The LM3915 controls ten LEDs. It controls the current through the LEDs with the use of only one resistor, and the LEDs can appear in a bar graph or single ‘dot’ when in use. The LM3915 contains a ten-stage voltage divider, each stage when reached will illuminate the matching LED (and those below it in level meter mode).

Let’s consider the most basic of examples (from page two of the data sheet) – a simple logarithmic display of voltage between 0 and 10V:

After building the circuit you can connect a signal to measure via pin 5, and the GND to pin 2. We’ve built the circuit exactly as above on some stripboard for demonstration purposes, with the only difference being the use of an 8.2kΩ resistor for R2:

To show this in action we use a signal of varying AC voltage – a sine wave at around 2 kHz. In the following video, you can see the comparison of the signal’s voltage against the LEDs being illuminated, and you will see the logarithmic voltage increase represented by the LEDs:

We used the bar display mode for the voltage increase, and the dot display mode for the voltage decrease. Did you notice that during the voltage decrease, the LEDs below the maximum level being displayed were dim? As the signal’s voltage was varying very quickly, the change in the LED’s location is a blur due to the speed of change. In the video below, we’ve slowed the frequency right down but kept the same maximum voltage.

Well that was a lot of fun, and gives you an idea of what is possible with the LM3915.

Displaying weaker signals

In non-theoretical situations your input signal won’t conveniently be between 0 and 10 V. For example the line level on audio equipment can vary between 1 and 3V peak to peak. For example, here’s a random DSO image from measuring the headphone output on my computer whilst playing some typical music:

Although it’s an AC signal we’ll treat it as DC for simplicity. So to display this random low DC voltage signal we’ll reduce the range of the display to 0~3V DC. This is done using  the same method as with the LM3914 – with maths and different resistors.

Consider the following formulae:

As you can see the LED current (Iled) is simple, however we’ll need to solve for R1 and R2 with the first formula to get our required Vref of 3V. For our example circuit I use 2.2kΩ for R2 which gives a value of 1.8kΩ for R1. However putting those values in the ILED formula gives a pretty low current for the LEDs, about 8.3 mA. Live and learn – so spend time experimenting with values so you can match the required Vref and ILED.

Nevertheless in this video below we have the Vref of 3V and some music in from the computer as a sample source of low-voltage DC. This is not a VU meter! Wait for the LM3916 article to do that.

Again due to the rapid rate of change of the voltage, there is the blue between the maximum level at the time and 0V.

Chaining multiple LM3915s

This is covered well in the data sheet, so read it for more on using two LM3915s. Plus there are some great example circuits in the data sheet, for example the 100W audio power meter on page 26 and the vibration meter (using a piezo) on page 18.

Conclusion

As always I hope you found this useful. Don’t forget to stay tuned for the final instalment about the LM3916. And if you made it this far – check out my new book “Arduino Workshop” from No Starch Press.

In the meanwhile have fun and keep checking into tronixstuff.com. Why not follow things on twitterGoogle+, subscribe  for email updates or RSS using the links on the right-hand column? And join our friendly Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.

The post Tutorial – LM3915 Logarithmic Dot/Bar Display Driver IC appeared first on tronixstuff.

Tronixstuff 09 Dec 04:05
bar  display  dot  driver  electronics  example  ic  level  lm3914  lm3915  lm3916  logarithmic  ti  tronixstuff  tutorial  voltmeter  vu  

Tutorial – LM3915 Logarithmic Dot/Bar Display Driver IC

Introduction

This is the second of three articles that will examine the LM391x series of LED driver ICs. The first covered the LM3914, this will cover the LM3915 and the LM3916 will follow. The goal of these is to have you using the parts in a small amount of time and experiment with your driver ICs, from which point you can research further into their theory and application.

Although these parts have been around for many years, the LM3915 isn’t used that much however for the sake of completeness we’re writing the tutorial. The LM3915 offers a simple way to display a logarithmic voltage level using one or more groups of ten LEDs with a minimum of fuss. If you’re wanting to make a VU meter, you should use the LM3916 which we will cover in the final instalment of this trilogy.

Instead of having each LED represent a voltage level as with the LM3914, each LED connected to the LM3915 represents a 3 dB (decibel) change in the power level of the signal. For more on decibels, check out Wikipedia.

To display these power level changes we’ll run through a couple of examples that you can use in your own projects and hopefully give you some ideas for the future. Originally by National Semiconductor, the LM391X series is now handled by Texas Instruments.

Getting Started

You will need the LM3915 data sheet, so please download that and keep it as a reference. First – back to basics. The LM3915 controls ten LEDs. It controls the current through the LEDs with the use of only one resistor, and the LEDs can appear in a bar graph or single ‘dot’ when in use. The LM3915 contains a ten-stage voltage divider, each stage when reached will illuminate the matching LED (and those below it in level meter mode).

Let’s consider the most basic of examples (from page two of the data sheet) – a simple logarithmic display of voltage between 0 and 10V:

After building the circuit you can connect a signal to measure via pin 5, and the GND to pin 2. We’ve built the circuit exactly as above on some stripboard for demonstration purposes, with the only difference being the use of an 8.2kΩ resistor for R2:

To show this in action we use a signal of varying AC voltage – a sine wave at around 2 kHz. In the following video, you can see the comparison of the signal’s voltage against the LEDs being illuminated, and you will see the logarithmic voltage increase represented by the LEDs:

We used the bar display mode for the voltage increase, and the dot display mode for the voltage decrease. Did you notice that during the voltage decrease, the LEDs below the maximum level being displayed were dim? As the signal’s voltage was varying very quickly, the change in the LED’s location is a blur due to the speed of change. In the video below, we’ve slowed the frequency right down but kept the same maximum voltage.

Well that was a lot of fun, and gives you an idea of what is possible with the LM3915.

Displaying weaker signals

In non-theoretical situations your input signal won’t conveniently be between 0 and 10 V. For example the line level on audio equipment can vary between 1 and 3V peak to peak. For example, here’s a random DSO image from measuring the headphone output on my computer whilst playing some typical music:

Although it’s an AC signal we’ll treat it as DC for simplicity. So to display this random low DC voltage signal we’ll reduce the range of the display to 0~3V DC. This is done using  the same method as with the LM3914 – with maths and different resistors.

Consider the following formulae:

As you can see the LED current (Iled) is simple, however we’ll need to solve for R1 and R2 with the first formula to get our required Vref of 3V. For our example circuit I use 2.2kΩ for R2 which gives a value of 1.8kΩ for R1. However putting those values in the ILED formula gives a pretty low current for the LEDs, about 8.3 mA. Live and learn – so spend time experimenting with values so you can match the required Vref and ILED.

Nevertheless in this video below we have the Vref of 3V and some music in from the computer as a sample source of low-voltage DC. This is not a VU meter! Wait for the LM3916 article to do that.

Again due to the rapid rate of change of the voltage, there is the blue between the maximum level at the time and 0V.

Chaining multiple LM3915s

This is covered well in the data sheet, so read it for more on using two LM3915s. Plus there are some great example circuits in the data sheet, for example the 100W audio power meter on page 26 and the vibration meter (using a piezo) on page 18.

Conclusion

As always I hope you found this useful. Don’t forget to stay tuned for the final instalment about the LM3916. And if you made it this far – check out my new book “Arduino Workshop” from No Starch Press.

In the meanwhile have fun and keep checking into tronixstuff.com. Why not follow things on twitterGoogle+, subscribe  for email updates or RSS using the links on the right-hand column? And join our friendly Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.

Tronixstuff 09 Dec 04:05
bar  display  dot  driver  electronics  example  ic  level  lm3914  lm3915  lm3916  logarithmic  ti  tronixstuff  tutorial  voltmeter  vu  

Tutorial – LM3914 Dot/Bar Display Driver IC

Introduction

This is the first of three tutorials that will examine the LM391x series of LED driver ICs. In this first tutorial we cover the LM3914, then the LM3915 and LM3916 will follow. The goal of these tutorials is to have you using the parts in a small amount of time and experiment with your driver ICs, from which point you can research further into their theory and application.

Although these parts have been around for many years, the LM3914 in particular is still quite popular. It offers a simple way to display a linear voltage level using one or more groups of ten LEDs with a minimum of fuss.

With a variety of external parts or circuitry these LEDs can then represent all sorts of data, or just blink for your amusement. We’ll run through a few example circuits that you can use in your own projects and hopefully give you some ideas for the future. Originally by National Semiconductor, the LM391X series is now handled by Texas Instruments.

Getting Started

You will need the LM3914 data sheet, so please download that and keep it as a reference. So – back to basics. The LM3914 controls ten LEDs. It controls the current through the LEDs with the use of only one resistor, and the LEDs can appear in a bar graph or single ‘dot’ when in use. The LM3914 contains a ten-stage voltage divider, each stage when reached will illuminate the matching LED (and those below it in level meter mode).

Let’s consider the most basic of examples (from page two of the data sheet) – a voltmeter with a range of 0~5V:

 

The Vled rail is also connected to the supply voltage in our example. Pin 9 controls the bar/dot display mode – with it connected to pin 3 the LEDs will operate in bar graph mode, leave it open for dot mode. The 2.2uF capacitor is required only when “leads to the LED supply are 6″ or longer”. We’ve hooked up the circuit above, and created a 0~5V DC source via a 10kΩ potentiometer with a multimeter to show the voltage – in the following video you can see the results of this circuit in action, in both dot and bar graph mode:

Customising the upper range and LED current

Well that was exciting, however what if you want a different reference voltage? That is you want your display to have a range of 0~3 V DC? And how do you control the current flow through each LED? With maths and resistors. Consider the following formulae:

As you can see the LED current (Iled) is simple, our example is 12.5/1210 which returned 10.3 mA – and in real life 12.7 mA (resistor tolerance is going to affect the value of the calculations).

Now to calculate a new Ref Out voltage – for example  we’ll shoot for a 3 V meter, and keep the same current for the LEDs. This requires solving for R2 in the equation above, which results with R2 = -R1 + 0.8R1V. Substituting the values – R2 = -1210 + 0.8 x 1210 x 3 gives a value of 1694Ω for R2. Not everyone will have the E48 resistor range, so try and get something as close as possible. We found a 1.8 kΩ for R2 and show the results in the following video:

You can of course have larger display range values, but a supply voltage of no more than 25 V will need to be equal to or greater than that value. E.g. if you want a 0~10 V display, the supply voltage must be >= 10V DC.

Creating custom ranges

Now we’ll look at how to create  a lower range limit, so you can have displays that (for example) can range from a non-zero positive value. For example, you want to display levels between 3 and 5V DC. From the previous section, you know how to set the upper limit, and setting the lower limit is simple – just apply the lower voltage to pin 4 (Rlo).

You can derive this using a resistor divider or other form of supply with a common GND. When creating such circuits, remember that the tolerance of the resistors used in the voltage dividers will have an affect on the accuracy. Some may wish to fit trimpots, which after alignment can be set permanently with a blob of glue.

Finally, for more reading on this topic – download and review the TI application note.

Chaining multiple LM3914s

Two or more LM3914s can be chained together to increase the number of LEDs used to display the levels over an expanded range. The circuitry is similar to using two independent units, except the REFout (pin 7) from the first LM3914 is fed to the REFlo (pin 4) of the second LM3914 – whose REFout is set as required for the upper range limit. Consider the following example schematic which gave a real-world range of 0~3.8V DC:

The 20~22kΩ resistor is required if you’re using dot mode (see “Dot mode carry” in page ten of the data sheet). Moving on, the circuit above results with the following:

Where to from here?

Now you can visually represent all sorts of low voltages for many purposes. There’s more example circuits and notes in the LM3914 data sheet, so have a read through and delve deeper into the operation of the LM3914. Furthermore Dave Jones from eevblog.com has made a great video whcih describes a practical application of the LM3914:

Conclusion

As always I hope you found this useful. Don’t forget to stay tuned for the second and third instalments using the LM3915 and LM3916. Full-sized images are on flickr. And if you made it this far – check out my new book “Arduino Workshop” from No Starch Press.

In the meanwhile have fun and keep checking into tronixstuff.com. Why not follow things on twitterGoogle+, subscribe  for email updates or RSS using the links on the right-hand column? And join our friendly Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.

The post Tutorial – LM3914 Dot/Bar Display Driver IC appeared first on tronixstuff.

Tronixstuff 13 Sep 15:13
bar  display  dot  driver  electronics  example  ic  led  level  lm3914  lm3915  lm3916  ti  tronixstuff  tutorial  voltmeter