Posts with «analog» label

Hack an Old DC Motor to Provide Rotary Input

Watch a Redditor share how he hacked a DC motor and hooked it up to an Arduino to use as an encoder.

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The post Hack an Old DC Motor to Provide Rotary Input appeared first on Make: DIY Projects, How-Tos, Electronics, Crafts and Ideas for Makers.

Printing Text with a Chart Recorder

Chart recorders are vintage devices that were used to plot analog values on paper. They’re similar to old seismometers which plot seismic waves from earthquakes. The device has a heated pen which moves across a piece of thermally sensitive paper. This paper is fed through the machine at a specified rate, which gives two dimensions of plotting.

[Marv] ended up getting a couple of discontinued chart recorders and figured out the interface. Five parallel signals control the feed rate of the paper, and an analog voltage controls the pen location. The next logical step was to hook up an Arduino to control the plotter.

However, once the device could plot analog values, [Marv] quickly looked for a new challenge. He wanted to write characters and bitmaps using the device, but this would require non-continuous lines. By adding a solenoid to lift the pen, he built a chart recorder printer.

After the break, check out a video of the chart recorder doing something it was never intended to do. If you happen to have one of these chart recorders, [Marv] included all of the code in his writeup to help you build your own.


Filed under: classic hacks

Arduino Tutorials – Chapter 22 – the AREF pin

Learn how to measure smaller voltages with greater accuracy using your Arduino.

This is chapter twenty-two of our huge Arduino tutorial seriesUpdated 12/12/2013

In this chapter we’ll look at how you can measure smaller voltages with greater accuracy using the analogue input pins on your Arduino or compatible board in conjunction with the AREF pin. However first we’ll do some revision to get you up to speed. Please read this post entirely before working with AREF the first time.

Revision

You may recall from the first few chapters in our tutorial series that we used the analogRead() function to measure the voltage of an electrical current from sensors and so on using one of the analogue input pins. The value returned from analogRead() would be between zero an 1023, with zero representing zero volts and 1023 representing the operating voltage of the Arduino board in use.

And when we say the operating voltage – this is the voltage available to the Arduino after the power supply circuitry. For example, if you have a typical Arduino Uno board and run it from the USB socket – sure, there is 5V available to the board from the USB socket on your computer or hub – but the voltage is reduced slightly as the current winds around the circuit to the microcontroller – or the USB source just isn’t up to scratch.

This can easily be demonstrated by connecting an Arduino Uno to USB and putting a multimeter set to measure voltage across the 5V and GND pins. Some boards will return as low as 4.8 V, some higher but still below 5V. So if you’re gunning for accuracy, power your board from an external power supply via the DC socket or Vin pin – such as 9V DC. Then after that goes through the power regulator circuit you’ll have a nice 5V, for example:

This is important as the accuracy of any analogRead() values will be affected by not having a true 5 V. If you don’t have any option, you can use some maths in your sketch to compensate for the drop in voltage. For example, if your voltage is 4.8V – the analogRead() range of 0~1023 will relate to 0~4.8V and not 0~5V. This may sound trivial, however if you’re using a sensor that returns a value as a voltage (e.g. the TMP36 temperature sensor) – the calculated value will be wrong. So in the interests of accuracy, use an external power supply.

Why does analogRead() return a value between 0 and 1023?

This is due to the resolution of the ADC. The resolution (for this article) is the degree to which something can be represented numerically. The higher the resolution, the greater accuracy with which something can be represented. We measure resolution in the terms of the number of bits of resolution.

For example, a 1-bit resolution would only allow two (two to the power of one) values – zero and one. A 2-bit resolution would allow four (two to the power of two) values – zero, one, two and three. If we tried to measure  a five volt range with a two-bit resolution, and the measured voltage was four volts, our ADC would return a numerical value of 3 – as four volts falls between 3.75 and 5V. It is easier to imagine this with the following image:

 So with our example ADC with 2-bit resolution, it can only represent the voltage with four possible resulting values. If the input voltage falls between 0 and 1.25, the ADC returns numerical 0; if the voltage falls between 1.25 and 2.5, the ADC returns a numerical value of 1. And so on. With our Arduino’s ADC range of 0~1023 – we have 1024 possible values – or 2 to the power of 10. So our Arduinos have an ADC with a 10-bit resolution.

So what is AREF? 

To cut a long story short, when your Arduino takes an analogue reading, it compares the voltage measured at the analogue pin being used against what is known as the reference voltage. In normal analogRead use, the reference voltage is the operating voltage of the board. For the more popular Arduino boards such as the Uno, Mega, Duemilanove and Leonardo/Yún boards, the operating voltage of 5V. If you have an Arduino Due board, the operating voltage is 3.3V. If you have something else – check the Arduino product page or ask your board supplier.

So if you have a reference voltage of 5V, each unit returned by analogRead() is valued at 0.00488 V. (This is calculated by dividing 1024 into 5V). What if we want to measure voltages between 0 and 2, or 0 and 4.6? How would the ADC know what is 100% of our voltage range?

And therein lies the reason for the AREF pin. AREF means Analogue REFerence. It allows us to feed the Arduino a reference voltage from an external power supply. For example, if we want to measure voltages with a maximum range of 3.3V, we would feed a nice smooth 3.3V into the AREF pin – perhaps from a voltage regulator IC. Then the each step of the ADC would represent around 3.22 millivolts (divide 1024 into 3.3).

Note that the lowest reference voltage you can have is 1.1V. There are two forms of AREF – internal and external, so let’s check them out.

External AREF

An external AREF is where you supply an external reference voltage to the Arduino board. This can come from a regulated power supply, or if you need 3.3V you can get it from the Arduino’s 3.3V pin. If you are using an external power supply, be sure to connect the GND to the Arduino’s GND pin. Or if you’re using the Arduno’s 3.3V source – just run a jumper from the 3.3V pin to the AREF pin.

To activate the external AREF, use the following in void setup():

analogReference(EXTERNAL); // use AREF for reference voltage

This sets the reference voltage to whatever you have connected to the AREF pin – which of course will have a voltage between 1.1V and the board’s operation voltage.

Very important note – when using an external voltage reference, you must set the analogue reference to EXTERNAL before using analogRead(). This will prevent you from shorting the active internal reference voltage and the AREF pin, which can damage the microcontroller on the board.

If necessary for your application, you can revert back to the board’s operating voltage for AREF (that is – back to normal) with the following:

analogReference(DEFAULT);

Now to demonstrate external AREF at work. Using a 3.3V AREF, the following sketch measures the voltage from A0 and displays the percentage of total AREF and the calculated voltage:

#include <LiquidCrystal.h>
LiquidCrystal lcd(8,9,4,5,6,7);

int analoginput = 0; // our analog pin
int analogamount = 0; // stores incoming value
float percentage = 0; // used to store our percentage value
float voltage =0; // used to store voltage value

void setup()
{
  lcd.begin(16, 2);
  analogReference(EXTERNAL); // use AREF for reference voltage
}

void loop()
{
  lcd.clear();
  analogamount=analogRead(analoginput);
  percentage=(analogamount/1024.00)*100;
  voltage=analogamount*3.222; // in millivolts
  lcd.setCursor(0,0);
  lcd.print("% of AREF: ");
  lcd.print(percentage,2);
  lcd.setCursor(0,1);  
  lcd.print("A0 (mV): ");
  lcd.println(voltage,2);
  delay(250);
}

The results of the sketch above are shown in the following video:

Internal AREF

The microcontrollers on our Arduino boards can also generate an internal reference voltage of 1.1V and we can use this for AREF work. Simply use the line:

analogReference(INTERNAL);

For Arduino Mega boards, use:

analogReference(INTERNAL1V1);

in void setup() and you’re off. If you have an Arduino Mega there is also a 2.56V reference voltage available which is activated with:

analogReference(INTERNAL2V56);

Finally – before settling on the results from your AREF pin, always calibrate the readings against a known good multimeter.

Conclusion

The AREF function gives you more flexibility with measuring analogue signals. If you are interested in using specific ADC components, we have tutorials on the ADS1110 16-bit ADC and the NXP PCF 8591 8-bit A/D and D/A IC.

Stay tuned for upcoming Arduino tutorials by subscribing to the blog, RSS feed (top-right), twitter or joining our Google Group. And if you enjoyed the tutorial, or want to introduce someone else to the interesting world of Arduino – check out my book (now in a third printing!) “Arduino Workshop” from No Starch Press.

 

The post Arduino Tutorials – Chapter 22 – the AREF pin appeared first on tronixstuff.

Gertboard extender for Raspberry Pi ships to advanced tinkerers

If a seemingly infinitely programmable mini computer like the Raspberry Pi is just too... limiting, we've got good news: the Gertboard extender has started shipping. The $48 companion board reaching customers' doorsteps converts analog to digital and back for Raspberry Pi fans developing home automation, robotics and just about anything else that needs a translation between the computing world and less intelligent objects. The one catch, as you'd sometimes expect from a homebrew project, is the need for some assembly -- you'll have to solder together Gert van Loo's Arduino-controlled invention on your own. We imagine the DIY crowd won't mind, though, as long as they can find the fast-selling Gertboard in the first place.

[Image credit: Stuart Green, Flickr]

Filed under: Misc

Gertboard extender for Raspberry Pi ships to advanced tinkerers originally appeared on Engadget on Wed, 17 Oct 2012 03:58:00 EST. Please see our terms for use of feeds.

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Tweephone is a rotary phone Twitter client, even your grandma could love

The collectives behind the Tweephone, UP digital Bureau and Unteleported tech agency, claim that it's the first analog Twitter client. We find that hard to believe but, while we've seen rotary phone-based Twitter tools before and analog meters that measure microblogging activity, we couldn't come up with a single example of a client that lets you punch in messages through non-digital means. Even if it's not the first of its kind, the Tweephone is still a pretty neat hack. Inside the old-school chassis is the ubiquitous Arduino, which interprets your pulls of the dial as letters. Like a phone with only a dial pad, you'll have to ring up numbers multiple times to get the right letter (i.e. dial "2" three times to get a "c"). It definitely not the most efficient method for sending out 140-character missives, but certainly one of the more unique. Check out the video after the break to see it in action.

Continue reading Tweephone is a rotary phone Twitter client, even your grandma could love

Tweephone is a rotary phone Twitter client, even your grandma could love originally appeared on Engadget on Tue, 01 Nov 2011 19:04:00 EST. Please see our terms for use of feeds.

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