Posts with «stroboscope» label

Arduino Stroboscope Animation


This tutorial will show you how to build your own Stroboscopic Animator using Magzor's Mechanotronic Design Portal as a starting point. Magzor Corporation is a business in California that is trying really hard to simplify robotic design. They want to enable users with little to no engineering experience to design and manufacture a custom robot by themselves in a matter of hours.

What is a stroboscope? A stroboscope is an instrument that uses a strobe light to make a moving object look stationary… We will use this feature to create an interesting 4 picture animation on a rotating disk.

 


 
Have a look at the video below to see the project in action, and the MDP process walk-through:


 

Video



 
 

Parts Required:


 

Magzor Schematic Diagram

Click to zoom ...

 

Further build instructions can be obtained by selecting the components in the Mechanotronics Design Portal within the Magzor website. Generating the build, and then selecting "Setup Instructions" tab at the top of the page. See video above to see this process in action.
 
 

Arduino Sketch


Make sure to copy and paste the following code into your Arduino IDE. It doesn't seem to work directly from the browser. You also need to install the Arduino Magzor I2C library ( http://magzor.com/downloads/ )


 

Putting it together


 

Arduino MEGA


 

Magzor I2C board


 

MIC Boards


 

MIC Boards Assembled


 

Sensors, Modules and Shields - all put together


 

Motor with Bracket and Wire


 

Picture lined up with magnet on disk


 

Stroboscopic Animation


 

The Arduino MEGA microcontroller listens for the hall effect sensor to be triggered by the south facing side of the magnet on the underside of the rotating disk. As the magnet moves over the hall effect sensor, the sensor is triggered and the Arduino instructs the LED to blink for a fraction of a second. By manipulating the delay after the trigger time, we can get the LED to blink when one of the four images on the rotating disk is towards the front position. And if we get the timing right, we can make a simple animation.
 
If you watch the video above, you will see that the image bounces around a little bit. The duration of each frame is determined by the speed of the rotating disk (or motor), and the number of LED flashes per frame. Any changes in rotation speed will affect the position of the picture when the LED blinks. My rotating disk is not completely semetrical or centred correctly, and therefore a bit jumpy… but you get the idea. Bold images with high contrast seem to work best… Precision is key for this type of project. And if you can get the disk to rotate at a constant speed, you could probably do away with the hall effect sensors and magnets… however, in my case, these were essential in getting the project to work as intended.
 
This project is a lot of fun. You can really get creative by making your own pictures or 3 dimensional models (for a stop motion effect). Try different colours. It really is quite cool.


Concluding Comments


I would like to thank Magzor for supplying the components used in this tutorial, and letting me try out their MDP process. I really like the concept, the one stop shop which looks after you from beginning to end. Providing everything I needed to get the project off the ground. The point of this exercise was to go through the entire process of selecting the parts, build the project, and get it up and running. And I have done that in no time at all.
 
There is only one library to download and install, and the good thing is that you don't have to go hunting for it. The latest "correct" working version of the library is easy to find, right there on the Magzor website… Speaking of the Magzor website, please make sure to take a quick look around. It is quite impressive.



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LED strobe using dimmer board

In the evenings this week, I soldered up another PWM controller for the LED lamp projects, and programmed it with the ISP cable I made.  The intent was to use this dimmer either with the breakfast-room lighting fixture (which I’ve not made yet) or reprogram it to act as a strobe rather than a dimmer, to replace the Xenon-tube-based Velleman strobe kit that failed last Thanksgiving.

This project took me much longer than expected, because of stupid mistakes I made:

  • I forgot that there was a silkscreen error on the dimmer boards that I had designed.  The outline for the voltage regulator is flipped, because I had not noticed when reading the spec sheet shows the device from the bottom—I’m used to chip views being from the top.  This is the second time that I’ve soldered a voltage regulator on one of the boards backwards, and had to cut it off and replace it with a new one.  I guess I’d better take a permanent felt-tip marker and draw the correct orientation on the remaining boards, so that I don’t make that mistake a third time.
  • When playing with new code for the strobe, refamiliarizing myself with the ATtiny13A processor, I changed the prescaling on the system clock from the default 1.2MHz down to about 75kHz.  What I had not realized is that the on-chip clock is used during the reprogramming also, and the Arduino ISP is not set up for slowly clocked chips.  I found code for TinyISP, which has code for 128kHz clocks, but even when I modified it for 75kHz clocks I couldn’t reprogram the chip (always getting the “Yikes! invalid device signature” message with a signature of 0). Eventually, I gave up, unsoldered the ATtiny13A and put in a new one.  I’ll be very careful in future not to slow down the system clock so much.
  • I got the strobe working this morning, but when I looked at the output pin that was driving the FET gate, it was only going up to 1.3V, not 5V, and the pulse was much longer than I expected.  This mystified me for a while, but I finally realized that I had forgotten to turn the pin on as an output, so I was driving the output just through the built-in pullup resistor, resulting in a very large RC time constant.  The flat top I was seeing on the pulse was probably the Miller plateau.  Enabling the output pin correctly got me back to crisp 5V pulses of the designed duration.
  • The designed duration for the pulses was a bit too short, resulting in a somewhat dimmer than desired flash.  Lengthening the pulse to 1ms was fine for the slow strobes, but at high flash rates the strobe got too bright. So I reprogrammed the flashes so that the on-time was 1/64th of the off-time, but with a maximum on-time of 1.6ms. (I also tried on=off/128 with a maximum of 1ms, but I liked the 1/64 better).

I timed the strobe pulses from the board (looking at the output of the ATtiny13A pin 6, which is also connected to the MISO pin of the ISP header, so is easy to connect a jumper wire to) with PteroDAQ (through a voltage divider, to drop the voltage from 5V to 2.75V).  By triggering the PteroDAQ on edges of the signal, and averaging many measurements, I got very precise timing measurements:

setup on-time off-time
slowest setting, 1:64 1.63745ms 1.52372s
fastest setting, 1:64 104.958µs 6.98761ms
slowest setting, 1:128 955.277µs 1.55881s
fastest setting, 1:128 51.3123µs 6.99286ms

The difference in the “slowest” settings is probably just from my inability to set the knob identically—it has to be just above a threshold below which the strobe doesn’t flash at all. In any case, I have a period from 7.1ms (141Hz) to 1.525s (0.6556Hz), which is a pretty useful range.  I also made the range very smooth, by taking the 10-bit ADC range and converting it to this 215:1 range sort of exponentially with just a few instructions:

if adc<40, then OFF
exp = adc >> 7
frac = 0xff - (adc & 0x7f)
on_time = (frac << 8) >> exp

The tiny number of instructions provides a surprisingly smooth and strictly decreasing approximation to the desired exponential.

The transition is smooth because every time an increment increases the exponent, the frac part is doubled (from 0x80 to 0xff).I use a 16-bit word for the on_time and count it down with an interrupt once every 26.67µs (256 of the approximately 9.6MHz clock ticks). I think that I’ll do a similar thing for controlling the duty cycle of the dimmer, rather than the table of bytes that I currently use, though the duty cycle is limited to a single byte, so I’ll only have 256 levels, and not 1024, and I’ll want the duty cycle to increase exponentially, rather than decreasing, but those are easy fixes.

I also reduced the size of the program in flash, by getting rid of some of the overly general code from core13 and just manipulating the peripheral control registers directly.  I didn’t need to do this, as the ATtiny13A has 1kB of flash, but I got down to 364 bytes (and could probably strip out another 50–100 by getting rid of even more of core13).  The old dimmer code, which doesn’t have much more to do, currently takes 806 bytes, so I might try tightening that up tomorrow.

I also tried powering the strobe off a 9V battery.  The LED board takes about 117mA when turned on (see LED board I-vs-V curve), and if I keep the duty cycle below 1.5%, then the average current is dominated by the ATtiny13A’s worst-case 6mA current, and the total current for the board is probably less than 8mA.  According to Duracell’s data sheet for their 9V alkaline battery, I should be able to get about 50 hours of life before the voltage drops below 6.7V (at which point the LED board no longer maintains the constant current, but I could run the strobe a bit longer getting dimmer).  The 6.7V is also about the voltage where the LDO voltage regulator starts being unable to supply 5V to the ATtiny13A, though that is less of a bottleneck, as the chip can run with the 9.6MHz internal clock down to 3V with no problems.

The battery does not have to provide a full 117mA for the pulses, as there is a 470μF polymer electrolytic capacitor on the dimmer board.  Delivering 117mA for 1.6ms is only 187μC, so the voltage on the capacitor would dip at most 0.4V during the pulse, even without the battery.  The 9V battery has an internal resistance of 2Ω–4Ω, so it could provide 117mA with about a 0.35V drop, so the capacitor isn’t really necessary for one LED board.  It probably increases the efficiency slightly, as the I2R power loss in the internal resistor is reduced if the current is spread out (half the current for twice as long is only half the I2R loss).

I could put more LED boards on the strobe, as the dimmer is designed to handle 5A or more, but battery  operation would limit me to about 10 boards before the voltage drop was large enough to cause problems for the current regulation.  One LED board is bright enough for a Halloween pumpkin, but I could run wires between pumpkins to power several off the same controller.  (I could also keep the controller in the house, powered by a wall wart, and run wires out to the LED boards—I could then power 40 or 50 LED boards off the strobe, though I’d have to watch out for IR drop in the wiring.)

I might try wiring up 10 boards tomorrow, and see whether a battery really can power that many.


Filed under: Uncategorized Tagged: Arduino, Arduino as ISP, ATtiny, dimmable LED lamps, lamp, strobe, stroboscope

Do You Have Any Idea How Fast Your Blender Was Going?

Some people really love their smoothies. We mean really, really, love smoothies and everything about making them, especially the blenders. [Adam] is a big fan of blenders, and wanted to verify that his Vitamix blenders ran as fast as the manufacturer claimed. So he built not one, but two speed measuring setups. Scientific blender measurement method requires one to cross check their results to be sure, right?

Measuring the speed of a blender is all about the RPM. Appropriately, [Adam's] first measurement tool was an LED based stroboscope. Stroboscopes have been around for hundreds of years, and are a great way to measure how fast an object is rotating. Just adjust the speed of a flashing light until the rotating object appears frozen. The number of blinks per second is then equal to the Rotations Per Second (RPS) of the object being measured.Multiply by 60 seconds, and you’ve got RPM. [Adam] used an Arduino as the brains behind his stroboscope. He wired a dial up on his breadboard, and used it to adjust the flash rate of an LED. Since this was a quick hack, [Adam] skipped the display and just used the Arduino’s USB output to display speed measurements on his laptop.

There are possibilities for error with stroboscopes. [Adam] discovered that if the stroboscope was flashing at a multiple of the blade’s rotation speed, the blades would appear frozen, and he’d get an erroneous RPM value. Thankfully, [Adam's] Vitamix had asymmetric blades, which made the test a bit easier. He calculated his blades to be spinning at 380 RPS, or 23,000 RPM. Not satisfied with his results, [Adam] brought out Audacity, and ran a spectral analysis of the blender in operation. He found a peak at 378Hz, which was pretty darn close to his previous measurement. Since the blender has a 4 inch blade this all works out to a blade tip speed right around the claimed value of 270 MPH. We’re glad [Adam] found an answer to his blender questions, but our personal favorite blender hack still has to be the V8 blender created by the Top Gear crew.   [via HackerNews]


Filed under: Arduino Hacks, home hacks