ws2801 pixels with a purposely unreliable power source

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dvdv
 
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ws2801 pixels with a purposely unreliable power source

Post by dvdv »

I've done a number of projects using ws2801 led pixels, and I've done a number of projects using a hand powered generator for intermittent fun, but this time I tried to do both at once.

A McMasterCarr gearmotor driven by a hand wheel provides 0-24v. A Velleman kit voltage regulator keeps that at a steady 4.86v. This runs a metro mini powered to the usb pin, and parallel, about 7 pixels. It mostly works. Gently turning the wheel makes everything work as expected. Turning a little faster causes the first pixel to flicker blue or white, all the other pixels work perfectly. I even altered the program to not use the first pixel, writing it off in setup().

If I wasn't worried that the chip would burn out, I could just leave the first pixel hidden in the enclosure.

I am thinking of adding a second voltage regulator. First regulate the variable voltage from the hand wheel generator to around 9v, run the metro mini from the Vin pin, then regulate to 5v (preserving common ground) and run the pixels from that. That way the data signal would be from the metro mini's voltage regulator.

If anyone has any pointers for this strange set up or even clues as to what is happening I would love to hear.

Also, as the system powers down and voltage drops, sometimes the leds brown out (turn red) before going off. This is momentary and not a deal breaker, but I would love a way to instruct the leds to turn off before brown out if the primary voltage drops. (The regulator's capacitor is huge, and there is probably enough processing time to do this before it discharges) I can't just read that voltage from an analog pin, do I just need a resistor to drop that voltage into the readable range?

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adafruit_support_bill
 
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Re: ws2801 pixels with a purposely unreliable power source

Post by adafruit_support_bill »

Brushed motors tend to generate a lot of EMI in operation as either a motor or a generator. If that noise gets picked up on the signal wires to the pixels it could explain the misbehavior. You can try to minimize that at the source with some .01uF ceramic caps. Solder one between the motor terminals, and one from each terminal to the metal motor case as in the photo below.

Also, you should be able to divide down the raw voltage from the generator to keep it within the range of your analog pin for monitoring.

Image

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dvdv
 
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Re: ws2801 pixels with a purposely unreliable power source

Post by dvdv »

Thanks, I had googled my way to a voltage divider. I really appreciate the pointer on the emi.

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