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Multiple neopixels power supplies
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Multiple neopixels power supplies

by flounder on Fri Aug 11, 2017 2:48 am

I am involved in a project to have LEDs synchronize to music. It could involve up to ten meters of 30-unit neopixel strips. Back-of-the-envelope calculations indicate that at 60ma/RGB, one such strip would be 1.8A peak, and 10 meters would be 18A. I see at least two major problems: (a) getting a 20A 5V supply seems either unlikely or expensive and (b) the power drop across 10M will either result in very dim lights at the end, and/or vaporizing the copper of the first couple meters of strip as it tries to cope with delivering 18A.

To provide enough memory to support 300 neopixels, and for additional horsepower, I have chosen the Feather M0 Basic Proto.

I see a couple possible solutions:

(1) Use multiple 5A supplies, one every 2M. This means that the first two strips have DO1->DI2, +V1->+V2 and GND1->GND2. But the third strip has only DO2->DI3 and GND2->GND3, but +V2 is unconnected. A new power supply is connected to +V3 (with the 1000uF capacitor to ground) and its GND connected to the GND3 pin.

Potential problems include ground loops and the degradation of the control signal timing cause by capacitive and inductive loads across all the strips.

(2) Have one output pin drive no more than two strips; the next two strips are driven by another output pin. Each pair of strips has its own 5A power supply (all GND lines common), 1000uF capacitor, and 470ohm signal line resistor.

Potential problems include ground loops and degradation of the signal between the Feather and the data pin 2, 4, 6 or 8M away. Would a small coax be a better choice than 26ga wire? Twisted pair? Recommendations?

The goal is to select a color<->pitch map from violet to red, conpress it to the range using a logarithmic mapping (90Hz to 9KHz is the interesting range). Input will be MIDI, and there will be an "envelope" that defines "attack" and "decay" rates so the lights modulate "gently" with the music (for reasons too complex to explain here, we are guaranteed monophonic music; only one note at a time is played). The MIDI "volume" describes the "sustain" intensity, and attack/decay are linear slopes. So lots of memory and computing horsepower required, hence the M0 selection.

Any suggestions for how to control and power 10M of neopixels greatly appreciated.
Joe

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Re: Multiple neopixels power supplies

by adafruit_support_bill on Fri Aug 11, 2017 6:06 am

There is no problem powering strips from multiple power supplies. You can have a your entire 10 meter strip controlled by a single pin, but powered by multiple supplies.

Simply divide the strip into separately powered sections. Cut the 5v connections between sections, but keep the signal and ground connections between them.

https://learn.adafruit.com/adafruit-neo ... -practices

Another issue I see is that you are using a Feather M0 which is a 3.3v processor. You will need to use a 3.3v-5v level shifter for the signal. We recommend the 74AHCT125.

https://www.adafruit.com/product/1787

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Please be positive and constructive with your questions and comments.