Neopixel stuck on white after reading previous forum post

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mmachenry
 
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Neopixel stuck on white after reading previous forum post

Post by mmachenry »

Hi everyone,

I have a Neopixel array stuck on white. I've been reading the forums, especially this one where it's been recommended to insert a diode between the Trinket power and the source to reduce the pin voltage controlling the Neopixel. I've tried this but it doesn't seem to be working for me. Here's my setup.

My schematic is attached. I have DC/DC buck converter powered from a 12v car battery that is currently set to 4.8v to power the Trinket M0 (through a diode) and the Neopixel Stick 8 directly. There are four of them and they are in parallel and series as shown. Further more there is about a four foot triplet of wires running through a bus roof to get to them.

The trinket is powered at 3.7v which according to the Neopixel uber guide is a good way to go. If your pin voltage is too low, compared to input voltage of the Neopixels, it can be too quite. If it's the exact same voltage, apparently that's where you get a common stuck on white error. I have adhered to the guides recommendation to stick to powering the controlling source at around 70% of the Neopixel voltage. So since 3.7v + 1.1v (drop from a 1N4001) gives me 4.8v I power the pixels at that. 3.7v / 4.8v = 77% voltage.

However, my Neopixels are still after all that stuck on white. I am very confident that the program is running without error. A single Neopixel stick attached to the Trinket's 3V, GND and pin 2 gives me the behavior I'm looking for in the lights, a fading color changing pattern. But hooked up to the buck converter and powering separately from the Trinket, it's stuck on white.

Does anyone know what I might be able to do?
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Re: Neopixel stuck on white after reading previous forum pos

Post by adafruit_support_bill »

. . . it's been recommended to insert a diode between the Trinket power and the source to reduce the pin voltage controlling the Neopixel.
That is not what the diode is doing. It is reducing the voltage powering your Trinket. The control signal from the M0 remains fixed at 3.3v. And according to your schematic, the pixels themselves are still being powered by 5v.
If it's the exact same voltage, apparently that's where you get a common stuck on white error.
I have never seen or heard of that problem. We run Neopixels at 5v with 5v control signals all the time.
However, my Neopixels are still after all that stuck on white. I am very confident that the program is running without error.
If you post your code, we can take a look.

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mmachenry
 
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Re: Neopixel stuck on white after reading previous forum pos

Post by mmachenry »

That is not what the diode is doing. It is reducing the voltage powering your Trinket. The control signal from the M0 remains fixed at 3.3v. And according to your schematic, the pixels themselves are still being powered by 5v.
Oh, I think I must have misunderstood this from the forum link I posted. Folks were suggesting lowering the voltage to the Trinket's power.
I have never seen or heard of that problem. We run Neopixels at 5v with 5v control signals all the time.
Hm... interesting. I've done this before, and in fact done it in this test when I directly plug my single Neopixel stick into the 3v,GND,pin2 like I said originally. It was powering at 3v and the pin2 is the same. But with the buck converter it just doesn't work.

As for the code example, I've run this with many different pieces of code. The simplest one that turns the lights all white but shouldn't is this:

Code: Select all

import time
import board
import neopixel

pixel_pin = board.A1  
num_pixels = 16

pixels = neopixel.NeoPixel(pixel_pin, num_pixels, auto_write=False)

RED = (255, 0, 0)

while True:
    pixels.brightness = 1.0
    pixels.fill(RED)
    pixels.show()
    time.sleep(0.1)
Notice the one thing that might be odd here is that I have an array of size 16, and I have my pixels arranged in parallel and series. There are 8 per stick in a series. I'm not sure if you can get stuck on all white for all lights if you get this number wrong. I think that should probably be correct though.

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Re: Neopixel stuck on white after reading previous forum pos

Post by adafruit_support_bill »

Folks were suggesting lowering the voltage to the Trinket's power.
That is correct advice. But your diagram does not show that. You only lowered the supply voltage to the Trinket (which will not affect the control signal voltage). Your schematic still shows 5v to the pixels.

Since the M0 has a 3.3v output signal, you want to lower the supply voltage to the pixels. 3.7v for the pixel supply generally works well with a 3.3v control signal.
I've done this before, and in fact done it in this test when I directly plug my single Neopixel stick into the 3v,GND,pin2
The pixels are rated for 5v operation. We have found that they work reliably down to around 3.7v. 3.3v ( as you would get from the "3V" pin) is pretty low for reliable operation.
I have my pixels arranged in parallel and series.
Try with just a single stick attached. 2x Parallel operation generally works, but can get flaky if the voltages are marginal.

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Re: Neopixel stuck on white after reading previous forum pos

Post by mmachenry »

Thanks so much. So what I've taken from this is that I didn't understand that changing the input voltage would not affect the trinket out voltage. I misunderstood the forum post I read I think and that lead me to think that.

I have changed my circuit so that now there is no diode and the 5V input is changed to 3.7v. This has caused an odd behavior. Of the 16 lights that are in series (2 neo pixel sticks) I see one entire stick is white and the other is white, white, yellow, and the rest off. This is the same behavior for all sets of two that are parallel to each other.

Does this ring any bells? Am I hitting a common error? I'm wondering if I want a more reliable signal if I should have a transistor as the input to the lights input pin and trigger that transistor from the 3.3v trinket pin. Would that make this work better?

I will say it's going to be very difficult to wire this up in a way that's not in parallel so I'm pretty hopeful I can make a controlling circuit that allows this. Even if it means I need to have them all connected to their own separate transistors or something.

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Re: Neopixel stuck on white after reading previous forum pos

Post by adafruit_support_bill »

Please post some photos showing all of your soldering and connections.

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mmachenry
 
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Re: Neopixel stuck on white after reading previous forum pos

Post by mmachenry »

Here you go. There are two blue screw terminals on either side of the Trinket. The triple is connected to 3.3v, GND, and an analog pin on the Trinket. This is for a future potentiometer. The double is connected to power 3.3v and a digital pin on the Trinket for a future push button. Both are disconnected at the moment. They are soldered up but nothing is in the screw terminals. Also note that the Trinket is sitting inside two rows of female pin headers so it can be removed and put back in.
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Re: Neopixel stuck on white after reading previous forum pos

Post by adafruit_support_bill »

I don't see any connection for the Neopixels.

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mmachenry
 
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Re: Neopixel stuck on white after reading previous forum pos

Post by mmachenry »

I'm sorry, I wasn't clear on that. The neopixels are connected to the black three pin phono jack. 12v power comes in through the black 2.1mm barrel jack.

I've been wondering if possibly I would have less trouble if all the neo pixel lines were connected with their own transistor for the input pin that had 5v in and out but triggered by the 3.3v.

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Re: Neopixel stuck on white after reading previous forum pos

Post by adafruit_support_bill »

Neopixels are generally not difficult to drive. You just need a signal voltage that is relatively close to the supply voltage. We most often power them directly from 3.7v LiPo cells and control them via 3.3v processors.

A possible issue here is the output of the buck regulator. Buck converters are switch-mode regulators and typically have some residual switching noise. Some are much worse than others. And a 'dirty' power supply could cause the pixels to misbehave.

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Re: Neopixel stuck on white after reading previous forum pos

Post by mmachenry »

Are you suggesting, then, that I put a capacitor in line with the 3.7v output of the buck converter? Do you suggest any specific capacitor? The Uber guide suggests 1000 µF.

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Re: Neopixel stuck on white after reading previous forum pos

Post by adafruit_support_bill »

A filter capacitor would not be in-line. It would be in parallel. Connect the positive lead to V+ and the negative lead to GND. The ideal capacitance depends on the frequency and magnitude of the noise. But it doesn't hurt to err on the high side. 1000uF is probably a good place to start.

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Re: Neopixel stuck on white after reading previous forum pos

Post by mmachenry »

Yes in line was not the right word. Across the 3.7v + and gnd. I'll try that today. Thank you.

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Re: Neopixel stuck on white after reading previous forum pos

Post by mmachenry »

I did not have any luck with the capacitor, sadly. I installed 1000uF 10v electrolytic capacitor (NEV1000M10EE) across the 3.7v + and GND. The easiest way to do this was to pull the Trinket M0 out of the socket on my above pictured perf-board circuit, jumper BAT,GND,and PIN2 to a breadboard, with the Trinket in it, and then place the capacitor across the bat and GND pins. I saw no difference. Still stuck on white.

I am now suspicious of the wiring distances. Here's what I have. This is in a school bus roof. There are four light fixtures in the ceiling. I'm running 18/3 solid copper thermostat wire through the ceiling to each one of the light fixtures. Inside of each light fixture there's two Neopixel sticks in series chained together, the input of one going to the output of the other. I ran a wire to the nearest light fixture and wire nutted together all three wires tripplets inside the light fixture. One tripplet goes to the Trinket (3 feet), one is the Neopixel stick pair that inhabits this light fixture (1 inch) and one is going to the other fixture where there's a second pair of neopixels (3 feet away).

There was, previously, also a second set of light fixtures (four in total) that I also wired up. There was about 6 feet of wire connecting the first fixture to the trinket and then the same three feet away to it's neighbor as well. I removed these from the circuit. When I did so, the lights went from stick one being all white and stick two being white white yellow and the rest off in each of the four light fixtures to being all white in on both sticks in the two remaining fixtures. Again the program is as above. Just turns the lights red.

I'm more than happy to completely rewire this even though it would be a huge pain in the butt if it would just work. I'm not sure what's going on though.
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Re: Neopixel stuck on white after reading previous forum pos

Post by adafruit_support_bill »

Wiring distance can definitely be an issue with Neopixels. 3 feet is about the practical limit for wiring between processor and the first pixel, or from pixel to pixel. It can be less in electrically noisy environments like automotive electrical systems.

There are some ways to extend that such as line-driver buffers or 'repeater' pixels. But I'd test out your circuit with shorter wires to make sure that everything works that way first.

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