2020 Led Wiring

Hello, I saw that this year, you can directly wire an RGB LED strip into the roboRIO(neopixel or ws2812). How would I wire this? I tried connecting all wires to the roboRIO and I also tried putting only signal into the roboRIO, and 5v and Ground into the VRM. The code should be correct, and I am on the correct PWM. Any help is greatly appreciated. Thanks in advance.

what wires do you have on the LED Strip

Just to be sure your code doesn’t cause the problem, I recommend running WPILib’s examples: Java, C++.

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Data flow on the LED strips are directional so double check that and also try the 2A ports on the VRM if you aren’t already, the 1M 60 LED strip we got from REV couldn’t do full white on just 500mA.

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We have Data In, Ground, and a 5v pins.

so I would put ground and 5v in the VRM with a “fake” ground into the rio so you have two connections points so that they don’t fall out. The data should just go into the signal of the PWM if those LEDs work with PWM. What strip are you useing

For the record, you absolutely should not use the VRM that powers your radio to power LEDs during a match. (or for that matter, anything else at all except for the radio)

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Last year we were having problems with our radio losing power. Eventually an FTA came around and found that we wired our LED driver into the VRM. I believe the VRM should only to be powering the radio and nothing else.

R47. The Wireless Bridge (Radio) power must be supplied directly by the 12V 2A output of a CTR
Electronics Voltage Regulator Module (VRM) (P/N: am-2857, 217-4245) and must be the only load
connected to those terminals.

And according to R52 you are allowed to have more than one VRM on the robot. I did not know that.

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The way I understand it, that rule is saying that the only thing that can be connected to a 12V/2A ports of any VRM is the radio. The 12V/0.5A ports and the 5V ports of the VRM can be used for anything else.

Is it possible that the LED driver was pulling more than the allowed 0.5A of current? The product page says it can support up to 15A.

I see what you’re saying. That makes a little more sense. If I remember it was connected to 12v/2A (same as radio) and it might have been pulling too much current.

So it is easily possible if for it to pull more than half an amp when the LEDs are at full power. The LED strip in question runs on 5V and you can pull some decent amperage with LEDs. The VRM sides technically share the same fuse on the PDP. so if you pull too much from the 5v rail then it is almost a sure fire thing that your radio will die along with that VRM

Also, I am not using an LED driver, but I am connecting the strand directly to the roboRIO. According to the WPI programming documentation, it should be possible to wire it directly.

I have been told that the ideal way is to connect the Data In of the Neopixels to the RIO, the V+ to the 5V/2A on the VRM, and Ground to both the RIO ground and VRM ground.

If that does not work, is your strip working at all? Try to make it run from an Arduino or similar to ensure the problem is with the RIO and not the strip.

If you have verified that the stip is functional, you should check your code. You can post it here.

@JKBear331

The LED driver @Pauls_game linked requires 12V input, and the product page says it can be powered from the main breaker, not the VRM. Of course, anything connected to the VRM should be verified to follow the current limit of the connected port.

If you are not supposed to connect anything at all to the VRM except the radio, what is the purpose of having all the ports on the VRM at all? AFAIK if you follow the current limits for the VRM and the fuse the VRM is connected to on the PDP, there should be no reason for the 12V/2A line to fail and kill the radio.

A 12v to 5v buck converter is one way to keep these kinds of loads off the VRM and avoid radio issues.

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@Doctor_Safety IF you could tell us what type of leds you are using it will help us get you to where you need to be sooner. I might have also just missed where you said it though

@JKBear331

The 0 V or ground is common to the Rio, PDB, VRM, and PCM. You don’t need to run fake ground to the Rio. If you are using a 3 pin plug, not a bad idea to put an empty socket on the 0V to help hold the plug in.

Sort of a semantic thing and I know what you mean, and the 0V is commonly referred to as the “ground” but with an isolated chassis, the robot really doesn’t have a “ground”. Even so everybody refers to the 0V as the ground… (Except maybe the British who occasionally insist on using a positive ground.) :slight_smile:

thanks.

I have a follow-up question. We are using 12 volt Leds and are planning on running them with the Neopixel library (We are assuming they will qork as the FastLed library seems to work with them correctly on an arduino.

Do you recommend powering them from the VRM, or directly from the PDP?

What happens with the VRM if one attempts to pull more current than the channel allows ( We will do the math and ensure low power, I just want to be aware and am a bit curious).

Thanks.
~Mr. R^2

Due to a previous incident (somewhere above) I will never wire anything into the VRM other than the radio. Do not risk losing radio power.

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