Power coprocessor from rev control system

As a rookie team, we have the Rev power distribution hub. What is the recommended way to power a Raspberry Pi? We don’t see anything that looks like a 5v rail. The two options we’ve been throwing around are using a buck converter or the rio usb, neither of which seem great.

Continuing the discussion from REV Robotics - 2022 FRC Control System:

Take a look at something like this:

It’s likely just a 5V regulator in a rugged-looking package. You could also buck the PDH’s 12V down to 5V, but I’d go for simple and rugged. I have no personal experience with this particular device.

You definitely shouldn’t hijack 5V from the RIO. Besides that being potentially in violation of wiring rules, it’s not a good idea to load the RIO more than necessary.

Yeah, we’ve got plenty of buck converters that we could sturdy up. I was really hoping we were missing a hole somewhere :slight_smile:

Be careful with these regulators. Anything rated for 12v may it may not stop working under a certain voltage, typically around 8-9V (where our batteries dip regularly). I did not see a voltage input range on the page. Instead, I would use something like this with a wide input range and a USB output to make things easy:

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You could also use a L7805CV, but those are only rated up to 1.5A. Assuming you’re running the Pi with something like PhotonVision and a camera, you’ll need more power than that.

I think it specs at 3.1A

That’s the other thing that concerns me about using a straight buck converter. I know the voltage is all over the place when stuff is happening and I worry about keeping it in a range the pi is happy with.

That’s a reasonable concern. We’re using a buck on a device this year, but it’s just a Tac-light.

you might pay attention to R602.

Are you referring to the unmodified connectors? What does that even mean for a raspberry pi?

Yeah, I’m confused too. We’re not talking about batteries here. A Tac-light powered from the robot, not batteries is OK. Also, the 5v 2.5A limit is only in relation to battery packs.

I believe the OP was talking about pulling 12V from the PDH to power a Pi that needs a lower voltage level. No one is talking about using additional batteries in violation of R602 (including me).

I’m referring to powering a coprocessor (which the PI certainly is) from a separate battery pack and not trying to power it from the robot battery. At 5V, a battery that delivers 2.5 A of current gives you 12.5 W, which should be more than enough to drive the PI and a camera.

Idk if it’s against the rules but if the pi can survive on 2amps is it legal to tap from the VRM? That has a dedicated 5V 2A slot that we have used for powering an Arduino for off-season projects. That uses less power but it did work.

Edit: double checked the manual and I don’t see anything disallowing that for a valid 2A power source. If someone finds something let me know. You have to use at least 22ga wire for the power connections for that circuit per “R622 *Use appropriately sized wire.” And it’s chart that lists VRM 2A circuits

We power our RaspberryPis using PoE. If you don’t have a hat on already might be an option to look into.


Wouldn’t the POE injector still need a valid 5v source or do you also have a poe switch? We use the Rev injector for the radio power, is that the same method you mean?

My team used the VRM which has continuous duty rating of 1.5 amps. It’s just barely enough for our RPi configuration and rarely did the RPi complain about low voltage. If OPs USB devices consume significant power than get an externally powered USB hub to take some load off the RPi.

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Is it 5V you need? What about using this: Pololu - 5V, 3A Step-Up/Step-Down Voltage Regulator S13V30F5

Rev has a PoE injector that can attach to the VRM POE Injector Cable - REV Robotics

The purpose of a buck converter is to take a fluctuating input and turn it into a lower voltage efficiently. Any common buck should have no problems with our battery swings. It’s only under voltage lockouts you have to be wary of.


7805 regulators just burn off excess voltage, as do all linear regulators. So while the Pi is on, you would be burning (12-5V) * 1.5A = 10.5W, which will crisp it up pretty quickly unless you put a large heatsink on it.

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