VRM and Sensors to Robo Rio

We are looking to power LEDs off of the VRM and use an Ardunio to control them over I2C. Two questions, what happens if you put too many LEDs on the VRM and it draws more than 2amps? Does the VRM and the RoboRio share the same ground plane, for I2C communication, or do they need to be tied together?

Thank you

In theory, if you draw over 2A* you will trip the current protection inside the VRM which will turn off that bank and leave the other three banks working. In practice though, I’ve seen overcurrents take down the whole VRM, either by burning it up or tripping the (non-resetting) external breaker in the PDP. That then takes down your radio too, leaving the robot dead for the rest of the match. For this reason, I recommend that teams use a cheap buck-boost converter like this on a PDP branch circuit to power peripheral electronics and leave the VRM just for the radio.

I haven’t used I2C communication with the roboRIO, so I can’t answer the second question absolutely. I would imagine that all of the grounds on the robot are common to the battery ground. It can’t hurt to tie them together just in case though.

*at 5V of course, because the 12V/2A ports are only for the radio

Ok I will plan on powering the Arduino and the LEDs off of the same 20Amp branch of the PDP and wiring the SDA and SLA to the Arduino. If they ground planes are not the same, will it hurt to pull a ground from the RoboRio to the Arduino, which would tie it to the PDP.

Make sure you have a voltage converter/regulator between the PDP and Arduino/LEDs. The PDP voltage will be anywhere between 8-13V during the course of a normal match (and even down to 5V with a bad battery/improper gearing). Arduinos and LEDs won’t be happy with that.

I’ll let a real electrical engineer answer that. I just play one on tv.

I know the PDP will have irregular voltages. I plan on wiring the LEDS then testing them with a power supply to look at the current draw before we hook them up to anything. That way I can see the assumed current draw.

I2C is very finicky on the Rio. You will need a separate ground to the Rio from the arduino preferably directly into the I2C ground pin.

You should use an off-the-shelf voltage regulator with a higher capacity. I’m a fan of this one.