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Powering FRC/Romi

I am connecting a high-current draw USB device to the RPi on my Romi. This is causing the AA batteries to draw down in no time.

Is there a way of powering the Romi from an external source for benchtop testing?


I wonder if it would be easier to power the Pi from an external source.

I too was concerned about depleting the AA battery supply.
I ask the same question and was informed that you can solder a power wire to the BAT1+ lug close to the ON/OFF switch and a ground wire on a pin hole. I used the one next to the ON/OFF switch but ran the wire from the bottom of the board. I connected a bench power supply that I can set limits on current and voltage. I ran the power supply at 7.5 Volts and limited the current to 1 amp. It works fine. I did try to connect a 7.5 volt power supply to the USB connector and promptly fried my Raspberry PI. I ordered a SHENZHEN Universal adapter connected it to the BAT1+ terminal and the GND,
set it at 6 Volts and that works as well. Just don’t use the USB connector on the 32U4. I do not use the Batteries while connected to a power supply. Not sure whether it would damage the batteries.

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I wondered about that. Can I simply supply power to the Pi through its USB-C power connector? Looking at the controller schematic, there’s an ideal diode circuit between 5V (the controller’s regulated 5V) and RP5V (the GPIO 5V pin). So, I assume that if the Pi is powered externally, having it drive the 5V GPIO pins won’t hurt anything.

Anyone want to disagree/correct me? :slight_smile:


Full disclosure, I am figuring all this out as well, but the manual seems to be quite clear about this and seems to agree with you.

Raspberry Pi power

By default, the control board will provide power from its 5V line to an attached Raspberry Pi. In this situation, we recommend switching on the power circuit so that the Raspberry Pi receives power from the batteries through the control board’s on-board switching regulator. Alternatively, you can use a USB wall power adapter to supply power through the control board’s USB connector, although we have sometimes observed AVR brown-out resets occurring when a board powers the Raspberry Pi this way. A typical computer USB port might not be able to supply enough current to properly power the Romi 23U4 Control Board and an attached Raspberry Pi.

Power provided to the Raspberry Pi can be switched off by driving the Raspberry Pi shutdown pin, RPISHDN, to 5 V.

An ideal diode circuit on the control board makes it safe to have a different power supply connected to the Raspberry Pi (for example, through the Raspberry Pi’s USB Micro-B receptacle) while the control board is connected and powered. (In other words, it is safe to have any combination of control board USB power, battery power, and Raspberry Pi USB power connected to the system.) The RPI5V pin provides direct access to the Raspberry Pi’s 5 V line, which will typically come from the higher of the two power sources. The 3.3 V output of the Raspberry Pi is also made available on the RPI3V3 pin.

Note that the diode circuit prevents power from being shared in the reverse direction: the Raspberry Pi cannot supply 5 V logic power to the control board through the 40-pin connector.

I think it may be easier to access the power jack of an RPI 3 while attached to the Romi than an RPI 4, but I am not positive.

I have powered a Pi and the Romi Control board straight through the ROmi USB port to great success. This is a wonderful way to troubleshoot and test network tables (which are a bit fussy in this device due to the fact we run it through the simulator).

I’d bet one of these would work in getting power to a Pi 4:





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It looks like you guys have things mostly figured out, but I thought I’d clarify a few things:

  • Yes, you can connect an external power supply between BAT1+ and GND; you can also connect to VBAT, which is the same as BAT1+ and is available along with GND on 0.1"-spaced through holes nearby. This is the same place the batteries are normally connected, so you should be careful never to connect an external supply while batteries are installed to avoid shorting two different power sources together.
  • If my understanding is correct, the RPi 3B+ and 4 seem to have removed the ideal diode circuit preventing reverse current from flowing out of the USB micro-B or USB C port, so there is some risk that the Romi’s 5V supply could backfeed a USB adapter connected to the RPi if they are both connected. So if you want to power the Raspberry Pi through USB, it would be best to do this while the Romi’s main power is off or disconnected. (We will look into updating the Romi documentation.)
  • You definitely should not connect more than 5V to the USB port (either the one on the Romi or the one on the RPi).


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