Hello Kind People,

Hope everyone's well! I'm working on a Raspberry Pi driven project, which requires an ATX type power switch. The idea is to have a momentary switch drive powering up and cutting power to the Pi having gone through an orderly shutdown.

I have decided to use an Arduino UNO board to accommodate for my power button (with it's pull up resistor) and control the orderly shutdown in conjunction with a Python script on the Pi - no issues there. A small 5V relay is controlling cutting power to the Pi once a shutdown has completed.

Both the Arduino board and the Pi are powered by the same 5V 3A power supply, which I've take out of the official RPI PSU I got from Amazon.

All good so far, however I have encountered a major problem. When I power the system, my Pi is not getting enough power - I'm seeing the lightning icon in top-right corner of the screen, suggesting Pi board is not getting enough voltage. I've done some research and found that Pi requires over around 4.7V and anything else will trigger the "low power" warning. Having measured voltage on RPI board, I can see around 5.1V (although I'm aware this is an average value my meter is giving me - unfortunately I have no way of checking if there are any momentary drops in voltage).

My thoughts are following:
- Is there an issue powering both the Arduino and Raspberry Pi with the same power supply? Specifications of both boards suggest that a 3A supply should be enough, unless I'm missing something. Worth mentioning - skipping the Arduino circuit and powering RPI on its own seems absolutely fine - no low voltage warning.

Let me know if this makes sense, I'm happy to create some schematics of the whole circuit to help you understand the setup if my description is not clear.

Appreciate all your thoughts, have an awesome day!

 

- Is there an issue powering both the Arduino and Raspberry Pi with the same power supply?

None that I can think of. The only issue I see is possibly the use of the relay you mention. When the relay drops out it may give the Pi or the Arduino a headache. Next unless you power the Arduino board using the USB port the needed power to externally power the Arduino board is suggested at 7 to 12 Volts. This because when the board is powered externally it uses an on board voltage regulator. Also, as was just mentioned in another thread, this assumes a genuine Arduino board and not a Chinese clone.

Generally when an Arduino is used to drive a relay an opto-coupler is employed. This allows isolation between the uC driving the relay and the relay coil itself. This is not cast in stone anywhere and merely a suggestion.

Ron