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Eric Slaghuis avatar Ubuntu

Boot failure when powered via GPIO with UART connection to PIXHAWK 4 MINI

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Eric Slaghuis

I have a Raspberry Pi 4 4GB and connected to my PixHawk 4 Mini via UART. If I power the Raspberry PI via the USB-C port, it boots and I have good communication to the flight controller via the UART, GPIO 14 (UART TX) and GPIO 15 (UART RX). (i.e. I conclude my connection is good and the UART console has been disabled successfully). If I power the device via a 5A UBEC (See The PIHUT article) to the GPIO pins 4 and 6, the Raspberry PI does not boot. If I disconnect the UART cables, the Raspberry PI does boot (powered via the UBEC).

I tried the same on a Raspberry PI 3B and experience the same behaviour.

I run Ubuntu 20.04 LTS Server on both devices.

My first question is does the UBEC offer enough power. I would argue that it does, based on the PIHUT article, but how do I confirm it? The PixHawk 4 mini is powered via its own power supply, thus does not draw additional power from the PI.

Where do I start searching? I was thinking that I should try and enable an alternative UART to see if that maybe resolves the challenge.

I also found this article on the Raspberry Pi Forums that argues that the TTY Console detects the data from the flight controller and assumes it must be a console. (This kind of overrides me disabling the console). This however does not explain why the PI would work when powered via USB-C.

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Eric Slaghuis avatar Ubuntu
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Eric Slaghuis

I enabled UART5 on the Raspberry Pi-4, amended my wiring and code. Now it works. Does not explain the initial question, but does provide a solution.

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