Automation hat pin swap


#1

I’m using the UART on my Raspberry PI 3B for serial communication and need RTS/CTS functionality. I also would like to use all three relays on the automation hat. The problem comes in with CTS being mapped to BCM 16 (Pin 36 on the header) which the automation hat uses for relay 3.

Is it possible to remap relay 3 to a free GPIO? https://github.com/pimoroni/automation-hat/blob/master/library/automationhat/init.py

BCM 25 looks like a good candidate since it is conveniently brought out next to the spi pins for easy access. My next question is where would be a good spot to cut the trace connecting BCM 16 and connect the new GPIO?


#2

Ooof. that’s a tricky one. The software is easy enough to remap, but the trace much less so.

It looks like your best bet is to cut it on the top-side of the board where it via’s through from the bottom to the top. It’s the via right above the “S” and the “N” in “BSNS”.

This routes to the darlington driver (ULN2003A). You could jump a wire from the pin marked #25 on the 3V3 header to the right pin on this chip.

With the board facing you, text rightside topwise, the pin you want is the bottom right of the ULN2003A.


#3

Actually that trace also via’s through to the back of the board right before it goes into the ULN2003A. You could scrape out the via here, but it’s much harder to illustrate exactly where this via is since from the front side it’s underneath the ULN2003A chip.