OnOff Shim Problem?

Just added OnOff Shim to RPi4 which has an adafruit GPS. Checked the connections.

The RPI will only start up when I keep the button wires held together (ie not momentary). When I do that, it then starts to shut down.

There seem to be other posts about this. Is the device faulty do you think?

The on off shim uses the following GPIO pins

If the GPS uses any of those pins (other than power and ground) that may be your issue.
How is the GPS module wired up?

The gps hat sits on top of the OffOn Shim which sits on the RPi. The OffOn Shim is soldered to a header with long pins which allows the adafruit gps header to be pushed into place. That is, the Shim is sandwiched between the gps and RPi.

My reading of the description of the Shim is that it works with Hats. Maybe not all hats?

Sorry - just got your point. Yes, they do share Pin 7.

Does that mean they cannot work together?

The two sharing pin 7, GPIO 4 is likely your issue. What does the GPS use pin 7 for?

Ah! Adafruit say: " GPS’s can output a ‘pulse per second’ for synchronizing the time. We have a breakout for this and a closed jumper that connects it to GPIO#4 - if you do not need PPS and want to use #4 for something else, just cut the little connection on the PPS PCB line."

Ok, I have an older version of the Adafruit Ultimate GPS breakout. It uses UART or a serial to USB adapter. I’ve used it both ways on a Pi. I can’t find a link to the one I have though? Only the newer version 3 one. Is that the one you have?

EDIT: You must have the hat version? Mine is a breakout that doesn’t plug directly into the Pi’s GPIO. I would cut that jumper with an exacto knife. You can always just solder it back in place if the GPS stops working.

Yes, it’s the hat version. Thanks for the advice - will give it a go.

This is mine: https://learn.adafruit.com/assets/21931

Just to confirm that your suggestion was correct - I cut the jumper and the Shim is now working perfectly. Many thanks.

It’s for a navigation system on a boat. I just need to work out how to automatically start the nav program (OpenCPN) and connect to an onboard web server which is sending out AIS signals (Yakker).

That’s good to hear, moving forward not backward. I run some python files on boot up via crontab. Many different ways to do it, that’s just what works for me.