Auto power-on the SIM868 module via its PWRKEY GPIO line

Root-caused a "GPS not working" report to the SIM868 module chip being
fully powered off (the HAT's 5V rail can be live while the chip itself
stays off until PWRKEY is triggered) - confirmed by getting zero AT
response at any baud rate while the app's GPS thread had the serial
port open normally.

Discovered this specific HAT revision has the "P4" GPIO power-on mod
wire installed (Waveshare FAQ / GSM_PWRKEY.rar script), letting PWRKEY
be triggered via physical pin 7 (BCM GPIO4) instead of a manual button
press. Verified live: pulsing it low for 4s then high brought the
module from zero AT response to responding immediately.

modules/app_gps.py: added _module_responds()/_pulse_pwrkey()/
_ensure_module_powered(), wired into _poll_loop() before the existing
GNSS power-on check. Checks AT first and only pulses PWRKEY if the
module isn't already responding, since PWRKEY is a toggle (pulsing an
already-on module would turn it back off).

Also fixed a related logging gap found while debugging: print()
diagnostics from app_gps.py were invisible in yaris-obd.log for
months because Python fully-buffers stdout when it isn't a TTY.
deploy/yaris-obd.service now sets PYTHONUNBUFFERED=1.

requirements.txt: added RPi.GPIO.
PLAN.md: documented both findings and the Pi deploy gotchas (systemd
unit file changes need a manual copy + daemon-reload; requirements.txt
changes need a manual venv pip install - neither is picked up by a
plain git pull + restart).

Co-authored-by: Copilot <[email protected]>

This commit is contained in:

Mathieu Moran

2026-08-09 15:14:28 -04:00

co-authored by

Copilot

parent e4b0823ec2

commit fc18f71cfe

4 changed files with 102 additions and 4 deletions

									
										deploy/yaris-obd.service
									
		+4
		
												View File
												
				@@ -8,6 +8,10 @@ Type=simple

				User=yaris

				Group=yaris

				WorkingDirectory=/home/yaris/app/yaris-obd

				# Unbuffered stdout so print() diagnostics (GPS/GNSS status, etc.) actually reach

				# the log file promptly instead of sitting in Python's stdout buffer indefinitely

				# when it's redirected to a file instead of a TTY.

				Environment=PYTHONUNBUFFERED=1

				ExecStart=/home/yaris/app/yaris-obd/venv/bin/python app.py

				Restart=on-failure

				RestartSec=5