[Bug]: Heltec V4: GPS_EN polarity inverts when 3rd Party GPS pin is defined #8310
Description
Category
Hardware Compatibility
Hardware
Other
Is this bug report about any UI component firmware like InkHUD or Meshtatic UI (MUI)?
- Meshtastic UI aka MUI colorTFT
- InkHUD ePaper
- OLED slide UI on any display
Firmware Version
2.7.12.45f15b8 Alpha
Description
It looks like the Heltec V4 behaves differently from previous boards when you define your own GPS pins. On older boards, PIN_GPS_EN followed the expected polarity. Enabling the GPS would supply power, and disabling it would cut power.
On the V4, however, that logic is reversed once you override the default GPS pin. For example, I’m connecting an ATGM336H using a standard N-channel MOSFET setup — the same configuration that works correctly on all our other nodes. But on this board, enabling the GPS actually cuts power, and disabling it turns power on.
This inversion creates a compatibility problem because it breaks existing GPS modules and transistor/MOSFET power-control circuits that previously worked without changes. It appears Heltec is using a P-channel MOSFET design, which is inherently less efficient since it requires power to keep the GPS off. Reverting this behavior globally could break how their own GPS works, but there should be a way to restore the original polarity automatically if a pin other than 34 (the default) is used. That would preserve compatibility with standard N-channel setups while keeping Heltec’s design intact.