Hardware Schematic

Annotated walkthrough of the Waveshare LC29H GPS/RTK HAT schematic. The HAT connects the Quectel LC29H GNSS module to Raspberry Pi and Jetson Nano via the 40-pin GPIO header, with jumper-selectable UART/USB communication and onboard battery backup.

Power Supply

5V from the Pi GPIO header (pin 2/4) feeds a 3.3V LDO regulator (ME6211) that powers the LC29H module. An ML1220 rechargeable coin cell battery provides backup power to the RTC and SRAM, maintaining ephemeris data and time across main power cycles.

Note

The ML1220 battery charges when main power is applied. If the battery is depleted, cold starts will take ~26 seconds instead of ~1 second (hot start) until ephemeris data is re-acquired.

GNSS Module and RF Path

The LC29H module connects to the dual-frequency L1/L5 antenna via an IPEX 1st-gen (U.FL) connector. The integrated LNA (Low Noise Amplifier) and SAW (Surface Acoustic Wave) filter provide high sensitivity (-165 dBm tracking) with strong interference rejection.

UART Interface

The primary serial interface routes through a jumper-selectable path. When set to position B, the module’s TX/RX lines connect directly to the Raspberry Pi’s UART pins (GPIO 14/15) via level-shifting circuitry.

USB Bridge (CP2102)

When the jumper is at position A, UART traffic routes through a Silicon Labs CP2102 USB-to-UART bridge to the USB-C connector. This provides an alternative communication path independent of the GPIO UART.

I2C Interface

The module’s I2C lines (SDA/SCL) connect to the Pi’s I2C bus (GPIO 2/3) through level shifters. I2C can be used for NMEA output and command transmission as an alternative to UART.

LED Indicators

Four status LEDs provide visual feedback:

LED	Color	Function
PWR	Red	Power indicator
TX	Green	NMEA data transmission
RX	Green	Data reception from host
PPS	Blue	Pulse-per-second (position fix acquired)

Full Schematic Pages

Page 2 — Complete Circuit Diagram

Page 3 — GPIO Header and Connector Pinout