Hardware

The LC29H GPS/RTK HAT is a 65mm x 30.5mm board that connects the Quectel LC29H dual-band GNSS module to single-board computers via the 40-pin GPIO header. This page covers every physical aspect of the board: connection methods, jumper configuration, LED behavior, GPIO mapping, power requirements, and antenna guidance.

Board dimensions (65mm × 30.5mm), mounting hole positions, and component placement. Click to view full resolution. Image: Waveshare

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Connection Methods

Three ways to connect the HAT to a host, depending on your hardware and use case.

Method	Device Path	Baud Rate	GPIO Required	Best For
HAT (direct stack)	/dev/ttyS0 (Pi 4B) or /dev/ttyAMA0 (Pi 5)	9600 default, typically configured to 115200	Yes (UART)	Raspberry Pi, Jetson Nano
USB cable	/dev/ttyUSB0	9600 default, typically configured to 115200	No	Any computer with USB
Jumper wires to GPIO	Depends on host UART device	9600 default, typically configured to 115200	Yes (wired)	Non-Pi SBCs, breadboard prototyping

HAT (Direct Stack on Pi GPIO)

The simplest method for Raspberry Pi and Jetson Nano. Stack the HAT onto the 40-pin header, set the jumper to position B, and the module communicates over the Pi’s hardware UART.

Pi 4B

The Pi 4B uses the mini UART at /dev/ttyS0 for GPIO serial by default. Enable it via raspi-config under Interface Options, then Serial Port.

Pi 5

The Pi 5 uses the PL011 UART at /dev/ttyAMA0 for GPIO serial. The device path differs from Pi 4B — double-check your configuration and scripts if migrating between boards.

USB Connection

Connect via the onboard micro-USB connector (not USB-C — see the board photo above). Set the jumper to position A. The CP2102N USB-to-UART bridge presents the module as /dev/ttyUSB0. The CP210x kernel driver is included in most modern Linux distributions.

This method requires no GPIO configuration and works with any computer that has a USB port, including laptops running Windows or macOS.

Jumper Wires to GPIO

For SBCs without a Pi-compatible 40-pin header, wire the HAT’s breakout pins directly:

HAT Pin	Connect To	Notes
TXD	Host RX pin	Module transmit to host receive
RXD	Host TX pin	Host transmit to module receive
GND	Host GND	Common ground — required
5V	Host 5V out	Or 3.3V to the 3V3 pin if 5V is unavailable

Caution

Cross-connect TX/RX: the HAT’s TXD connects to the host’s RX, and the HAT’s RXD connects to the host’s TX. This is the most common wiring mistake.

Set the jumper to position B when using wired GPIO connections, since the UART lines need to route to the header pins rather than the USB bridge.

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Jumper Settings

The yellow 3-position jumper (visible on the left side of the board) controls how the LC29H module’s UART lines are routed. The three positions are silk-screened directly on the PCB.

Position	Label on PCB	Routing	Use Case
A	USB - LC29H	Module UART routes through the CP2102N to the micro-USB connector	USB connection to any computer
B	Pi - LC29H	Module UART routes directly to the 40-pin GPIO header (GPIO 14/15)	HAT stacked on Pi or wired GPIO
C	USB - Pi	USB bridge connects to the Pi UART — the LC29H module is bypassed	Firmware update or USB-to-serial passthrough

Danger

Never place jumper caps on more than one position simultaneously. Positions A and B both drive the module’s UART lines, and connecting both creates bus contention that can corrupt data or damage the level-shifting circuitry.

Default position: The HAT ships with the jumper at position B (Pi - LC29H).

Position C explained: This is a special configuration that connects the Pi’s UART directly to the USB bridge, completely bypassing the GNSS module. It is useful for firmware update scenarios where the PC needs a serial passthrough to the module via a separate path.

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LED Indicators

Four LEDs along the top-right edge of the board provide status feedback. All LEDs are driven through 1K current-limiting resistors.

LED	Color	Behavior	Meaning
PWR	Red	Steady on	5V power is applied to the board
TXD	Green	Blinks rapidly	Module is transmitting NMEA sentences to the host
RXD	Green	Blinks on activity	Host is sending data (commands, RTCM corrections) to the module
PPS	Green	1 blink per second	Position fix acquired — the module has a valid satellite lock

Reading the PPS LED

The PPS (Pulse Per Second) output is the most important diagnostic indicator:

• Not blinking: No satellite fix. Check antenna connection, ensure clear sky view, and allow up to 26 seconds for a cold start (or up to 1 second for a hot start if the ML1220 backup battery is charged).
• Blinking once per second: Valid position fix. The module is outputting NMEA sentences with position data.
• Blinking but no position data on serial: Jumper is likely in the wrong position, or the serial port baud rate does not match. The module ships at 9600 baud; the Waveshare sample code reconfigures it to 115200.

Tip

The PPS LED is the quickest way to confirm the module has a satellite fix. If it is not blinking after a minute outdoors, check the antenna connection at the IPEX socket.

RTK Status (DA and BA Variants)

The LC29H(DA) and LC29H(BA) variants support RTK positioning. RTK fix status is not indicated by a dedicated LED on the HAT. Monitor RTK state via the GGA NMEA sentence quality indicator field: 4 = RTK Fixed (centimeter accuracy), 5 = RTK Float (decimeter accuracy).

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GPIO Pin Mapping

The HAT uses specific pins on the Raspberry Pi 40-pin header. The following table shows the complete mapping.

Primary Communication Pins

Pi Header Pin	BCM GPIO	Function	Direction	Notes
Pin 8	GPIO 14 (TXD)	UART TX to module RXD	Host to module	Pi transmit, module receive
Pin 10	GPIO 15 (RXD)	UART RX from module TXD	Module to host	Module transmit, Pi receive
Pin 3	GPIO 2 (SDA)	I2C Data	Bidirectional	4.7K pull-up to 3.3V on board
Pin 5	GPIO 3 (SCL)	I2C Clock	Host to module	4.7K pull-up to 3.3V on board

Signal and Control Pins

Pi Header Pin	BCM GPIO	Function	Direction	Notes
Pin 7	GPIO 4	PPS (Pulse Per Second)	Module to host	1 Hz pulse when fix acquired
Pin 15	GPIO 22	RESET	Host to module	Active low; 10K pull-up to 3.3V on board
Pin 11	GPIO 17	WAKEUP	Host to module	Toggles module from backup to active mode

Note

The RESET pin is active low with a 10K pull-up resistor. There is also a physical RESET button on the board (near the top-center, labeled “RESET”) that can be pressed to reset the module without software commands.

Power Pins

Pi Header Pin	Function	Notes
Pin 2 or Pin 4	5V supply	Powers the HAT via the GPIO header
Pin 1	3.3V	Not used for power input; the HAT generates its own 3.3V
Pin 6, 9, 14, 20, 25, 30, 34, 39	GND	Common ground

Breakout Header Pins

The HAT includes breakout pin headers along the top edge (visible in the board photo), providing direct access to signals for wiring or probing:

Breakout Label	Function
TXD	Module UART transmit
RXD	Module UART receive
PPS	Pulse per second output
PWR	Power indicator (active high)
DIR	Wheel tick direction input (DR variants: BA, CA)
GND	Ground
TICK	Wheel tick pulse input (DR variants: BA, CA)

Note

The DIR and TICK pins are used only by the LC29H(BA) and LC29H(CA) Dead Reckoning variants. They accept wheel speed sensor signals with ESD protection rated for inputs up to 24V (via SP0503BAHTG). For DR operation, the wheel tick sensor precision should be at least 0.05 m/tick.

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Pin Functions

Pin	Function	Description
RXD	UART Receive	Serial data from host to module
TXD	UART Transmit	Serial data from module to host
SDA	I2C Data	NMEA 0183 and command transmission via I2C
SCL	I2C Clock	I2C clock signal
WAKEUP	Wake	Toggles module from backup mode to active
PPS	Pulse Per Second	Time synchronization pulse; LED indicates positioning lock
WI/RES	Reserved	Not currently available

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Power Requirements

Supply Voltage and Current

Parameter	Value	Source
Input voltage	5V via GPIO header pin 2/4, or 5V via micro-USB	Wiki, schematic
Continuous current draw	< 40 mA at 5V	Wiki specification
Operating temperature	-40C to +85C	Wiki specification

Onboard Voltage Regulation

The HAT has two voltage regulators visible in the schematic:

• RT9193-33PB: 5V to 3.3V LDO regulator powering the digital logic and level-shifting circuitry
• RT9166-28PXL: Generates 2.8V for the LC29H GNSS module’s core supply (VDD_EXT)

The 5V input from the Pi GPIO header (or USB connector) feeds both regulators. No external regulation is needed.

Backup Battery

An ML1220 rechargeable coin cell provides backup power to the module’s RTC and SRAM. This preserves ephemeris data and time across power cycles, enabling hot starts (~1 second) instead of cold starts (~26 seconds).

The battery charges automatically when main power is applied. If the battery is fully depleted (extended storage without power), the first fix after power-up will be a cold start.

Full circuit diagram showing power supply section (bottom-left): RT9193 (3.3V), RT9166 (2.8V), and ML1220 backup battery. Click to view full resolution. Image: Waveshare schematic

Low-Power Considerations

• The module supports a backup mode activated via the WAKEUP pin. In backup mode, the module retains ephemeris data while drawing minimal current. Toggle the WAKEUP pin to return to active mode.
• For battery-powered applications, the < 40 mA draw at 5V (< 200 mW) is manageable, but refer to the Quectel LC29H datasheet for detailed power state specifications and sleep current figures.

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Antenna

Requirements

The LC29H tracks L1 + L5 dual-band GNSS signals. The antenna must support both frequency bands:

Band	Frequency	Constellations
L1	1575.42 MHz	GPS L1C/A, GLONASS L1, BeiDou B1I, Galileo E1
L5	1176.45 MHz	GPS L5, BeiDou B2a, Galileo E5a

The included antenna is an active (amplified) dual-frequency patch antenna. Using a single-band antenna will result in degraded accuracy and loss of L5 multipath rejection.

Connector

• Type: IPEX 1st generation (U.FL compatible)
• Location: Right edge of the board (labeled “GPS” in the board photo)
• ESD protection: RCLAMP0531T.TCT clamp on the RF path

Caution

IPEX connectors are rated for approximately 30 mating cycles. Avoid repeated connect/disconnect cycles. Seat the connector firmly until it clicks; a loose connection is the most common cause of “no satellite fix” issues.

Placement Guidelines

• Clear sky view: Mount the antenna with an unobstructed view of the sky. GNSS signals do not reliably penetrate buildings, dense tree cover, or vehicles with metallized windshields.
• Ground plane: For best performance, mount the antenna on a metallic surface (ground plane) of at least 70mm x 70mm. The metal surface reflects signals upward into the antenna, improving gain.
• Orientation: Mount with the antenna label/patch facing the open sky (upward). The ceramic patch element receives signals from the hemisphere above it.
• Cable length: Keep the coaxial cable between the antenna and the IPEX connector as short as possible. Every meter of cable introduces signal loss at L-band frequencies.
• Interference sources: Maintain distance from WiFi antennas, cellular radios, and switching power supplies. The LC29H includes multi-frequency interference cancellation for WiFi/5G, but physical separation is always preferable.

SMA Adapter

If your installation requires a panel-mount SMA connector or a different antenna with an SMA plug, use an IPEX-to-SMA pigtail adapter. Ensure the adapter and replacement antenna both support L1 + L5 dual-band operation.

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Schematic Overview

The HAT schematic shows the LC29H module connected through level-shifting circuitry to the Raspberry Pi GPIO header. Click the image to view at full resolution, or download the PDF.

Key sections visible in the schematic:

• Top-left: CP2102N USB-to-UART bridge and micro-USB connector (jumper position A)
• Bottom-left: Power supply — RT9193 (3.3V) and RT9166 (2.8V) LDO regulators, ML1220 backup battery
• Center: NDC7002N MOSFET level shifters (2.8V ↔ 3.3V) for UART and I2C, jumper routing (A/B/C positions)
• Right: LC29H GNSS module, IPEX antenna connector with ESD clamp (RCLAMP0531T)
• Top-center: Status LEDs (PWR, TXD, RXD, PPS) with 1K series resistors, wheel tick inputs with SP0503BAHTG ESD protection

For the full annotated walkthrough with PCB layouts and board dimensions, see Hardware Schematic.