9DoF IMU Breakout - IM19

This breakout pairs the Feyman (FMI) IM19 9DoF IMU with a board layout made for high-accuracy PNT and RTK GNSS projects. It combines MEMS sensor data with external GNSS RTK positioning information to provide precise attitude measurements and tilt compensation for survey-style workflows.

The IM19 is used in SparkPNT’s professional GNSS Flex and FP Surveyor products, supporting tilt-compensated surveying and continuous Dead Reckoning navigation. It is designed to work exclusively with RTK GNSS receivers and requires GNSS positioning data with an active “RTK Fix” status in its NMEA message; it will not operate with standard non-RTK GNSS receivers or positions such as “RTK float”, “DGPS”/“DGNSS” or “3D fix”.

To get started, feed the board NMEA GGA, GST and RMC messages at 5Hz, plus a standard Pulse-Per-Second timing signal. It outputs a proprietary NMEA ASCII GPFMI message containing the compensated position of the survey pole tip, plus Roll, Pitch and Yaw from the IMU.

The hardware is set up for flexible integration, with three UART interfaces, USB-UART access for UART1 and UART2, a locking JST connector for UART3, breadboard-compatible pads, multiple power options and a PCB footprint that matches SparkFun’s standard RTK GNSS boards for easy stacking.

Features:

• Survey-Grade Accuracy: Delivers roll and pitch measurements accurate to within 0.05 degrees.
• Tilt Compensation: Calculates a virtual digital level point at any tilt angle to reduce the need for perfectly vertical survey poles.
• Dependable Sensor Fusion: Provides continuous navigation (Dead Reckoning) even during brief GNSS signal loss.
• IM19 Inertial Measurement Unit: Built around the Feyman (FMI) IM19 IMU.
• UART support: Supports three UART interfaces.
• USB connectivity: USB connectivity via a dual-channel CH342 interface for UART1 and UART2.
• Locking JST Connection: UART3 is routed to a secure, 4-pin locking JST connector.
• Breadboard Prototyping: All three UARTs are broken out to standard pads.
• CH342 isolation: Pull the CH342_EN pad low to isolate the CH342 for direct access to UART1 and UART2.
• Stackable layout: PCB matches the footprint of standard RTK GNSS boards.
• Centred IMU placement: IM19 chip is placed exactly at the centre of the board to simplify LEVER_ARM calculations.
• PWR LED indicator: Onboard power LED indicator.
• ESD protection: Includes ESD protection.

Specifications:

• IMU: IM19 Inertial Measurement Unit
• UART interfaces: three
• USB-UART interface: dual-channel CH342 interface (UART1 & 2)
• JST connector: 4-pin locking JST connector (UART3)
• Power input: USB
• Power input: VIN (5V nominal)
• Power input: JST Pin 1 (default 3.3V; can be configured for 5V)
• Power input: 3.3V
• Breakout pad: UART (x3)
• Breakout pad: PPS signal input (required)
• Breakout pad: BOOT (for firmware upgrade)
• Breakout pad: RESET
• Breakout pad: GPIO (for external beeper)
• Breakout pad: CH342 EN (pull low to isolate the CH342)
• Breakout pad: MEAS jumper for current measurement
• Accelerometer operating range: ±8g
• Gyroscope operating range: ±1000°/s
• Accelerometer Bias: ±5mg
• Gyroscope Bias Accuracy: ±0.2°/s
• Roll/Pitch: ±0.025° (1σ)
• Heading: ±0.25° (1σ)
• RTK: + 0.3mm/tilt°, with 200cm straight pole (1σ)
• Auto Steering Yaw: 0.25° (1σ)
• Initialization: ~1s
• Required NMEA messages: GGA, GST, and RMC messages at 5Hz
• Required timing signal: Pulse-Per-Second (PPS)
• Output message: proprietary NMEA ASCII GPFMI
• PCB dimensions: 1.7-inch x 1.7-inch
• IM19 Z-origin: 1.6mm above the top surface (inside the package)
• IM19 Z-origin: 3.2mm above the bottom surface

Best suited to advanced RTK GNSS integrations, field surveying equipment and navigation projects that need tilt compensation and attitude data from a compact UART-enabled breakout.