WT61 IMU Quick Reference

6-axis IMU (accelerometer + gyroscope) with onboard angle calculation via Kalman filter.

Serial Configuration

Setting	Factory Default	Our Config
Baud rate	115200	9600
Output rate	100Hz	20Hz

Config command (send at 115200 to switch to 9600/20Hz):

0xFF 0xAA 0x64

This is saved to flash - persists across power cycles.

Wiring (ATmega328P / AltSoftSerial)

WT61 Pin	Arduino Pin	Notes
TX	8 (RX)	AltSoftSerial fixed pin
RX	9 (TX)	Only needed for config commands
VCC	5V
GND	GND

Packet Structure

11 bytes per packet, continuous stream (3 packet types interleaved):

Byte 0:    0x55 (header)
Byte 1:    Packet type
Bytes 2-3: Value 0 (int16_t, little-endian)
Bytes 4-5: Value 1
Bytes 6-7: Value 2
Bytes 8-9: Temperature (usually ignored)
Byte 10:   Checksum (sum of bytes 0-9, lower 8 bits)

Packet Types

Type	Byte 1	V0	V1	V2
Acceleration	0x51	ax	ay	az
Gyroscope	0x52	gx	gy	gz
Angle	0x53	roll	pitch	yaw

Scale Factors

Measurement	Formula	Range
Acceleration	`raw / 32768.0 * 16.0`	+/-16g
Gyroscope	`raw / 32768.0 * 2000.0`	+/-2000 deg/s
Angle	`raw / 32768.0 * 180.0`	+/-180 deg
Temperature	`raw / 340.0 + 36.25`	Celsius

Known Quirks

Boot time: Module needs ~200-500ms after power-on before sending valid data
Config at wrong baud: Commands sent at wrong baud rate are ignored (garbled bytes) - this is actually useful for idempotent config-on-boot
AltSoftSerial at 115200: Technically out of spec for 16MHz AVR, but TX-only bursts of a few bytes work fine. Don't try sustained RX at that rate.

Commands

All commands are 3 bytes: 0xFF 0xAA <data>

Data Byte	Function	Notes
0x52	Zero Z-axis angle	Resets yaw to 0
0x67	Accelerometer calibration	Keep module level, zeros X/Y
0x60	Toggle sleep mode	Toggles between standby and active
0x61	Serial mode	Enable UART, disable I2C
0x62	I2C mode	Enable I2C, disable UART
0x63	115200 baud / 100Hz	Factory default
0x64	9600 baud / 20Hz	Our config
0x65	Horizontal mounting	Module placed flat
0x66	Vertical mounting	Module placed upright

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