modified to integrate with Motion_Cal & Magnetometer_Calibration
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# Exercise 25: MotionCal T-Beam Bridge
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Streams the T-Beam Supreme QMC6310 magnetometer in the ASCII format accepted by
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Paul Stoffregen's MotionCal desktop tool.
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This PlatformIO project turns a LilyGO T-Beam Supreme into a serial bridge for Paul Stoffregen's MotionCal desktop calibration tool.
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https://github.com/PaulStoffregen/MotionCal.git (fetch)
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The firmware reads the onboard QMC magnetometer through SensorLib and streams MotionCal-compatible ASCII `Raw:` lines over USB serial. MotionCal can then estimate both hard-iron offsets and the soft-iron correction matrix for the board.
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See https://github.com/PaulStoffregen/MotionCal/issues/25 for Gentoo build tricks.
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## Hardware
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MotionCal expects:
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Target board:
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```text
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LilyGO T-Beam Supreme / ESP32-S3
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QMC6310/QMC5883-family magnetometer
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SH1106 OLED display
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```
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The firmware probes these magnetometer I2C addresses:
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```text
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0x1C QMC6310U
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0x3C QMC6310N
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0x2C QMC5883P
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```
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The default PlatformIO environment is `cy`, with additional board labels available in `platformio.ini`:
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```text
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amy bob cy dan ed flo guy
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```
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## Serial Format
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MotionCal expects lines in this format:
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```text
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Raw:accel_x,accel_y,accel_z,gyro_x,gyro_y,gyro_z,mag_x,mag_y,mag_z
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```
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This exercise only has a magnetometer, so it sends a stationary accelerometer
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placeholder and zero gyro:
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This bridge only has a magnetometer, so it sends fixed placeholder accel/gyro values:
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```text
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Raw:0,0,8192,0,0,0,mag_x,mag_y,mag_z
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```
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The magnetic values are converted from SensorLib Gauss readings into MotionCal's
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integer units where 1 count is 0.1 microtesla.
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The placeholder values mean:
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```text
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accel = 0,0,8192 approximately stationary upright in MotionCal's count convention
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gyro = 0,0,0 no gyro data supplied
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mag = live QMC magnetometer data
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```
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## Magnetometer Units
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SensorLib returns QMC magnetometer readings in Gauss. The firmware converts them like this:
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```text
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1 gauss = 100 microtesla
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MotionCal count = microtesla * 10
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1 MotionCal count = 0.1 microtesla
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```
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So a streamed value like this:
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```text
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Raw:0,0,8192,0,0,0,-1735,428,793
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```
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means:
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```text
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X = -1735 counts = -173.5 uT = -1.735 gauss
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Y = 428 counts = 42.8 uT = 0.428 gauss
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Z = 793 counts = 79.3 uT = 0.793 gauss
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```
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These are MotionCal-compatible integer counts, not raw QMC register values.
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## Build
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Activate the Python environment that contains PlatformIO:
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```sh
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cd /usr/local/src/microreticulum/microReticulumTbeam/exercises/25_motioncal_tbeam
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source /home/jlpoole/rnsenv/bin/activate
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source /home/jlpoole/pioenv/bin/activate
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```
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Build the default environment:
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```sh
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cd /usr/local/src/microReticulumTbeam/exercises/25_motioncal_tbeam
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pio run
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```
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Build a specific board label:
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```sh
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pio run -e dan
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```
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## Upload
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Upload the default environment:
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```sh
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source /home/jlpoole/rnsenv/bin/activate
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source /home/jlpoole/pioenv/bin/activate
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cd /usr/local/src/microReticulumTbeam/exercises/25_motioncal_tbeam
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pio run -t upload
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```
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Use a specific board environment if needed:
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Upload a specific board label:
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```sh
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pio run -e guy -t upload
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pio run -e dan -t upload
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```
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## MotionCal
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## Serial Monitor
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Build and run MotionCal as before:
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After flashing, monitor the USB serial stream at 115200 baud:
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```sh
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pio device monitor -b 115200 --port /dev/ttytDAN
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```
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Expected boot/status output includes lines like:
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```text
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exercise=Exercise 25 MotionCal T-Beam bridge
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serial_format=Raw:accel_x,accel_y,accel_z,gyro_x,gyro_y,gyro_z,mag_x,mag_y,mag_z
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mag_units=MotionCal integer counts, 1 count = 0.1 uT
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magnetometer_init=ok label=QMC6310U addr=0x1C chip=0x..
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```
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Expected streaming output looks like:
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```text
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Raw:0,0,8192,0,0,0,-1578,447,1266
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Raw:0,0,8192,0,0,0,-1583,438,1258
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Raw:0,0,8192,0,0,0,-1585,442,1250
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```
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If the firmware prints `read_fail` or `overflow` status lines, check I2C wiring/power and the configured magnetometer full-scale range.
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## Running MotionCal
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Build MotionCal if needed:
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```sh
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cd /usr/local/src/MotionCal
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make WXCONFIG=wx-config LDFLAGS="-lglut -lGLU -lGL -lm"
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```
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Run it:
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```sh
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cd /usr/local/src/MotionCal
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GDK_BACKEND=x11 ./MotionCal
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```
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Select the T-Beam USB serial port in MotionCal. The firmware also accepts
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MotionCal's 68-byte calibration packet and echoes `Cal1:` and `Cal2:` lines so
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MotionCal can confirm the send.
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Then select the T-Beam USB serial port in MotionCal.
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Move and rotate the T-Beam through as many orientations as possible. The goal is to cover the sphere well, not just wave it flat on the table. Better 3D coverage improves both hard-iron and soft-iron calibration.
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## Saving Calibration
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MotionCal computes:
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```text
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magnetic_offset_uT hard-iron offset, in microtesla
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magnetic_mapping_matrix inverse soft-iron correction matrix
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magnetic_field_uT fitted local field magnitude
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```
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Example:
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```text
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magnetic_offset_uT=-172.96843,43.0260162,78.8941956
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magnetic_field_uT=52.4668198
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magnetic_mapping_matrix=
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0.943139076 0.0439298451 0.0595370531
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0.0439298451 1.04979992 -0.0347476006
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0.0595370531 -0.0347476006 1.01706612
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```
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The firmware also accepts MotionCal's 68-byte calibration packet and echoes `Cal1:` and `Cal2:` lines so MotionCal can confirm the send.
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## Applying Calibration
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MotionCal's calibration model is:
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```text
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mag_uT = raw_motioncal_counts * 0.1
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centered = mag_uT - magnetic_offset_uT
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corrected = magnetic_mapping_matrix * centered
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```
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Hard iron moves the center of the magnetometer cloud back to zero. Soft iron transforms the ellipsoid-shaped cloud back toward a sphere.
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## Troubleshooting
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If MotionCal does not show points:
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```text
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Confirm the serial port is correct.
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Confirm baud is 115200.
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Confirm monitor output contains Raw: lines.
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Close any serial monitor before opening the port in MotionCal.
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```
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If the values look 10x different from a notebook or script:
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```text
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The notebook/script may be using MotionCal counts.
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MotionCal's saved magnetic_offset_uT is already in microtesla.
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Convert counts to uT with: uT = counts * 0.1
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```
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If the fit is poor:
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```text
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Collect more orientations.
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Rotate around all axes.
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Keep the board away from steel, speakers, motors, magnets, and high-current wiring.
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Try a different location and repeat the calibration.
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```
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