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+# MotionCal
+
+![](img/MotionCal_2026-04-25_11-22.png)
+MotionCal is a desktop magnetometer calibration utility originally written by Paul Stoffregen. This fork is maintained at:
+
+```text
+https://salemdata.net/repo/jlpoole/MotionCal
+```
+
+Upstream source:
+
+```text
+https://github.com/PaulStoffregen/MotionCal
+```
+
+The application reads IMU-style serial data, builds a 3D magnetometer point cloud, and estimates magnetic calibration parameters:
+
+```text
+hard iron offset       magnetic_offset_uT
+soft iron correction   magnetic_mapping_matrix
+field strength         magnetic_field_uT
+```
+
+This fork is being used with a LilyGO T-Beam Supreme / QMC6310 bridge firmware that streams MotionCal-compatible `Raw:` lines over USB serial.
+
+## What MotionCal Produces
+
+A saved calibration file contains values like:
+
+```text
+magnetic_offset_uT=-172.96843,43.0260162,78.8941956
+magnetic_field_uT=52.4668198
+magnetic_mapping_matrix=
+  0.943139076 0.0439298451 0.0595370531
+  0.0439298451 1.04979992 -0.0347476006
+  0.0595370531 -0.0347476006 1.01706612
+```
+
+The hard-iron offset moves the center of the magnetometer cloud back to zero. The soft-iron matrix transforms an ellipsoid-shaped cloud back toward a sphere.
+
+The correction model is:
+
+```text
+mag_uT = raw_motioncal_counts * 0.1
+centered = mag_uT - magnetic_offset_uT
+corrected = magnetic_mapping_matrix * centered
+```
+
+## Serial Input Format
+
+MotionCal expects ASCII serial lines like this:
+
+```text
+Raw:accel_x,accel_y,accel_z,gyro_x,gyro_y,gyro_z,mag_x,mag_y,mag_z
+```
+
+The T-Beam bridge firmware currently sends placeholder accelerometer and gyro values, plus live magnetometer readings:
+
+```text
+Raw:0,0,8192,0,0,0,mag_x,mag_y,mag_z
+```
+
+Example:
+
+```text
+Raw:0,0,8192,0,0,0,-1578,447,1266
+```
+
+For this workflow, the magnetometer values are MotionCal integer counts:
+
+```text
+1 count = 0.1 microtesla
+uT = counts * 0.1
+```
+
+These are not the QMC sensor's original register counts. The T-Beam bridge reads SensorLib Gauss values, converts Gauss to microtesla, then converts microtesla to MotionCal counts.
+
+## T-Beam Bridge Firmware
+
+The companion firmware project lives at:
+
+```text
+/usr/local/src/microReticulumTbeam/exercises/25_motioncal_tbeam
+```
+
+Typical bridge workflow:
+
+```sh
+source /home/jlpoole/pioenv/bin/activate
+cd /usr/local/src/microReticulumTbeam/exercises/25_motioncal_tbeam
+pio run -e dan -t upload
+pio device monitor -b 115200 --port /dev/ttytDAN
+```
+
+Close the serial monitor before opening the same port in MotionCal.
+
+## Build On Linux
+
+MotionCal uses wxWidgets and OpenGL. On this system, the working build command is:
+
+```sh
+cd /usr/local/src/MotionCal
+make WXCONFIG=wx-config LDFLAGS="-lglut -lGLU -lGL -lm"
+```
+
+If the linker cannot find OpenGL/GLUT libraries, install the development packages for wxWidgets, OpenGL, GLU, and freeglut using your distribution's package manager.
+
+The Makefile default references a local wxWidgets path:
+
+```make
+WXCONFIG = ~/wxwidgets/3.0.2.gtk2-opengl/bin/wx-config
+```
+
+Overriding `WXCONFIG=wx-config` on the make command line uses the system wxWidgets configuration instead.
+
+## Run
+
+Run the GUI with:
+
+```sh
+cd /usr/local/src/MotionCal
+GDK_BACKEND=x11 ./MotionCal
+```
+
+Then select the T-Beam USB serial port in the MotionCal window.
+
+If running under Wayland and the GUI has trouble starting or rendering, `GDK_BACKEND=x11` forces the wx/GTK path through X11 compatibility.
+
+## Calibration Procedure
+
+1. Flash and start the T-Beam bridge firmware.
+2. Confirm the serial stream contains `Raw:` lines.
+3. Close any terminal monitor using the serial port.
+4. Start MotionCal.
+5. Select the T-Beam serial port.
+6. Rotate the board through as many 3D orientations as possible.
+7. Continue until the point cloud has good sphere coverage and fit metrics are stable.
+8. Save the calibration settings from MotionCal.
+
+Good calibration requires broad 3D motion. Do not only rotate the board flat on a table. Roll, pitch, yaw, invert, and sweep through orientations so the cloud fills the sphere.
+
+## Saved Settings Files
+
+This fork includes a modified save path that writes calibration settings to timestamped text files such as:
+
+```text
+MotionCal_settings_20260425_114546.txt
+MotionCal_KitchenMagnet_settings_20260426_080729.txt
+```
+
+Saved files include:
+
+```text
+valid_points
+fit_error_percent
+surface_gap_error_percent
+magnitude_variance_error_percent
+wobble_error_percent
+magnetic_offset_uT
+magnetic_field_uT
+magnetic_mapping_matrix
+cal1_echo_line
+cal2_echo_line
+raw_points
+```
+
+The `raw_points` section is useful for later analysis because it preserves the magnetometer point cloud that produced the calibration.
+
+## Calibration Packet Echo
+
+MotionCal can send a 68-byte calibration packet back to the device. The T-Beam bridge accepts that packet and echoes human-readable values:
+
+```text
+Cal1:...
+Cal2:...
+```
+
+The `Cal1` line contains hard-iron offsets and field strength. The `Cal2` line contains the 3x3 soft-iron mapping matrix.
+
+## Interpreting Hard And Soft Iron
+
+Hard iron is a fixed magnetic bias. It shifts the center of the point cloud.
+
+Soft iron is field distortion. It stretches, squashes, shears, or rotates the cloud into an ellipsoid. MotionCal estimates an inverse soft-iron matrix that maps the ellipsoid back toward a sphere.
+
+A matrix close to identity means small soft-iron distortion:
+
+```text
+1 0 0
+0 1 0
+0 0 1
+```
+
+Example modest soft-iron correction:
+
+```text
+0.9431  0.0439  0.0595
+0.0439  1.0498 -0.0347
+0.0595 -0.0347  1.0171
+```
+
+## Troubleshooting
+
+If MotionCal does not show incoming points:
+
+```text
+Confirm the correct serial port is selected.
+Confirm the device is streaming at 115200 baud.
+Confirm the stream contains Raw: lines.
+Close pio device monitor before opening the port in MotionCal.
+```
+
+If calibration values appear 10x different from a notebook or script:
+
+```text
+MotionCal saved offsets are in microtesla.
+The Raw: magnetometer values are MotionCal counts.
+Convert counts to uT with: uT = counts * 0.1
+```
+
+If the fit is poor:
+
+```text
+Collect more orientations.
+Keep the board away from steel, magnets, speakers, motors, and high-current wiring.
+Try the calibration in a different physical location.
+Watch for read_fail or overflow messages from the bridge firmware.
+```
+
+## Repository Notes
+
+The upstream project did not include a README at the time this fork was created. This document records the local build workflow and the T-Beam/QMC6310 calibration workflow used with this fork.
+
+Generated build outputs such as `MotionCal`, `imuread`, `*.o`, debug logs, and timestamped calibration captures are local artifacts unless intentionally committed for documentation.
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