checkpoint: working sensor acquisition and axis validation

README.md

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+# Trikke Motion Telemetry Logger
+
+Prototype v0 firmware for a Seeed Studio XIAO ESP32-C3 with an ADXL345
+accelerometer and L3G4200D gyroscope on a shared I2C bus.
+
+This milestone does four things:
+
+1. Detects and verifies both sensors by their identification registers.
+2. Configures each sensor for 100 Hz raw acquisition.
+3. Emits timestamped, sensor-native raw readings over the XIAO USB connection.
+4. Maps both sensors into a shared enclosure coordinate frame for validation.
+
+BLE transport and phone-side storage come after the wired sensor path is proven.
+
+## Wiring
+
+| Signal | XIAO pin | ESP32-C3 GPIO |
+| --- | --- | --- |
+| SDA | D4 | GPIO6 |
+| SCL | D5 | GPIO7 |
+| Sensor power | 3V3 | — |
+| Sensor ground | GND | — |
+
+Both breakouts share SDA, SCL, 3V3, and GND. The firmware checks both possible
+7-bit I2C addresses for each device:
+
+- ADXL345: `0x53` or `0x1D`; expected `DEVID` is `0xE5`.
+- L3G4200D: `0x69` or `0x68`; expected `WHO_AM_I` is `0xD3`.
+
+## Sensor configuration
+
+- ADXL345: 100 Hz output rate, full-resolution mode, +/-8 g. Nominal scale is
+  3.9 mg/LSB.
+- L3G4200D: 100 Hz output rate, 25 Hz bandwidth, +/-500 dps. Nominal scale is
+  17.5 mdps/LSB.
+
+The enclosure coordinate frame is:
+
+- +X points right in the reference photograph.
+- +Y points toward the top of the enclosure.
+- +Z points out of the board toward the enclosure cover.
+
+The L3G4200D already matches that frame. The ADXL345 mapping is:
+
+```text
+enclosure X =  native Y
+enclosure Y = -native X
+enclosure Z =  native Z
+```
+
+No calibration, filtering, or sensor fusion is performed yet.
+
+## Build and flash
+
+ESP-IDF 6.0.2 is installed at:
+
+```text
+/Users/jay/.espressif/v6.0.2/esp-idf
+```
+
+For each new terminal:
+
+```sh
+source /Users/jay/.espressif/v6.0.2/esp-idf/export.sh
+idf.py build
+idf.py -p /dev/cu.usbmodem1134101 flash monitor
+```
+
+Exit the serial monitor with `Ctrl-]`.
+
+## USB output
+
+After startup metadata, records use CSV:
+
+```text
+sequence,timestamp_us,accel_x_raw,accel_y_raw,accel_z_raw,gyro_x_raw,gyro_y_raw,gyro_z_raw,accel_native_x_raw,accel_native_y_raw,accel_native_z_raw,gyro_native_x_raw,gyro_native_y_raw,gyro_native_z_raw
+```
+
+`timestamp_us` is the ESP32-C3 monotonic microsecond timer since boot. The axes
+in the first six sample columns use the enclosure frame above. The appended native
+columns are temporary diagnostics for the coordinated orientation test.