Detects and verifies both sensors by their identification registers.
Configures each sensor for a nominal 100 Hz raw output rate.
Emits framed, timestamped binary readings over the XIAO USB connection.
Maps both sensors into a shared enclosure frame and carries the metadata needed to derive calibrated readings without replacing raw data.

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.

The XIAO ESP32-C3 external antenna is installed for the upcoming BLE transport.

Sensor configuration

ADXL345: nominal 100 Hz output rate, full-resolution mode, +/-8 g. Nominal scale is 3.9 mg/LSB.
L3G4200D: nominal 100 Hz output rate, LPF2 selected with a 25 Hz cutoff, +/-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:

enclosure X =  native Y
enclosure Y = -native X
enclosure Z =  native Z

Host-side software calibration is applied after enclosure-axis mapping. Accelerometer offset and per-axis scale were measured with a six-face enclosure test. Gyroscope zero-rate bias and polarity were measured; its 17.5 mdps/LSB scale remains the nominal datasheet value. Mapped raw counts are stored directly, and sensor-native counts are reconstructed losslessly from the documented mapping. No software filtering or sensor fusion is performed yet.

The ESP32-C3 polls at exactly 100 Hz in a dedicated acquisition task, but each sensor has an independent internal sample clock. The status registers are read immediately before each XYZ read so a consumer can distinguish a fresh sample from a repeated poll and identify gyro overruns. Hardware data-ready interrupts and FIFO acquisition are deferred to the later sensor-side acquisition refinement.

Completed samples enter a 512-record RAM queue, providing 5.12 seconds of transport-stall tolerance at 100 Hz. A lower-priority output task batches up to eight records into versioned TRK1 frames, isolating acquisition from brief USB or future BLE stalls. CRC, packet and sample sequences, timestamps, and cumulative loss/overrun counters make loss detectable.

Measured end-to-end framing overhead is about 2.47 kB/s at 100 Hz, or 8.47 MiB/hour before BLE link overhead.

Build and flash

ESP-IDF 6.0.2 is installed at:

/Users/jay/.espressif/v6.0.2/esp-idf

For each new terminal:

source /Users/jay/.espressif/v6.0.2/esp-idf/export.sh
idf.py build
idf.py -p /dev/cu.usbmodem1134101 flash

USB output

After readable startup metadata, the device emits framed binary. Each sample is a 20-byte record containing mapped raw sensor counts, timing, sequence, and the two raw status bytes. See the complete wire-format specification.

Binary is the authoritative capture format. The host tools render it back to the same diagnostic CSV schema used during calibration:

sequence,poll_timestamp_us,accel_x_raw,accel_y_raw,accel_z_raw,gyro_x_raw,gyro_y_raw,gyro_z_raw,accel_x_mg,accel_y_mg,accel_z_mg,gyro_x_mdps,gyro_y_mdps,gyro_z_mdps,accel_native_x_raw,accel_native_y_raw,accel_native_z_raw,gyro_native_x_raw,gyro_native_y_raw,gyro_native_z_raw,accel_int_source,gyro_status,loop_overrun_count

poll_timestamp_us is reconstructed from each frame's base timestamp and 10 us record deltas. It represents the ESP32-C3 monotonic time immediately before status and data reads. It is not the sensors' physical sample time. The axes in the first six sample columns use the enclosure frame above. Calibrated acceleration is in integer milligravity (mg), and bias-corrected angular rate is in integer millidegrees per second (mdps). Native columns remain available for diagnostics.

Status bits:

accel_int_source & 0x80: an unread ADXL345 sample existed when status was checked. If clear, treat the following sample as stale/untrusted; a sample can arrive in the short interval between the status and data transactions.
accel_int_source & 0x01: ADXL345 unread data was overwritten.
gyro_status & 0x08: L3G4200D sample is fresh.
gyro_status & 0x80: L3G4200D data overran before it was read.
loop_overrun_count: cumulative acquisition deadlines missed; the loop resynchronizes after a miss instead of issuing catch-up bursts.

The binary capture tool auto-detects a single /dev/cu.usbmodem* device, stores only CRC-valid frames, renders CSV, and reports packet, sample, timing, status, drop, and overrun totals:

python tools/capture_binary.py

An existing .trk stream can be decoded again without hardware:

python tools/decode_binary.py captures/session.trk captures/session.csv

tools/capture_serial.py remains available only for decoding captures from the older CSV-v3 firmware snapshots.