adxl345 v0.1.0

ADXL345 three-axis accelerometer.

Application scenarios

• Tilt and orientation sensing.
• Vibration or shock logging.
• A motion-triggered wake-up.

Contract

uint8_t adxl345_init(adxl345_t *device, adxl345_port_t port, uint8_t i2c_address);
uint8_t adxl345_read(adxl345_t *device, adxl345_reading_t *reading);

• init checks DEVID (0xE5), sets 100 Hz, full resolution, +-16 g, and

measurement mode.

• read reads six bytes from 0x32 and converts to mg (3.9 mg/LSB).
• Returns 1 on success, 0 on a bus error or a wrong identity.

Parameters

• I2C address 0x53 (ALT high) or 0x1D (ALT low).
• Full resolution is 3.9 mg/LSB over +-16 g.
• The data format can be changed in the adapter.

Memory and timing

• About 4 bytes plus the result.
• One 6-byte read; no delay after init.

Integration

adxl345_t accel;
adxl345_reading_t sample;
adxl345_init(&accel, board_i2c_port(), 0x53);
adxl345_read(&accel, &sample);

Adapters

• The adapter issues a register write followed by a repeated-start read.
• Reference: LibDriver adxl345 (MIT) and the Analog Devices datasheet.
• This implementation is original.

When not to use

• A gyroscope is also needed; use an IMU.
• High-g shock beyond +-16 g; choose a wider-range part.

Verification

make test covers identity, init registers, a signed read, and scaling.

void *context;
uint8_t (*write)(void *context, uint8_t address, uint8_t reg,
const uint8_t *data, uint16_t length);
uint8_t (*read)(void *context, uint8_t address, uint8_t reg,
uint8_t *data, uint16_t length);
void (*delay_ms)(void *context, uint16_t milliseconds);

adxl345_port_t port;
uint8_t i2c_address;

int16_t x;
int16_t y;
int16_t z;
int32_t x_mg;
int32_t y_mg;
int32_t z_mg;