Raspberry Pi Pico ー 加速度センサ（I2C通信）

• XYZ加速度データの変換
• 計測レンジ：　+/-16g
• 分解能：　13bit （+/-12bit)
• 加速度への変換：　1g／8bit(256)

import machine
import utime
import ustruct
import sys

# Constant
SENSITIVITY = 1.0 / 256 # [g/LSB]
gravity = 9.80665

# I2Cの設定
i2c = machine.I2C(0, scl=machine.Pin(17), sda=machine.Pin(16), freq=400000)

# I2Cデバイスアドレスを確認
addr = i2c.scan()
ADXL345_ADDR = 0x1d

# Register
REG_DEVID = 0x00
REG_POWER_CTL = 0x2D
REG_DATAX0 = 0x32
DEVID = 0xE5

# I2C Read/Write Functions
def reg_write(i2c, addr, reg, data):
    msg = bytearray()
    msg.append(data)
    i2c.writeto_mem(addr, reg, msg)
    
def reg_read(i2c, addr, reg, nbytes=1):
    if nbytes < 1:
        return bytearray()
    data = i2c.readfrom_mem(addr, reg, nbytes)
    return data

# Main
# Read device ID
data = reg_read(i2c, ADXL345_ADDR, REG_DEVID)
if (data != bytearray((DEVID,))):
    print("ERROR: Cound not communicate with ADXL345")
    sys.exit()
    
# Read Power Control Register
data = reg_read(i2c, ADXL345_ADDR, REG_POWER_CTL)

# Start measurement
data = int.from_bytes(data, "big")|(1<<3)
reg_write(i2c, ADXL345_ADDR, REG_POWER_CTL, data)

print("XYZ Acceleration [m/s2] with ADXL345")
utime.sleep(1.0)

while True:
    # Read X, Y, Z values (16 bits each)
    data = reg_read(i2c, ADXL345_ADDR, REG_DATAX0, 6)
    # Convert 2 bytes (little-endian) into 16-bit integer (signed)
    data_acc_x = ustruct.unpack_from("<h", data, 0)[0]
    data_acc_y = ustruct.unpack_from("<h", data, 2)[0]
    data_acc_z = ustruct.unpack_from("<h", data, 4)[0]
    # Convert to g >> m/s^2
    acc_x = data_acc_x * SENSITIVITY * gravity
    acc_y = data_acc_y * SENSITIVITY * gravity
    acc_z = data_acc_z * SENSITIVITY * gravity

    # Print measurements
    print("X: ", "{:.2f}".format(acc_x),
          "Y: ", "{:.2f}".format(acc_y),
          "Z: ", "{:.2f}".format(acc_z))
    utime.sleep(0.5)

結果

とりあえずThonnyに加速度を表示させることが出来た。机に置いてある状態でZ方向は重力加速度分を読めている。ブレッドボードを傾けるとそれぞれ+/-1gの範囲では計測できることを確認できた。

少しバラつき（ノイズ(?)）がある