lis3dh_i2c.c

/**
 * Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

#include <stdio.h>
#include <string.h>
#include "pico/stdlib.h"
#include "pico/binary_info.h"
#include "hardware/i2c.h"

/* Example code to talk to a LIS3DH Mini GPS module.

   This example reads data from all 3 axes of the accelerometer and uses an auxillary ADC to output temperature values.

   Connections on Raspberry Pi Pico board, other boards may vary.

   GPIO PICO_DEFAULT_I2C_SDA_PIN (On Pico this is 4 (physical pin 6)) -> SDA on LIS3DH board
   GPIO PICO_DEFAULT_I2C_SCK_PIN (On Pico this is 5 (physical pin 7)) -> SCL on LIS3DH board
   3.3v (physical pin 36) -> VIN on LIS3DH board
   GND (physical pin 38)  -> GND on LIS3DH board
*/

// By default this device is on bus address 0x18

const int ADDRESS = 0x18;
const uint8_t CTRL_REG_1 = 0x20;
const uint8_t CTRL_REG_4 = 0x23;
const uint8_t TEMP_CFG_REG = 0xC0;

#ifdef i2c_default

void lis3dh_init() {
    uint8_t buf[2];

    // Turn normal mode and 1.344kHz data rate on
    buf[0] = CTRL_REG_1;
    buf[1] = 0x97;
    i2c_write_blocking(i2c_default, ADDRESS, buf, 2, false);

    // Turn block data update on (for temperature sensing)
    buf[0] = CTRL_REG_4;
    buf[1] = 0x80;
    i2c_write_blocking(i2c_default, ADDRESS, buf, 2, false);

    // Turn auxillary ADC on
    buf[0] = TEMP_CFG_REG;
    buf[1] = 0xC0;
    i2c_write_blocking(i2c_default, ADDRESS, buf, 2, false);
}

void lis3dh_calc_value(uint16_t raw_value, float *final_value, bool isAccel) {
    // Convert with respect to the value being temperature or acceleration reading 
    float scaling;
    float senstivity = 0.004f; // g per unit

    if (isAccel == true) {
        scaling = 64 / senstivity;
    } else {
        scaling = 64;
    }

    // raw_value is signed
    *final_value = (float) ((int16_t) raw_value) / scaling;
}

void lis3dh_read_data(uint8_t reg, float *final_value, bool IsAccel) {
    // Read two bytes of data and store in a 16 bit data structure
    uint8_t lsb;
    uint8_t msb;
    uint16_t raw_accel;
    i2c_write_blocking(i2c_default, ADDRESS, &reg, 1, true);
    i2c_read_blocking(i2c_default, ADDRESS, &lsb, 1, false);

    reg |= 0x01;
    i2c_write_blocking(i2c_default, ADDRESS, &reg, 1, true);
    i2c_read_blocking(i2c_default, ADDRESS, &msb, 1, false);

    raw_accel = (msb << 8) | lsb;

    lis3dh_calc_value(raw_accel, final_value, IsAccel);
}

#endif

int main() {
    stdio_init_all();
#if !defined(i2c_default) || !defined(PICO_DEFAULT_I2C_SDA_PIN) || !defined(PICO_DEFAULT_I2C_SCL_PIN)
#warning i2c/lis3dh_i2c example requires a board with I2C pins
    puts("Default I2C pins were not defined");
#else
    printf("Hello, LIS3DH! Reading raw data from registers...\n");

    // This example will use I2C0 on the default SDA and SCL pins (4, 5 on a Pico)
    i2c_init(i2c_default, 400 * 1000);
    gpio_set_function(PICO_DEFAULT_I2C_SDA_PIN, GPIO_FUNC_I2C);
    gpio_set_function(PICO_DEFAULT_I2C_SCL_PIN, GPIO_FUNC_I2C);
    gpio_pull_up(PICO_DEFAULT_I2C_SDA_PIN);
    gpio_pull_up(PICO_DEFAULT_I2C_SCL_PIN);
    // Make the I2C pins available to picotool
    bi_decl(bi_2pins_with_func(PICO_DEFAULT_I2C_SDA_PIN, PICO_DEFAULT_I2C_SCL_PIN, GPIO_FUNC_I2C));

    float x_accel, y_accel, z_accel, temp;

    lis3dh_init();

    while (1) {
        lis3dh_read_data(0x28, &x_accel, true);
        lis3dh_read_data(0x2A, &y_accel, true);
        lis3dh_read_data(0x2C, &z_accel, true);
        lis3dh_read_data(0x0C, &temp, false);

        // Display data 
        printf("TEMPERATURE: %.3f%cC\n", temp, 176);
        // Acceleration is read as a multiple of g (gravitational acceleration on the Earth's surface)
        printf("ACCELERATION VALUES: \n");
        printf("X acceleration: %.3fg\n", x_accel);
        printf("Y acceleration: %.3fg\n", y_accel);
        printf("Z acceleration: %.3fg\n", z_accel);

        sleep_ms(500);

        // Clear terminal 
        printf("\e[1;1H\e[2J");
    }
#endif
    return 0;
}