esp-idf/examples/cxx/experimental/sensor_mcp9808/main/sensor_mcp9808.cpp

/* ESP MCP9808 Sensor/I2C C++ Example

   This example code is in the Public Domain (or CC0 licensed, at your option.)

   Unless required by applicable law or agreed to in writing, this
   software is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
   CONDITIONS OF ANY KIND, either express or implied.
*/

#include <iostream>
#include "i2c_cxx.hpp"

using namespace std;
using namespace idf;

#define ADDR 0x18
#define I2C_MASTER_NUM I2C_NUM_0   /*!< I2C port number for master dev */
#define I2C_MASTER_SCL_IO    19    /*!< gpio number for I2C master clock */
#define I2C_MASTER_SDA_IO    18    /*!< gpio number for I2C master data  */

#define MCP_9808_TEMP_REG 0x05

/**
 * Calculates the temperature of the MCP9808 from the read msb and lsb. Loosely adapted from the MCP9808's datasheet.
 */
float calc_temp(uint8_t msb, uint8_t lsb) {
    float temperature;
    msb &= 0x1F;
    bool sign = msb & 0x10;
    if (sign) {
        msb &= 0x0F;
        temperature = 256 - (msb * 16 + (float) lsb / 16);
    } else {
        temperature = (msb * 16 + (float) lsb / 16);
    }

    return temperature;
}

extern "C" void app_main(void)
{
    try {
        // creating master bus, writing temperature register pointer and reading the value
        shared_ptr<I2CMaster> master(new I2CMaster(I2C_MASTER_NUM, I2C_MASTER_SCL_IO, I2C_MASTER_SDA_IO, 400000));
        master->sync_write(ADDR, {MCP_9808_TEMP_REG});
        vector<uint8_t> data = master->sync_read(ADDR, 2);

        cout << "Current temperature: " << calc_temp(data[0], data[1]) << endl;
    } catch (const I2CException &e) {
        cout << "I2C Exception with error: "  << e.what();
        cout << " (" << e.error<< ")" << endl;
        cout << "Coulnd't read sensor!" << endl;
    }
}