mlx90614.tc

MLX90614 Infrared Non-Contact Thermometer Driver

Source on GitHub

// MLX90614 Infrared Non-Contact Thermometer Driver
// I2C address: 0x5A, no initialization needed
// Reads object temperature (0x07) and ambient temperature (0x06)
// SMBus protocol: LSB-first, 3 bytes per read (LSB, MSB, PEC)
// PEC = CRC-8 with polynomial 0x07

#define MLX_ADDR   0x5A
#define MLX_TA     0x06
#define MLX_TOBJ1  0x07

float mlx_obj = 0.0;
float mlx_amb = 0.0;
int mlx_ok = 0;
int mlx_addr = 0;
int mlx_bus = 0;

char mlx_buf[6];

// CRC-8 for SMBus PEC (polynomial 0x07, init 0x00)
int mlx_crc8(int start, int len) {
    int crc = 0;
    int i = 0;
    while (i < len) {
        crc = crc ^ mlx_buf[start + i];
        int bit = 0;
        while (bit < 8) {
            if (crc & 0x80) {
                crc = (crc << 1) ^ 0x07;
            } else {
                crc = crc << 1;
            }
            crc = crc & 0xFF;
            bit++;
        }
        i++;
    }
    return crc;
}

// Read 16-bit value from register with PEC verification
// Returns raw value or -1 on error
int mlx_read16(int reg) {
    if (!i2cReadRS(mlx_addr, reg, mlx_buf, 3, mlx_bus)) {
        return -1;
    }

    int lsb = mlx_buf[0];
    int msb = mlx_buf[1];
    int pec = mlx_buf[2];

    // Build PEC check buffer: [addr_W, reg, addr_R, LSB, MSB]
    mlx_buf[0] = mlx_addr << 1;        // address + write bit
    mlx_buf[1] = reg;                   // register
    mlx_buf[2] = (mlx_addr << 1) | 1;  // address + read bit
    mlx_buf[3] = lsb;
    mlx_buf[4] = msb;

    int cpec = mlx_crc8(0, 5);
    if (cpec != pec) {
        return -1;  // CRC mismatch
    }

    int raw = lsb | (msb << 8);
    if (raw & 0x8000) {
        return -1;  // error flag
    }
    return raw;
}

int mlx_scan() {
    int bus = 0;
    while (bus < 2) {
        if (i2cSetDevice(MLX_ADDR, bus)) {
            mlx_addr = MLX_ADDR;
            mlx_bus = bus;
            i2cSetActiveFound(mlx_addr, "MLX90614", mlx_bus);
            return 1;
        }
        bus++;
    }
    return 0;
}

void EverySecond() {
    if (!mlx_addr) {
        if (!mlx_scan()) { mlx_ok = 0; return; }
    }

    // Read object temperature (register 0x07)
    int raw = mlx_read16(MLX_TOBJ1);
    if (raw < 0) {
        mlx_ok = 0;
        return;
    }
    mlx_obj = (float)raw * 0.02 - 273.15;

    // Read ambient temperature (register 0x06)
    raw = mlx_read16(MLX_TA);
    if (raw < 0) {
        mlx_ok = 0;
        return;
    }
    mlx_amb = (float)raw * 0.02 - 273.15;

    mlx_ok = 1;
}

void WebCall() {
    char buf[64];
    if (mlx_ok) {
        sprintf(buf, "{s}MLX90614 Object{m}%.1f °C{e}", mlx_obj);
        webSend(buf);
        sprintf(buf, "{s}MLX90614 Ambient{m}%.1f °C{e}", mlx_amb);
        webSend(buf);
    } else {
        webSend("{s}MLX90614{m}no data{e}");
    }
}

void JsonCall() {
    if (!mlx_ok) return;
    char buf[96];
    sprintf(buf, ",\"MLX90614\":{\"OBJTMP\":%.1f", mlx_obj);
    responseAppend(buf);
    sprintf(buf, ",\"AMBTMP\":%.1f}", mlx_amb);
    responseAppend(buf);
}

void OnExit() {
    if (mlx_addr) {
        I2cResetActive(mlx_addr, mlx_bus);
        mlx_addr = 0;
    }
}

int main() {
    char buf[48];
    mlx_ok = 0;
    mlx_addr = 0;

    if (mlx_scan()) {
        sprintf(buf, "MLX90614 found at 0x%x on bus %d", mlx_addr, mlx_bus);
        addLog(buf);
    } else {
        addLog("MLX90614 not found");
    }
    return 0;
}