[engolling]

As promised here some more information about the laser range meter.
Attached you can find a protocol overview.

The following code sends the request to the laser device:

Code:

 //Define laser measurement on USART2 #define LASER_POWER_PIN 25 #define LASER_START_PIN 24 #define LASER_HEIGHT 1986 #define LASER_LATENCY 1999 //time for laser to answer in ms int16_t laser_distance_array[SNOW_ARRAYSIZE] = { -200, -200, -200, -200, -200, -200, -200, -200, -200, -200, -200, -200}; uint8_t laser_distance_array_ind = 0; uint8_t laser_wd; uint32_t LaserReqtime; uint8_t LaserFlag = 0; union laser_send_data_t {   struct bytes_t {     uint8_t preamble;     uint8_t command;     uint8_t data[3];     uint8_t check_code[2];   } bytes;   uint8_t array[sizeof(bytes)]; } laser_send_data; union laser_rcv_data_t {   struct bytes_t {     uint8_t preamble;     uint8_t command;     uint8_t result;     uint8_t data[3];     uint8_t check_code[2];   } bytes;   uint8_t array[sizeof(bytes)]; } laser_rcv_data; pinMode(LASER_POWER_PIN, OUTPUT);  pinMode(LASER_START_PIN, OUTPUT);  digitalWrite(LASER_POWER_PIN, HIGH);  digitalWrite(LASER_START_PIN, HIGH);  delay(50);  digitalWrite(LASER_START_PIN, LOW);  laser_send_data.bytes.preamble = 0xAA;  laser_send_data.bytes.command = 0x03;  Serial2.begin(38400);

Code:

  //Read distance with laser ---- data is retrieved at the end of callback_10s   laser_send_data.bytes.check_code[0] = (uint8_t)(laser_send_data.bytes.preamble + laser_send_data.bytes.command + laser_send_data.bytes.data[0] + laser_send_data.bytes.data[1] + laser_send_data.bytes.data[2]) << 8;   laser_send_data.bytes.check_code[1] = (uint8_t)(laser_send_data.bytes.preamble + laser_send_data.bytes.command + laser_send_data.bytes.data[0] + laser_send_data.bytes.data[1] + laser_send_data.bytes.data[2]);   Watchdog.reset(); //Reset global watchdog, just to make sure that it won't get trapped   Serial2.write(laser_send_data.array, sizeof(laser_send_data.array));   LaserReqtime = millis();   LaserFlag = 1;   //Check laser watchdog reset condition - if watchdog is not resetted within the data retrieving section reboot the laser distance sensor   if (laser_wd < 5) {     laser_wd++;   }   else {     digitalWrite(LASER_POWER_PIN, LOW);     delay(100);     digitalWrite(LASER_POWER_PIN, HIGH);     digitalWrite(LASER_START_PIN, HIGH);     delay(50);     digitalWrite(LASER_START_PIN, LOW);     laser_wd = 0;   }

After 2 seconds the results are polled from the uart rx buffer

Code:

///////////////////////////////////////////////////////////////////////////////// //////// Read values of laser distance sensor via USART 2 /////////////////////// ///////////////////////////////////////////////////////////////////////////////// void read_laser(void) {  //Get data of Laser distance measurement  Watchdog.reset(); //Reset global watchdog, just to make sure that it won't get trapped  //Try to get data from serial 2  if (Serial2.available() >= 8) {    laser_wd = 0;//Reset Watchdog of laser meter if data is received - device is resettet after 5 sending counts without an answer    //Get data from buffer    Serial2.readBytes(laser_rcv_data.array, sizeof(laser_rcv_data.array));    //Calculate checksum    uint16_t checksum = 0;    for (uint8_t i = 0; i < sizeof(laser_rcv_data.array) - 2; i++) {      checksum = checksum + laser_rcv_data.array[i];    }    //Calculate distance if command, result and checksum is ok    if ((laser_rcv_data.bytes.command == 0x03) && (laser_rcv_data.bytes.result == 0x06) && (checksum == (laser_rcv_data.bytes.check_code[0] << 8 | laser_rcv_data.bytes.check_code[1]))) {      int32_t distance_temp = ((int32_t)(laser_rcv_data.bytes.data[0] << 16) | (int32_t)(laser_rcv_data.bytes.data[1] << 8) | (int32_t)laser_rcv_data.bytes.data[2]);      if (distance_temp < 32000 && distance_temp > -1) {        laser_distance_array[laser_distance_array_ind] = (int16_t)distance_temp;        //Serial.println(laser_distance_array[laser_distance_array_ind]);      }      //Move array pointer      if (laser_distance_array_ind < SNOW_ARRAYSIZE) {        laser_distance_array_ind++;      }      else {        laser_distance_array_ind = 0;      }    }    //If laser answers with wrong values    /*      else {      laser_distance_array[laser_distance_array_ind] = -100;      //Serial.println(laser_distance_array[laser_distance_array_ind]);      //Move array pointer      if (laser_distance_array_ind < SNOW_ARRAYSIZE) {        laser_distance_array_ind++;      }      else {        laser_distance_array_ind = 0;      }      }    */    uint32_t uart_timeout = millis();    //Flush serial buffer if something is left for any reason and protect from endless looping    while (Serial2.available() > 0 && (millis() - uart_timeout < 500)) {      Serial2.read();      //Serial.println("Empty Buffer");    }  } }

To make it better the answer should be, as already described, received with an interrupt routine.