hc04t-uart.cpp

#include <Arduino.h>
#include <SoftwareSerial.h>

SoftwareSerial SRSerial(D1, D0);

void setup() {
  Serial.begin(115200);
  SRSerial.begin(9600);
}

uint8_t sr_act = 0;
uint8_t buffer;
uint16_t data = 0;
uint8_t check = 0xFF;
uint8_t curByte = 0;
uint16_t hcc = 0;

uint16_t read_hc() {
  if(sr_act == 0) {
    SRSerial.write(0x55);
    //Serial.println("[>>] 0x55");
    sr_act++;
    data = 0;
    curByte = 0;
    return 0;
  }else{
    hcc++;
    if(hcc > 10000) {
      hcc = 0;
      sr_act = 0;
    }
    if(!SRSerial.available()) return 0;
    buffer = SRSerial.read();
    //Serial.print("[<<] 0x");
    //Serial.println(buffer, HEX);
    switch (curByte)
    {
    case 3:
      if(buffer != check) {
        Serial.println();
        Serial.print("[!!] Invalid result - Calc: 0x");
        Serial.print(check, HEX);
        Serial.print(" - Rcvd: 0x");
        Serial.print(data, HEX);
        Serial.print(" 0x");
        Serial.println(buffer, HEX);
      }else{
        //Serial.print("[II] Valid: 0x");
        //Serial.println(data);

        sr_act = 0;
        check = 0xFF;
        curByte = 0;

        return data;
      }
      break;

    case 2:
      data |= buffer;
      check += buffer;
      curByte++;
      break;

    case 1:
      data = buffer << 8;
      check += buffer;
      curByte++;
      break;

    case 0:
      if(buffer == 0xff) curByte++;
      break;
    
    default:
      return 0;
    }
    
  }
  return 0;
}

void loop() {
  uint16_t dist = 0;

  dist = read_hc();
  if(dist > 20) {
    Serial.print("[HC] ");
    Serial.println(dist);
    delay(75);
  }
}