Arduino sketch to interface Hella OPS+T sensor

hella_oil_sensor.ino

// HELLA OPS+T Combined digital sender (Oil pressure and temperature in one package)
// Usage: look at setup() and loop().

// Settings
const byte          hella_pin = 2;      // Pin to connect Hella OPS+T to (must be 2 or 3 on regular Arduino)
const byte          hella_count = 16;   // Number of time samples to capture - higher number for higher precision but lower refreshrate

// Variables
volatile uint32_t   hella_measured[hella_count];
volatile uint8_t    hella_num = 0;
volatile uint8_t    hella_finished = 0;

// Containers for result
uint8_t             hella_state = 0;
float               hella_temp = 0.0;
float               hella_pres = 0.0;

void setup() {
  pinMode(hella_pin, INPUT);

  Serial.begin(115200);
}

void loop() {
  hellaStart();
  hellaProcess();
  hellaPrintOut();
  delay(1000);
}

void hellaStart() {
  hella_num = 0;
  hella_finished = 0;
  attachInterrupt(digitalPinToInterrupt(hella_pin), hellaInterrupt, FALLING);
  
  while(hella_finished == 0) {}
}

void hellaInterrupt() {
  hella_measured[hella_num] = micros();
  
  // little magic to ensure that first captured edge will always be falling
  if(hella_num == 1) {
    attachInterrupt(digitalPinToInterrupt(hella_pin), hellaInterrupt, CHANGE);  
  }
  
  hella_num++;
  
  if(hella_num == hella_count) {
    detachInterrupt(digitalPinToInterrupt(hella_pin));
    hella_finished = 1;
  }
}

void hellaProcess() {
  // Compute widths of pulses  
  uint32_t widths[8];
  for(uint8_t i = 2; i < hella_count; i = i + 2) {
    widths[i / 2] = hella_measured[i + 1] - hella_measured[i];
  }

  // Compute periods of pulses
  uint32_t periods[8];
  for(uint8_t i = 1; i < (hella_count/2 - 1); i++) {
    periods[i] = hella_measured[2*i+2] - hella_measured[2*i];
  }

  // Find the first pulse
  uint8_t starter = 0;
  for(uint8_t i = 1; i < (hella_count/2 - 1); i++) {
    if((periods[i] > 950) && (periods[i] < 1150)) {
      starter = i;
      break;
    }
  }

  // Compute state
  uint32_t state = widths[starter] * 1024 / periods[starter];

  // Compute temperature pulse length
  uint32_t temp_digital = widths[starter+1] * 4096 / periods[starter+1];

  // Compute pressure pulse length
  uint32_t pres_digital = widths[starter+2] * 4096 / periods[starter+2];
  //Serial.println(pres_digital);

  // Recompute to final float vaules
  float temp = (temp_digital - 128) / 3840.0 * 200.0 - 40.0;
  float pres = (pres_digital - 128) / 3840.0 * 10.0 + 0.5;  
}

void hellaPrintOut() {
  // Print out the results
  Serial.print(temp);
  Serial.write(" degC\n");
  Serial.print(pres);
  Serial.write(" bar\n");  
}