// Demonstration sketch only.
// Shows the structure: input -> lookup/interpolation -> correction -> output.

const byte frequencyOutputPin = 7;
const byte voltageSensePin    = A3;
const byte coilInputPin       = 6;

struct LookupPoint {
 float x;
 float y;
};

LookupPoint rpmTable[] = {
 { 300,  10.02 },
 { 700,  89.54 },
 { 800, 126.45 },
 { 900, 171.45 },
 { 1500, 225.12 }
};

const int rpmTableSize = sizeof rpmTable / sizeof rpmTable[0];

float interpolate(LookupPoint table[], int tableSize, float input, int &x) {
 for (int i = 0; i < tableSize - 1; i++) {
   if (input >= table[i].x && input <= table[i + 1].x) {
     float x0 = table[i].x;
     float y0 = table[i].y;
     float x1 = table[i + 1].x;
     float y1 = table[i + 1].y;
     x = i;
     return y0 + (y1 - y0) * (input - x0) / (x1 - x0);
   }
 }

 return 0;   // input was outside the table range
}

void setup() {
  Serial.begin(115200);
  Serial.println("\n----\n");

 pinMode(frequencyOutputPin, OUTPUT);
 pinMode(voltageSensePin, INPUT);
 pinMode(coilInputPin, INPUT);

 digitalWrite(frequencyOutputPin, LOW);
}

void loop() {
  static unsigned long cpounter;
  Serial.print(cpounter); Serial.print(" ");
  cpounter++;

 // ----- INPUT -----

  unsigned long upT, downT;
  upT = pulseIn(coilInputPin, HIGH,  100000);  // wait 0.1 seconds each
  downT = pulseIn(coilInputPin, LOW, 100000);

  if (!upT || !downT) {
    Serial.println("no pulse");
    delay(100);
    return;  // no valid pulse
  }

  // else

  unsigned long pulseTime = upT + downT;

  Serial.println(1000000.0 / pulseTime);
  delay(100);  //throttle/spem. do this right millis()-style

 

  int analogReading = analogRead(voltageSensePin);

  return;  // testing just the input section

 // ----- PROCESS -----

 float rpm = 0;


// pulse HIGH + LOW  in us
 if (pulseTime > 0) {
   rpm = 6000000.0 / pulseTime;   // demo calculation, not necessarily correct for the real tach
 }
 int where;
 float baseOutput = interpolate(rpmTable, rpmTableSize, rpm, where);

 float voltageCorrection = analogReading / 1023.0;

 int pwmOutput = baseOutput * voltageCorrection;

 pwmOutput = constrain(pwmOutput, 0, 255);


 // ----- OUTPUT -----

 analogWrite(frequencyOutputPin, pwmOutput);
 Serial.println("\n ar    bo   pt    rpm   pwm");
 Serial.print(analogReading); Serial.print("  ");
 Serial.print(baseOutput); Serial.print("  ");
 Serial.print(pulseTime); Serial.print("  ");
 Serial.print(rpm); Serial.print("  ");
 Serial.print(pwmOutput);
  Serial.print("  ("); Serial.print(where); Serial.print(") ");
 Serial.println("\n");

 delay(333);
}