/*
  Sigurthr's Digispark SSTC Interrupter!
  By Matt Giordano
  
  Based heavily on ATTiny45/85 code for a simple Solid State Tesla Coil Interrupter
  By Gao Guangyan, <www.loneoceans.com/labs/>
  
  Thank you Gao!
     
  offThresh allows the user to turn off the interrupter
  by turning the potentiometer for BPS to below a certain threshold. 
  E.g. with Threshold set at 5/1023 --> 24mV, the signals will be off.
  Set Threshold to 0 for always-on operation.
  
  Digispark Physical Pinout:
    Pin 5 as Digital Input: CW/Interrupted Mode switch. 
    Pin 4 as Analog Input: Frequency. 
    Pin 3 as Analog Input: Pulse-Width.
    Pin 1 as Digital Output: LED.
    Pin 0 as Digital Output: Fiber Optic Tx.
  For the above analog inputs use a 10k Ohm pot with center wiper to associated 
  pin, one side to 5V and the other side to GND. For Pin 5 use a SPDT On/On 
  switch with center pin to Pin 5 and one side pin to ground, the other side pin to 5V.
*/    

// User Modifiable Variables Here
float maxontime = 5000;     // us - no greater than (32768/5) or 6553us!!
int offThresh = 0;          // Define (offTresh/1023 * 5)Volts as off-threshold
float duty = 0.5;           // Max Duty Cycle desired (here it's 10%)
// User Modifiable Variables End

int vpw;
int vbps;
int vcw;

int critfreq = (1000000*duty)/maxontime;  // Hertz
float ontime = 0;   // always us
float offtime = 0;  // ms or us
float freq;         // BPS Hertz
float period;       // us

int outPin = 0; 
int ledPin = 1; 
int bpsPin = 2; 
int pwPin = 3; 
int cwPin = 5;

void setup() {                
  pinMode(outPin, OUTPUT); 
  pinMode(ledPin, OUTPUT);
}

void loop() {
  vpw = analogRead(pwPin)-offThresh; // read pw voltage
  vbps = analogRead(bpsPin);       // read bps voltage
  vcw = digitalRead(cwPin);       // read cw switch state
    
  if (vcw == HIGH) {
    digitalWrite(outPin, HIGH);
    digitalWrite(ledPin, HIGH);
  }
  
  else { 
    
  if (vpw < 0){
    // Force logic low output when pw voltage is pulled low
    digitalWrite(outPin, LOW);      // Off
    digitalWrite(ledPin, LOW);      // Off
    delayMicroseconds(100);         // Short delay
  }
  
  else {
      
      freq = 1 + ((vbps+2)/2);  
      // sets max BPS to 512.
      // change to ((vbps+4)/4) for 254Hz max.
      // change to ((vbps+1)/1) for 1024Hz max.
  
      /*
        If the period becomes > 2^15 us (T = 32.768ms or f less than 30.51Hz), then
      the period variable runs over! Hence, we make sure this doesn't happen by 
      counting the numbers in milliseconds instead of microseconds. 
        Else, we can be free to count in microseconds
      */
      
      if (freq < 31){
      
        period = (1.0/freq)*1000;               // ms
        
        // Since 31 is a very low frequency, it will not exceed our 
        // pulse width at 10% duty cycle, so we just calc ontime in us.
        
        ontime = 1 + (vpw/1023.0) * maxontime;  // us
        if (ontime > maxontime){ontime = maxontime;}
        
        offtime = period - ontime/1000; // period in ms
        
        // Now send the output signals
        
        digitalWrite(outPin, HIGH);     // On
        digitalWrite(ledPin, HIGH);     // On
        delayMicroseconds(ontime);      // delay in us
        
        digitalWrite(outPin, LOW);      // Off
        digitalWrite(ledPin, LOW);      // Off
        delay(offtime);                 // delay in ms
        
      }
      
      else {
        period = (1.0/freq)*1000000;     // us
        
        if (freq > critfreq){
            ontime = 1 + (vpw/1023.0)*period*duty;    // period in us
        }   
        else{ontime = 1 + (vpw/1023.0)*maxontime;}   // period in us 
        
        // Calculate off-times, capping the on-time to some max

        if (ontime > maxontime){ontime = maxontime;}
        
        offtime = period - ontime;      // period in us
        
        // Now send the output signals in microseconds
        
        digitalWrite(outPin, HIGH);     // On
        digitalWrite(ledPin, HIGH);     // On
        delayMicroseconds(ontime);      // delay in us
        
        digitalWrite(outPin, LOW);      // Off
        digitalWrite(ledPin, LOW);      // Off
        delayMicroseconds(offtime);     // delay in us
      }
    }
  }
}