#define PULSE_PIN 45
void setup() {
    // IMPORTANT: Clear Timer/Counter Control Registers
    TCCR5A = 0;
    TCCR5B = 0;

    // Set Timer/Counter Control Registers
    TCCR5A = B00101001; // Phase and frequency correct PWM change at OCRA
    TCCR5B = B00010010; // least sig bits sets "carrier frequency" by dividing CPU clock
    //  Observation:
    //  TCCR5B = B00010010 and OCR5A = 16667 results in period of 16.70 mSec
    //  meaning OCR5A is period in uSec when TCCR5B = B00010010
    //  TCCR5B = B00010001 : OCR5A = 20000 results in period = 2.5 mSec 399.3Hz

    pinMode(PULSE_PIN, OUTPUT);
}

void setRpm(){
    //  Getting to period in uSec from rpm the long way to keep
    //  the answer in range of the data type:
    unsigned int rpm = map(pot_adc, 0, 1023, RPM_MIN, RPM_MAX);
    unsigned long period = rpm/50;
    period = 24000/period;
    period = period*50;
    //  The trigger lasts 26°, so the PW is 26/360 * period.
    dwell = period/36;
    dwell = dwell*26;
    dwell = dwell/10;

    //  OCR5A is a counter the carrier frequency counts up to,
    //  which sets output period / frequency
    //  meaning OCR5A is period in uSec when TCCR5B = B00010010
    OCR5A = period; //  OCR5A is period in uSec when TCCR5B = B00010010
    //  OCR5B is the width of the pulse. If we used floats,
    //  we could use duty cycle * period.
    OCR5B = dwell;
}

// WGM modes:
 // TCCR1A
 // Bit              7      6      5      4      3     2     1     0
 // Bit Name         COM1A1 COM1A0 COM1B1 COM1B0 ----- ----- WGM11 WGM10
 // Initial Value    0      0      0      0      0     0     0     0
 // changed to       1      1      1      1      0     0     0     1

 // TCCR1B
 // Bit            7      6      5       4        3        2        1        0
 // Bit Name       ICNC1  ICES1  -----   WGM13    WGM12    CS12     CS11     CS10
 // Initial Value  0      0      0       0        0        0        0        0
 // changed to     0      0      0       0        1        0        0        1
 // CS12,CS11,CS10 = (0,1,1) = prescaler divide by 64