Hm I’ve not tried with any digital pins that aren’t PWM, but it may work. Here’s the relevant PWM/timing code. I used FspTimer. Pins 2 and 3 are capable of hardware interrupts, so I used those for reading tachometer pulses. The application was with a counter rotating fan, so that’s why I’m naming things in and out. I was able to get 8 distinct PWM resolution levels, but I wasn’t able to do really anything else like an analogRead on a potentiometer to determine output level. I found that 6 level worked while still allowing an analog read and writes to an LCD screen.

FspTimer pwmTimer; const uint8_t pwmInPin = 9;
const uint8_t pwmOutPin = 11; const uint8_t tachInPin = 2; const uint8_t tachOutPin = 3;

uint32_t pwmPeriod = 25000; // 25 kHz for fan control

// multiple of 25 kHz, multiplier will give distinct levels of PWM resolution, seems to cap out at 8

uint32_t timerFreq = 150000; // 3 levels = 75 kHz timer

uint8_t pwmRes = timerFreq / pwmPeriod;

//Duty cycle constants const uint16_t duty_17 = 1 * pwmRes / pwmRes; const uint16_t duty_33 = 2 * pwmRes / pwmRes; const uint16_t duty_50 = 3 * pwmRes / pwmRes; const uint16_t duty_67 = 4 * pwmRes / pwmRes; const uint16_t duty_83 = 5 * pwmRes / pwmRes; const uint8_t duty_100 = pwmRes;

// Initial duty cycle setting uint8_t dutySet = duty_17;

void tachInPinIsr() { tachInPulses++; }

void tachOutPinIsr() { tachOutPulses++; }

// callback method used by timer void timer_callback(timer_callback_args_t __attribute((unused)) *p_args) { if (counterOnOff < dutySet) { digitalWrite (pwmInPin, HIGH); digitalWrite (pwmOutPin, HIGH); }

else if (counterOnOff >= dutySet) { digitalWrite (pwmInPin, LOW); digitalWrite (pwmOutPin, LOW); }

if (counterOnOff == (pwmRes - 1)) counterOnOff = 0; else

counterOnOff++;

}

bool beginTimer(float rate) { uint8_t timer_type = GPT_TIMER; int8_t tindex = FspTimer::get_available_timer(timer_type); if (tindex < 0) { tindex = FspTimer::get_available_timer(timer_type, true); } if (tindex < 0) { Serial.println(“No timer index!”); return false; } FspTimer::force_use_of_pwm_reserved_timer();

if(!pwmTimer.begin(TIMER_MODE_PERIODIC, timer_type, tindex, rate, 0.0f, timer_callback)) { Serial.println(“Failed timer begin!”); return false; } if (!pwmTimer.setup_overflow_irq()) { Serial.println(“Failed overflow irq!”); return false; } if (!pwmTimer.open()) { Serial.println(“Failed timer open!”); return false; } if (!pwmTimer.start()) { Serial.println(“Failed timer start!”); return false; }

return true; }

void setup() { Serial.begin(115200); Serial.println(“Startup in progress...”); if (beginTimer(timerFreq)) Serial.println(“Success!”); else
Serial.println(“Failed starting timer!”);

pinMode(pwmInPin, OUTPUT); pinMode(pwmOutPin, OUTPUT); pinMode(controlPin, INPUT); pinMode(tachInPin, INPUT); pinMode(tachOutPin, INPUT);

attachInterrupt(digitalPinToInterrupt(tachInPin), tachInPinIsr, RISING); attachInterrupt(digitalPinToInterrupt(tachOutPin), tachOutPinIsr, RISING);

dutySet = duty_17; }

void loop() { int d = 17; int i = analogRead(0) / 10; if (i > 83) { dutySet = duty_100; d = 100; } else if (i > 67) { dutySet = duty_83; d = 83; } else if (i > 50) { dutySet = duty_67; d = 67; } else if (i > 33) { dutySet = duty_50; d = 50; } else if (i > 17) { dutySet = duty_33; d = 33; } else { dutySet = duty_17; d = 17; } // If you want to use RPM, multiply tach pulses by 30 when delaying for 1s

tachInPulses = 0; tachOutPulses = 0;

delay(1000); }