This compiles just fine for me:
// Purpose: To produce a PWM signal output at 20Hz frequency and a duty cycle that has a minm of 15 % and max'm of 85%, the pot adjusted for any value in bewtween
// Arduino UNO board design: Has an input pot resistance value from pot wiper into pin A0 (pot has VCC from 5v pin and Ov from Grd pin). PWM signal ouput defined on pin 9
// Testing: currently using oscillosocpe on output pin 9, unloaded.
// Previous code worked at 30.5Hz, successfully varying LED brightness but frequency was too high for motor controller to work and turn the motor.
// STATUS: DOES COMPILE SUCCESSFULLY BUT NO PWM OUTPUT SIGNAL NOW PRODUCED ON PIN 9.
const byte potPin = A0; // Analog input pin that has the potentiometer wiper resistance value
const byte outPin = 9; // PWM output pin that Motor Controller) (or LED in testing) is attached to
float dutyCycle; // Defines the duty cycle, the % of the period (the cycle time) the PWM pulse is high
unsigned long period; // Defines the cycle time ( 1 / frequency) for PWM output
unsigned long lastChange; // The variable for incrementing the time through the loop
byte outState = LOW; // The variable holding the value of Hi or Lo output that is derived through the loop
void setup() {
period = 50000; // 50,000 us period, to be used to set the output signal at 20Hz frequency.
}
void loop() {
dutyCycle = map(analogRead(potPin), 0, 1023, 1500, 8500) / 10000.0; // returns 15% to 85% duty cycle range based on pot rotation reading 0-1023.
unsigned long onTime = period * dutyCycle; // defines the high duration in us.
unsigned long offTime = period * (1 - dutyCycle); // defines the low duration in us.
if (outState == HIGH) {
if (micros() - lastChange > onTime) {
outState = LOW;
lastChange += onTime;
}
else {
if (micros() - lastChange > offTime) {
outState = HIGH;
lastChange += offTime;
}
}
digitalWrite(outPin, outState);
}
}
Fixed various types in the process, and changed millis() to micros() for better resolution of your duty cycle. You have only 50 ms, so a 1 ms resolution is a bit crude. I also changed the name of signal to something that's not red coloured (I've bad experience with such red coloured names so simply avoid them).