I'm building a kinetic sculpture and using a MEGA 2560 to adjust spinning motor speeds. I've got a great, simple little program that I'm using to adjust the speed on the fly. I'm using a motor control module and this part has all tested out great.
/*
Mega analogWrite() test for controlling motor with Serial.
This only works with Serial input values between 0 and 255. Don't type anything else, silly.
*/
// These constants won't change. They're used to give names to the pins used:
const int motorPin = 9;
// This is where the incoming serial integers will be stored:
int incomingInt = 0;
String incomingString = "0";
void setup() {
// set pin as output:
pinMode(motorPin, OUTPUT);
Serial.begin(115200); // opens serial port, sets data rate
}
void loop() {
if ( Serial.available() > 0) {
// read the incoming serial data.
incomingString = Serial.readStringUntil('\n');
incomingInt = incomingString.toInt();
// say what you got:
Serial.print("I received: ");
Serial.println(incomingInt, DEC);
}
analogWrite(motorPin,incomingInt);
}
HOWEVER, when controlled this way, the motor gets noisy, and the environment for the sculpture will be very quiet. I tested it, and the motor runs noticeably noisier with the PWM signal than it does with the equivalent average voltage run as "straight" analog DC from a power supply.
So I had this great idea that if I can increase the frequency of the PWM outside the range of human hearing, I could still control the motor from the Arduino, but it wouldn't have the same noise produced by the audible 490Hz PWM signal going to the motor.
I'm equipped with a Digital Oscilloscope and DMM to check my work as I go. I know my wiring and setup is good because it all reads and acts as expected with the sketch above.
I found the below little snippet online to adjust the timer on the Mega, which seemed like a good approach. Except, when I inserted it into my setup section, it seems to affect the analogWrite function in an unintended way. With this modification, any number I enter into serial >= 4 gives 100% duty cycle output, and anything lower obviously won't drive the motor.
int myEraser = 7; // this is 111 in binary and is used as an eraser
TCCR2B &= ~myEraser; // this operation (AND plus NOT), set the three bits in TCCR2B to 0
int myPrescaler = 1; // this could be a number in [1 , 6]. In this case, 3 corresponds in binary to 011.
TCCR2B |= myPrescaler; //this operation (OR), replaces the last three bits in TCCR2B with our new value 011
I've also tried a couple libraries i.e. Timer1, Timer3, but even running their example sketches give me an always-on output (confirmed by my Oscilloscope) instead of a PWM signal for some reason.
Long post but hoping all the detail will help.... Thank you in advance 