Digital pin output problems

Forum 2005-2010 (read only) Hardware Interfacing
#1

Hello, I have a very weird problem which, after a lot of cutting bits of code out of a larger program, I have simplified down to the following code:

#include <Servo.h>

byte motorPin = 9; // ATTACHED TO A LED FOR TESTING PURPOSES
byte servoPin = 6;

Servo s;

void setup() {
//s.attach(servoPin);
}

void loop() {
analogWrite(motorPin, 255);
}

Now, the “motorPin” (named so because originally going to control a solid state relay for controlling a DC motor) is attached to an LED to check if it comes on or not.

Now, guess what, with the code as shown above, the LED turns on, no surprises there. With the:

s.attach(servoPin);

line uncommented however, the LED stays off :o

What is going on here? I have tried changing the pin numbers (moved motorPin from 9 to 10) but doesn’t solve the problem. The offending line is the servo attachment to its pin.

#2

Maybe try adding pinMode(motorPin, OUTPUT); in your setup?

If the LED stays off, it may mean the code isn't getting to your loop. Is it possible to move the motor pin to a digital pin?

#3

A comment in Servo.cpp:

Note that analogWrite of PWM on pins associated with the timer are disabled when the first servo is attached.

So, this is expected behavior. Perhaps not desired, but expected.

#4

Right, bummer but I get it now. Thanks.

P.S. solved by moving motorPin to pin 11 (leaving servo on pin 5) on Duemilanove board.

#5