PWM library help

Forum 2005-2010 (read only) Software Syntax & Programs
1

So I did some searching and couldn't find exactly what I am looking for. I want to be able to generate pwm at a certain duty cycle and frequency. To do this I would like to create a library that I can easily call upon during my current project and all my future projects to come. I am new here and apologize if I am asking a question you guys get on a daily basis (I hate those guys), but I couldn't find my answer.

So the goal is to turn a signal from a wii nunchunck into a pwm signal, with them will output to motor. I understand the math involved, but I am not sure exactly how to package it all together.
Here is what I got:

int pwmPin = 11
int hertz;
int duty;
int timeHigh;
int timeLow;
int totalTime;

void setup ()
{
  pinMode (pwmPin, OUTPUT);
}

void loop ()
{
  totalTime = 1000000 / hertz;
  duty = duty / 100;
  timeHigh = totalTime * duty;
  timeLow = totalTime - timeHigh;
  
  digitalWrite (pwmPin, LOW);
  delayMicroseconds (timeLow);
  digitalWrite (pwmPin, HIGH);
  delayMicroseconds (timeHigh);
}

Here is what I know is wrong.
duty and hertz never get assigned anything, therefore no other variables are assigned anything. To fix this I want those numbers to be inputed in this manner:
setPWM (duty, hertz)
That would be how I call upon the library.

So how do I do that?
I am ok if you don't want to type a response and you link me somewhere.

Also I am aware that some variables would be truncated. That was intentional. And I also know that I need a header file, but I will do that after I have this working.

Thanks,
Mike

2

I think you have this a bit backwards. The setup and loop functions do not go in a library.

A library defines a class that is instantiated in your sketch. Look at any of the libraries available for the Arduino for examples of how a library is structured and used.

If you want to create a library, you would have a constructor and setPWM methods. The setPWM method could have two reference arguments that defined where to store values.

If this does not make sense to you, I don't think you are ready to be creating libraries.

3

Ya I was alittle confused. I understand, what needs to be done now. I need to do some more reading. I am more familiar with java, but I will read into C which will help when I try and apply this the arduino.

Thanks,
Mike

4

This approach (using the delay function) will work fine as long as your program isn't doing anything else.

A more general approach is to set up one of the ATmega's timers to do PWM in the background. This is the approach used by the Arduino analogWrite() function.

I've written a PWM library that uses the 16-bit timer1. It is open source, and you are welcome to have a look at the code here:
http://code.google.com/p/tc4-shield/source/browse/#svn/trunk/arduinosoftware/libraries/PWM16

This library was written to provide low frequency (0.25 to 128 Hz) PWM output for controlling things like electric heaters through a solid state relay. So it is probably not exactly what you need. But it may get you started.

Jim

5

Thanks. The delay approach wont work. I didnt even think about it delaying the rest of my program. I wanted to go thus way to bypass the standard 490hz. I will take a look at ur library and see if i can repurpose it.
Thanks alot
Mike