Society of Robots - Robot Forum

Electronics => Electronics => Topic started by: corrado33 on October 24, 2009, 10:02:43 AM

Title: I need four PWM outputs.... 1 or 2 micro controllers?
Post by: corrado33 on October 24, 2009, 10:02:43 AM

So as the title states, I need to drive 4 DC motors, therefore I need 4 PWM outputs.  I'm making a palm powered robot, so I don't need an overly complicated microcontroller cause most of the processing will be done by the palm. 

So should I just buy the cheapest microcontroller that has 4 PWM outputs?  Microcontrollers themselves aren't that expensive, so I really don't care.  I saw one of the higher numbered AtMega#### ones that had 4 PWM outputs.  It was 7 bucks I think?  The only problem is that it was square, and I couldn't find a socket for it.  (Yeah I suck at searching DigiKey)

So, any advice? 

Title: Re: I need four PWM outputs.... 1 or 2 micro controllers?
Post by: waltr on October 24, 2009, 10:17:24 AM

Many processors today are not designed for sockets, they are designed to be soldered to a PCB as a surface mount device. Try to find that processor on some type of breakout or development board. SparkFun has a nice selection of such boards.

PWM output can also be done with software and an internal hardware timer. Most of the time it is better to use one processor.

Title: Re: I need four PWM outputs.... 1 or 2 micro controllers?
Post by: Soeren on October 24, 2009, 10:49:24 AM

Hi,

Even an 8 pin controller can be used for that.
Make the PWM either by a timer interrupt or by simply counting through a loop setting the relevant bits on the relevant times and resetting them in the end or v.v.

Title: Re: I need four PWM outputs.... 1 or 2 micro controllers?
Post by: corrado33 on October 24, 2009, 01:22:52 PM

Gotcha, so specific PWM outputs just make PWM easier.  I understand now.  I thought PWM outputs were REQUIRED for PWM.  THANKS!!

Title: Re: I need four PWM outputs.... 1 or 2 micro controllers?
Post by: Webbot on October 27, 2009, 04:46:56 PM

Hardware PWM comes at no expense (ie it just happens) but requires the number of hardware PWM channels to be available on the chip.

You can 'simulate' PWM by using a timer to generate interrupts to call your code which then flicks the output pins. BUT - bear in mind that with slow PWM frequencies the motors will judder or whine so you need a high'ish frequency. So if you are trying to do it in software then your mcu may spend most of its time in interrupts simulating PWM