Important changes to forums and questions

All forums and questions are now archived. To start a new conversation or read the latest updates go to forums.mbed.com.

8 Channel PWM

Topic last updated 24 Dec 2010, by Dev Joshi. 4 replies
Dev Joshi
23 Dec 2010

Just a quick one,

I am getting ready to port an old PIC based project over the mBed and was wondering if anyone knew how to do 8 channel PWM control. I know that an mBed technically has 10 PWM out channels but four of them are hooked up to the on board LEDs. I don't really fancy de-soldering to gain access to the functionality. Does anyone know of any work around or other way of doing the implementation?

I am doing some very basic motor speed control of an array which means I need to PWM 8 channels concurrently with a base clock between 500 and 1000Hz. Is this something I can do natively with an mBed? Can you think of a device or component which would let me do it? Previously I set up my own PWM controller ICs (tiny little 8 pin PIC things, serial in one side, PWM out the other, each one with an address).

Your thoughts would be much appreciated

Cheers!

Dev

Igor Martinovski
23 Dec 2010

See http://www.maxim-ic.com/datasheet/index.mvp/id/4539

It's meant for driving LED's, but it should be usable as a general PWM driver. There are other similar solutions that offer a higher resolution PWM and I2C connectivity. You would need to come up with your own code to run it but that shoudn't be too hard since the mbed library has a good implementation of the SPI and I2C peripherals, so you're half way there..

Simon Ford
24 Dec 2010

Just for future reference/correctness, mbed has 6 pwmouts; it is just 4 can also be instead routed to the LEDs, but there are still only 6 underlying hardware pwm channels.

Of course, any digitalout can also be a pwm in software depending on requirements.

Simon

George Mamo
24 Dec 2010

>> I don't really fancy de-soldering to gain access to the functionality,,

I don't think you need to desolder the LED. You can still use your pin out !!

Dev Joshi
24 Dec 2010

Thanks for the responses guys.

 

@Igor : I did some experiments using LED drivers previously but the base frequency and a number of other things cause the results to be a little erratic. Perhaps I will revisit this in the new year.

 

@Simon: Oh I see! I mis-interpreted that then, thanks for the heads up.