Let's Make Robots!

Yet another PWM Picaxe question

Byrik

I am programming my Mr Basic with Mr Basic moron driver. I use a Picaxe 28x1. It is a very basic setup indeed, with a small servo carrying a sharp IR distance sensor.

After reading many pages of manuals and LMR and example code of other victims, I ran into a wall. It's the dreaded "PWM and servopos don't mix" wall on picaxes.

I understand from all the frustrated posts on LMR that the valid workaround would be to not mix pwm and servo commands. Use one after the other, but never simultaneously. That's were I fail. How do I switch off a servo signal or pwm signal?

My current code makes a PWM signal and the servo responds to it. The electrical signal is not to blame. Noisy as it might be. When I delete the servo commands from my code, but leave everything plugged in (servo, sharp, driver), the servo stops jittering.

I tried to bring the servopin low, to bring the pwm pin low, but neither is stopping the timer issue. Should I force the timer to OFF in between commands? Should my uC take a very short "nap"? Is there an official answer here at all?

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.
rik's picture

I am starting to understand how people would give up and just throw an extra 08M at the problem. This has been frustrating as hell so far. I am kennelijk a newbie at this picaxe timer stuff. So I started out fresh.

It would be so nice to be able to say "I recommend an extra IC for PWM because the valid workaround is such a hack". But without a proper valid workaround, all I can say now is: "Just give up before you get frustrated, like I did.".

And Mintelt.

And Oddbot.

And MarkusB.

And Fritsl.

And Chris the Carpenter.

And ...

MarkusB's picture

Don't be frustrated, that's part of electronics :)

Let's start to determinate, if electrical noise is the problem. If not, then we try to work on the program. Keep a second chip as last solution ;-)

MarkusB's picture

Hi Rik,

Quote: How do I switch off a pwm signal?

Picaxe manual 2, page 140:

"This command is different to most other BASIC commands in that the pwmout
runs continuously (in the background) until another pwmout command is sent."

"To stop pwmout on a pin it is necessary to isssue a ‘pwmout pin, off’ command."

rik's picture

Thanks Markus. Could I have missed that because I was (at the time) reading an old version of the manual? I will investigate. I'd love to blame someone else. ;-)

If I could do the same to a servo(pos) command, I'd be 100% helped.