Deeper understanding of PWM

Started by kdorsel on Feb 9, 2015 in TinyG Support. 2 replies, last activity Feb 18, 2015.

kdorsel Feb 9, 2015 #

I'm looking at using the PWM from the TinyG to control a laser. I have read the different configuration options from the wiki.

From what I understand you set the min/max phase and min/max rpm values. Can I correctly assume that the RPM range (max-min) is linearly mapped to the phase range (max-min) ? I would assume using something like so:
phase = (phase_max - phase_min)*(rmp - rpm_min) / (rpm_max - rpm_min) + phase_min

This will essentially give me my duty cycle. I can then set the switching frequency in the configs. I'm assuming the the switching based on the duty cycle will run at that frequency ?

What is the maximum supported frequency ? Are there any other non typical behavior ?

Thanks,

cmcgrath5035Staff Feb 9, 2015 #

You might benefit to read thru this thread:

https://github.com/synthetos/TinyG/issues/121

Max value for $p1frq is a good question. I ran it up to 20000Hz (20kHz), but don't see upper end undocumented. Need higher than that?

Other perhaps unexpected behavior?
Changes to $p1frq require a reset to take effect.
Changes to other parameters are best made when in M05 state (spindle off)
This does not seem to be a heavily used interface, so limited feedback so far.

kdorsel Feb 18, 2015 #

Thanks for the answer. 20 kHz is what I will be running at, so that should be fine.

I'll try and get my hands on an oscilloscope to do some testing.