Crosspost, New: Pulse-width modulation with RPIO.PWM

[metachris]

Sorry for crossposting, but I think this may be interesting for a lot of people not reading the Interfacing forum.

I'm happy to announce that RPIO now includes PWM via DMA for very precise semi-hardware PWM. RPIO.PWM supports pulses with a maximum resolution of 1µs, all 15 available DMA channels and any number of GPIO's. Since it uses the same on-board PWM module as the sound card it may interfere with sound.

RPIO.PWM is written in C (source) and includes a Python wrapper compatible with Python 2 and 3. You can find the PWM documentation at pythonhosted.org/RPIO.The easiest way to install/update RPIO is with easy_install:

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$ sudo apt-get install python-setuptools
$ sudo easy_install -U RPIO

Here is an example with oscilloscope output (GPIO 15 is the blue channel, GPIO 17 the yellow one):

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# Setup PWM.Servo with the default 20ms subcycle
from RPIO import PWM
servo = PWM.Servo()

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# Set a 4000us (4ms) pulse every 20ms for GPIO 15:
servo.set_servo(15, 4000)

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# Now a 1000us (1ms) pulse for GPIO 17:
servo.set_servo(17, 1000)

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# We can use the low-level PWM methods to add further pulses to a subcycle:
PWM.add_channel_pulse(0, 17, 200, width=100)

Feedback is much appreciated!

Links

• Source code (GPLv3): https://github.com/metachris/RPIO
• Documentation: http://pythonhosted.org/RPIO
• C source of the PWM module: https://github.com/metachris/RPIO/tree/ ... urce/c_pwm
• https://pypi.python.org/pypi/RPIO

[mattvenn]

excellent!!! Worked no problems on the only pin I tried it on.
I'll be using this in my upcoming workshops.

[DexOS]

I agree great work, thanks for coding this.

[jacksparrow]

Great work.Looks alike it's going to save me lot of time at work.

[hradec]

Brilliant matte!!!! Congratulations!!!

I was wondering if this DMA approach allows a "maximum" number of pulses, so the pulses would stop after it's reached?

If so, this method could also be used to reliably control stepper drivers, like pololu 4988 ones.

anyhow... just brilliant!!!

cheers matte...
-H

[ProudRoach]

So is it that when you divide every 20µs by the 4µs you set it to you get 5µs of a 2V current?