Raspberry Pi 3 PWM

Question

I want to make a 120kHz PWM signal from my raspberry pi 3. Since it uses a 1,2gHz CPU. I tried using RPi.GPIO.PWM(Chanel, frequency), the max frequency I got was about 8kHz. How can I come up to 120kHz?

score 2 · Answer 1 · edited Dec 17 '18 at 19:02

2

I'm not sure that you can reach 120kHz with software PWM. That would require a wakeup every 8µs or so.

Use hardware PWM, e.g. my pigpio provides http://abyz.me.uk/rpi/pigpio/python.html#hardware_PWM and http://abyz.me.uk/rpi/pigpio/python.html#hardware_clock

edited Dec 17 '18 at 19:02

Community

1

answered Sep 04 '16 at 10:40

joan

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score 1 · Answer 2 · edited Aug 31 '17 at 19:51

The RPi module has only software PWM, and you get 8 kHz with default priority. With something like this:

sudo chrt -f 99 python3 test_pwm.py

I got a bit more then 60 kHz. Using RPi.GPIO.output, rather then PWM, I got 264 kHz.

Notes

at max frequency, the pulse width is stuck at 50%
with 2 PWM signals, the max frequency is around 40 kHz and phase varies from -145° to 100°
don't use sleep/wait for timing (it's increasing the uncertainty), make a loop with a simple instruction (e.g. var=0)
hardware PWM is said to have the base frequency at 19.2 MHz...

Raspberry Pi 3 PWM

2 Answers2