Modulate complex signal on all gpio

Question

I need a signal at the output of the GIPO of approximately this shape.(sub-pulse in pulse)

How can this be implemented using PWM on PI? Im trying do it with RPIO,but his ancient GPIO pinout maybe not working for my Rpi 3 b+.

from RPIO import PWM
servo = PWM.Servo()
servo.set_servo(12, 10000)
PWM.add_channel_pulse(0, 12, start=200, width=2000)

Not Signal on pin. I'm confused in it and would like to try the built-in library to work with PWM, but I did not find there the possibility of sub-cycles. How else i can a signal of this form be output from different GPIO?

Errm, in your code the gpio pin is toggled every 2ms, so that is 500Hz-ish signal being generated and definitely not 1000Hz. I say 500Hz-ish because time.sleep only guarantees a minimum delay, not the maximum - with Linux not being a realtime OS, expecting sleep accuracy in the millisecond level is very optimistic. Oh and your code `time.sleep(0.1)` turns the 500Hz-ish signal off for 0.1s, not 0.01s as stated in your text. — DisappointedByUnaccountableMod, Sep 06 '17 at 06:55
BTW. If you want any sort of frequency accuracy, you might want to investigate using [PWM](http://pythonhosted.org/RPIO/pwm_py.html), rather than `time.sleep()`. — SiHa, Sep 06 '17 at 07:11
@SiHa Thanks! It's fine! If I want to get a frequency of 1 kHz and turn it off every 10 ms (frequency 100 Hz), then the GIPO 17 code should be about this `PWM.setup() PWM.init_channel(0) PWM.add_channel_pulse(0, 17, 0,10000) PWM.add_channel_pulse(0, 17, 100,1000)` or not? Please, if you can, arrange your answer as an answer, and tell us about this opportunity in more detail, with an example in this case. Maybe I misunderstood, if we added fast and slow pulsations, will the slow ones turn off the fast ones? How will this work at all? — Dmitrii, Sep 09 '17 at 08:28

score 2 · Answer 1 · answered Sep 03 '17 at 04:57

2

The documentation suggests that simply passing a list of channels as the first argument to both GPIO.setup and GPIO.output will accomplish what you are asking.

chan_list = [11,12]    # add as many channels as you want!
                       # you can tuples instead i.e.:
                       #   chan_list = (11,12)
GPIO.setup(chan_list, GPIO.OUT)
GPIO.output(chan_list, GPIO.LOW)                # sets all to GPIO.LOW

answered Sep 03 '17 at 04:57

Bill Porter

46
3

Thanks for you answer. But independently! Multithreading or coroutine maibe – Dmitrii Sep 06 '17 at 05:49

score 1 · Answer 2 · answered Sep 19 '17 at 22:04

1

I have had much better PWM experience with pigpio as compared to RPi.GPIO. Wiringpi is also good but pigpio's PWM support is much better IMO.

The documentation has a few functions for generating PWM on any pin:

http://abyz.co.uk/rpi/pigpio/python.html#set_servo_pulsewidth http://abyz.co.uk/rpi/pigpio/python.html#set_PWM_dutycycle

Do you *have* to use RPi.GPIO? I understand that this is not an exact answer, but I hope it at least points you in the right direction.

answered Sep 19 '17 at 22:04

pixeld

101
5

Please, add python code for this waveform - 5 Khz, turn off-on every 10 ms(100 Hz), turn its all on-off every 10 sec(0,1Hz). I know this library, but not understand how do this waveform. – Dmitrii Sep 20 '17 at 05:06

score 1 · Accepted Answer · answered Sep 20 '17 at 08:20

It seems, you should use code like this. Unfortunately, I have no chance to test it since I have no frequency meter or oscillograph.

import time
import pigpio

GPIO=12

pulse = []

#                          ON       OFF    MICROS
pulse.append(pigpio.pulse(1<<GPIO, 0,       5))
pulse.append(pigpio.pulse(0,       1<<GPIO, 5))
pulse.append(pigpio.pulse(1<<GPIO, 0,       5))
pulse.append(pigpio.pulse(0,       1<<GPIO, 1e7))

pi = pigpio.pi() # connect to local Pi

pi.set_mode(GPIO, pigpio.OUTPUT)

pi.wave_add_generic(pulse)

wid = pi.wave_create()

if wid >= 0:    
    pi.wave_send_repeat(wid)
    time.sleep(60)   # or another condition for stop processing
    pi.wave_tx_stop()
    pi.wave_delete(wid)

pi.stop()

Modulate complex signal on all gpio

3 Answers3