RGB Led flickers when controlled by GPIO Raspberry

Question

I found a python script to control an RGB LED with GPIO output pins from a raspberry. I connected a common cathode LED to the GPIO Pins and added a 300 ohm resistor to the ground pin. When I run the script it works quite well. I can choose the RGB values with an input in the terminal python led.py 0 100 110 for example. As long as I choose 255 0 0 - 0 255 0 - 0 0 255 it works perfectly fine. The strange thing is that when I choose for a mix of values python led.py 0 20 20 and run the code the LED starts shining. However it looks like there's a delay between de colors (red, green, blue) that are displayed, so I can sort of see how the colours are mixed. I found this very weird because I don't really use delays in my script. Someone an idea?

UPDATE: when I remove the resistor and connect the ground directly I dont get the flicker, problem is: my pcb is set in this configuration. as soon as I add a resistor for example 15 ohm I get the flicker back

I posted a video so you can see it https://www.youtube.com/watch?v=N6J5zy38j38, no it's not my camera ;)

#! /usr/bin/env python
import RPi.GPIO as GPIO
import sys
import time

# RGB LED pinnen configureren.
pinRood = 17
pinGroen = 27
pinBlauw = 22

# GPIO setup.
GPIO.setmode(GPIO.BCM)
GPIO.setwarnings(False)

# Zet de GPIO pinnen als uitgang.
GPIO.setup(pinRood, GPIO.OUT)
GPIO.setup(pinGroen, GPIO.OUT)
GPIO.setup(pinBlauw, GPIO.OUT)

# Gebruik PWM op de pinnen.
ROOD = GPIO.PWM(pinRood, 1000)
GROEN = GPIO.PWM(pinGroen, 1000)
BLAUW = GPIO.PWM(pinBlauw, 1000)
ROOD.start(0)
GROEN.start(0)
BLAUW.start(0)

if len(sys.argv) > 3:
    while True:
      # converteer de waarde 255 tot max 100 voor PWM.
      roodwaarde = (int(sys.argv[1]) * 100) / 255
      groenwaarde = (int(sys.argv[2]) * 100) / 255
      blauwwaarde = (int(sys.argv[3]) * 100) / 255

      ROOD.ChangeDutyCycle(roodwaarde)
      GROEN.ChangeDutyCycle(groenwaarde)
      BLAUW.ChangeDutyCycle(blauwwaarde)


GPIO.cleanup()

Answer 1

Don't continually call the dutycycle function. You are probably resetting its function many times per second.

Try something like

...
import time
...
if len(sys.argv) > 3:
   # converteer de waarde 255 tot max 100 voor PWM.
   roodwaarde = (int(sys.argv[1]) * 100) / 255
   groenwaarde = (int(sys.argv[2]) * 100) / 255
   blauwwaarde = (int(sys.argv[3]) * 100) / 255

   ROOD.ChangeDutyCycle(roodwaarde)
   GROEN.ChangeDutyCycle(groenwaarde)
   BLAUW.ChangeDutyCycle(blauwwaarde)

   time.sleep(1000)

For a pigpio equivalent try the following. Needs the pigpio daemon to be running (sudo pigpiod).

#! /usr/bin/env python

import sys
import time
import pigpio

# RGB LED pinnen configureren.
pinRood = 17
pinGroen = 27
pinBlauw = 22

pi = pigpio.pi()
if not pi.connected:
   exit()

if len(sys.argv) > 3:
   # max 255 voor PWM.
   roodwaarde = int(sys.argv[1])
   groenwaarde = int(sys.argv[2])
   blauwwaarde = int(sys.argv[3])

   pi.set_PWM_dutycycle(pinRood, roodwaarde)
   pi.set_PWM_dutycycle(pinGroen, groenwaarde)
   pi.set_PWM_dutycycle(pinBlauw, blauwwaarde)

   time.sleep(60)

   pi.set_PWM_dutycycle(pinRood, 0)
   pi.set_PWM_dutycycle(pinGroen, 0)
   pi.set_PWM_dutycycle(pinBlauw, 0)

pi.stop()

Answer 2

Without connection details this is unanswerable.

If you are trying to use a single resistor in the common leg it is no wonder it is unreliable as each LED has a different voltage and only the lowest (usually Red) will work.

NOTE coloured LEDs often need >3V so won't work reliably on the Pi - you may need transistors.

PS running without a current limiting resistor is likely to damage the Pi.