Example: How to use SimulRPi

We will show a code example that makes use of both SimulRPi.GPIO and RPi.GPIO so you can run the script on a Raspberry Pi (RPi) or computer.

Code example

The following code blinks a LED for 3 seconds after a user presses a push button. The code can be run on an RPi or computer. In the latter case, the simulation package SimulRPi is used for displaying a LED in the terminal and monitoring the keyboard.

Script that blinks a LED for 3 seconds when a button (or the key cmd_r) is pressed

 import sys
 import time

 if len(sys.argv) > 1 and sys.argv[1] == '-s':
     import SimulRPi.GPIO as GPIO
     msg1 = "\nPress key 'cmd_r' to blink a LED"
     msg2 = "Key 'cmd_r' pressed!"
 else:
     import RPi.GPIO as GPIO
     msg1 = "\nPress button to blink a LED"
     msg2 = "Button pressed!"

 led_channel = 10
 button_channel = 17
 GPIO.setmode(GPIO.BCM)
 GPIO.setup(led_channel, GPIO.OUT)
 GPIO.setup(button_channel, GPIO.IN, pull_up_down=GPIO.PUD_UP)
 print(msg1)
 while True:
     try:
         if not GPIO.input(button_channel):
             print(msg2)
             start = time.time()
             while (time.time() - start) < 3:
                 GPIO.output(led_channel, GPIO.HIGH)
                 time.sleep(0.5)
                 GPIO.output(led_channel, GPIO.LOW)
                 time.sleep(0.5)
             break
     except KeyboardInterrupt:
         break
 GPIO.cleanup()

Add the previous code in a script named for example script.py. To run it on your computer, use the -s option like this:

$ python script.py -s

If you run it on your RPi, connect a LED to the GPIO channel 10 and a push button to the GPIO channel 17. You don’t have to add the -s option when running the script on the RPi:

$ python script.py

On your computer, you get the following:

Output for the script when it is run on a computer (blinking of the LED not shown)

$ python script.py -s

Press key 'cmd_r' to blink a LED
Key 'cmd_r' pressed!

  🛑  [10]

On your RPi, you get almost the same result without the LED shown in the terminal:

Output for the script when it is run on an RPi (the LED will blink for 3 seconds)

$ python script.py

Press button to blink a LED
Button pressed!

Note

The script can be stopped at any moment if the keys ctrl + c are pressed.

Code explanation

At the beginning of the script, we check if the -s flag was used. If it is the case, then the simulation module SimulRPi.GPIO is imported. Otherwise, the module RPi.GPIO is used:

if len(sys.argv) > 1 and sys.argv[1] == '-s':
   import SimulRPi.GPIO as GPIO
   msg1 = "\nPress key 'cmd_r' to blink a LED"
   msg2 = "Key 'cmd_r' pressed!"
else:
   import RPi.GPIO as GPIO
   msg1 = "\nPress button to blink a LED"
   msg2 = "Button pressed!"

Then, we setup the LED and button channels using the BCM mode:

led_channel = 10
button_channel = 17
GPIO.setmode(GPIO.BCM)
GPIO.setup(led_channel, GPIO.OUT)
GPIO.setup(button_channel, GPIO.IN, pull_up_down=GPIO.PUD_UP)

Finally, we enter the infinite loop where we wait for the push button (or the key cmd_r) to be pressed or ctrl + c which terminates the script immediately. If the push button (or the key cmd_r) is pressed, we blink a LED for 3 seconds, then do a cleanup of GPIO channels (very important), and terminate the script:

while True:
     try:
         if not GPIO.input(button_channel):
             print(msg2)
             start = time.time()
             while (time.time() - start) < 3:
                 GPIO.output(led_channel, GPIO.HIGH)
                 time.sleep(0.5)
                 GPIO.output(led_channel, GPIO.LOW)
                 time.sleep(0.5)
             break
     except KeyboardInterrupt:
         break
 GPIO.cleanup()