README¶

🚧 Work-In-Progress

SimulRPi is a Python library that partly fakes RPi.GPIO and simulates some I/O devices on a Raspberry Pi (RPi).

Simulating LEDs on an RPi via a terminal

Introduction ¶

In addition to partly faking RPi.GPIO, SimulRPi also simulates these I/O devices connected to an RPi:

push buttons by listening to pressed keyboard keys and
LEDs by displaying small dots blinking on the terminal along with their GPIO pin number.

When a LED is turned on, it is shown as a small red circle on the terminal. The package pynput is used to monitor the keyboard for any pressed key.

Example: terminal output

Simulating LEDs on an RPi via a terminal

Each circle represents a blinking LED connected to an RPi and the number between brackets is the associated GPIO channel number. Here the “LED” on channel 22 toggles between on and off when a key is pressed.

Important

This library is not a Raspberry Pi emulator nor a complete mock-up of RPi.GPIO, only the most important functions that I needed for my Darth-Vader-RPi project were added.

If there is enough interest in this library, I will eventually mock more functions from RPi.GPIO. Thus, let me know through SimulRPi’s issues page if you want me to add more things to this library.

Dependencies ¶

Platforms: macOS, Linux
Python: 3.5, 3.6, 3.7, 3.8
pynput >=1.6.8: for monitoring the keyboard for any pressed key

Installation instructions ¶

Install the SimulRPi package with pip:
```
$ pip install SimulRPi
```
It will install the dependency pynput if it is not already found in your system.
Test your installation by importing SimulRPi and printing its version:
```
$ python -c "import SimulRPi; print(SimulRPi.__version__)"
```

Usage ¶

Use the library in your own code ¶

Case 1: with a `try` and `except` blocks ¶

You can try importing RPi.GPIO first and if it is not found, then fallback on the module SimulRPi.GPIO.

Case 1: with a try and except blocks¶

try:
    import RPi.GPIO as GPIO
except ImportError:
    import SimulRPi.GPIO as GPIO

# Rest of your code

The code from the previous example would be put at the beginning of your file with the other imports.

Case 2: with a simulation flag ¶

Or maybe you have a flag to tell whether you want to work with the simulation module or the real one.

Case 2: with a simulation flag¶

if simulation:
    import SimulRPi.GPIO as GPIO
else:
    import RPi.GPIO as GPIO

# Rest of your code

Script `run_examples.py`¶

The script run_examples which you have access to once you install the SimulRPi package allows you to run different code examples on your RPi or computer. If it is run on your computer, it will make use of the module SimulRPi.GPIO which partly fakes RPi.GPIO.

The different code examples are those presented in Examples and show the capability of SimulRPi.GPIO for simulating I/O devices on an RPi such as push buttons and LEDS.

Here is a list of the functions associated with each code example:

Example 1: run_examples.ex1_turn_on_led()

Example 2: run_examples.ex2_turn_on_many_leds()

Example 3: run_examples.ex3_detect_button()

Example 4: run_examples.ex4_blink_led()

Example 5: run_examples.ex5_blink_led_if_button()

List of options ¶

To display the script’s list of options and their descriptions: run_examples -h

-e

The number of the code example you want to run. It is required. (default: None)

-m

Set the numbering system used to identify the I/O pins on an RPi. (default: BCM)

-s

Enable simulation mode, i.e. SimulRPi.GPIO wil be use for simulating RPi.GPIO. (default: False)

-l

The GPIO channels to be used for LEDs. If an example only requires 1 channel, the first channel from the provided list will be used. (default: [10, 11, 12])

-b

The GPIO channel to be used for a push button. The default value is channel 20 which is associated with the keyboard key alt_r. (default: 13)

-t

Total time in seconds LEDs will be blinking. (default: 4)

-k

The name of the key associated with the button channel. The name must be one of those recognized by the module pynput. See the SimulRPi documentation for a list of valid key names: https://bit.ly/2Pw1OBe. Example: alt, cmd_r (default: alt_r)

--on

Time in seconds the LED will stay turned ON at a time. (default: 1)

--off

Time in seconds the LED will stay turned OFF at a time. (default: 1)

How to run the script ¶

Once you install the package SimulRPi (see Installation Instructions), you should have access to the script run_examples which can be called from the terminal by providing some arguments.

For example: run_examples -e 1 -s.

Let’s run the code example # 5 which blinks a LED if a specified key is pressed.

Here is the command line for blinking a LED (on channel 21) for a total of 5 seconds if the key cmd_r is pressed when the simulation package SimulRPi is used:

$ run_examples -s -e 5 -l 21 -t 5 -k cmd_r

Output:

Important

Don’t forget the flag -s (for simulation) when running the script run_examples if you want to run a code example on your computer, and not on your RPi.

Examples ¶

The examples presented thereafter will show you how to use SimulRPi to simulate LEDs and push buttons.

The code for the examples shown here can be also found as a script in run_examples.

Note

Since we are showing how to use the SimulRPi library, the presented code examples are to be executed on your computer. However, the script run_examples.py which runs the following code examples can be executed on a Raspberry Pi or your computer.

Example 1: display 1 LED ¶

Example 1 consists in displaying one LED on the GPIO channel 11. Here is the code along with the output from the terminal:

import SimulRPi.GPIO as GPIO

led_channel = 11
GPIO.setmode(GPIO.BCM)
GPIO.setup(led_channel, GPIO.OUT)
GPIO.output(led_channel, GPIO.HIGH)
GPIO.cleanup()

Output:

The command line for reproducing the same results for example 1 with the script run_examples is the following:

$ run_examples -s -e 1 -l 11

Warning

Always call GPIO.cleanup() at the end of your program to free up any resources such as stopping threads.

Example 2: display 3 LEDs ¶

Example 2 consists in displaying three LEDs on channels 10, 11, and 12, respectively. Here is the code along with the output from the terminal:

import SimulRPi.GPIO as GPIO

led_channels = [10, 11, 12]
GPIO.setmode(GPIO.BCM)
for ch in led_channels:
    GPIO.setup(ch, GPIO.OUT)
    GPIO.output(ch, GPIO.HIGH)
GPIO.cleanup()

Output:

The command line for reproducing the same results for example 2 with the script run_examples is the following:

$ run_examples -s -e 2

Example 3: detect a pressed key ¶

Example 3 consists in detecting if the key cmd_r is pressed and then printing a message. Here is the code along with the output from the terminal:

import SimulRPi.GPIO as GPIO

channel = 17
GPIO.setmode(GPIO.BCM)
GPIO.setup(channel, GPIO.IN, pull_up_down=GPIO.PUD_UP)
print("Press key 'cmd_r' to exit")
while True:
    if not GPIO.input(channel):
        print("Key 'cmd_r' pressed")
        break
GPIO.cleanup()

Output:

The command line for reproducing the same results for example 3 with the script run_examples is the following:

$ run_examples -s -e 3 -k cmd_r

Note

By default, SimulRPi maps the key cmd_r to channel 17 as can be seen from the default key-to-channel map.

See also the documentation for SimulRPi.mapping where the default keymap is defined.

Example 4: blink a LED ¶

Example 4 consists in blinking a LED on channel 20 for 4 seconds (or until you press ctrl + c). Here is the code along with the output from the terminal:

import time
import SimulRPi.GPIO as GPIO

channel = 20
GPIO.setmode(GPIO.BCM)
GPIO.setup(channel, GPIO.OUT)
start = time.time()
while (time.time() - start) < 4:
    try:
        GPIO.output(channel, GPIO.HIGH)
        time.sleep(0.5)
        GPIO.output(channel, GPIO.LOW)
        time.sleep(0.5)
    except KeyboardInterrupt:
        break
GPIO.cleanup()

Output:

The command line for reproducing the same results for example 4 with the script run_examples is the following:

$ run_examples -s -e 4 -t 4 -l 20

Example 5: blink a LED if a key is pressed ¶

Example 5 consists in blinking a LED on channel 10 for 3 seconds if the key ctrl_r is pressed. And then, exiting from the program. The program can also be terminated at any time by pressing ctrl + c. Here is the code along with the output from the terminal:

import time
import SimulRPi.GPIO as GPIO

led_channel = 10
key_channel = 20
GPIO.setmode(GPIO.BCM)
GPIO.setup(led_channel, GPIO.OUT)
GPIO.setup(key_channel, GPIO.IN, pull_up_down=GPIO.PUD_UP)
print("Press key 'ctrl_r' to blink a LED")
while True:
    try:
        if not GPIO.input(key_channel):
            print("Key 'ctrl_r' pressed")
            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()

Output:

The command line for reproducing the same results for example 5 with the script run_examples is the following:

$ run_examples -s -e 5 -t 3 -k ctrl_r

Note

By default, SimulRPi maps the key ctrl_r to channel 20 as can be from the default key-to-channel map.

See also the documentation for SimulRPi.mapping where the default keymap is defined.

Change Log ¶

0.0.1a0 ¶

In SimulRPi.GPIO, the package pynput is not required anymore. If it is not found, all keyboard-related functionalities from the SimulRPi library will be skipped. Thus, no keyboard keys will be detected if pressed or released when pynput is not installed.

This was necessary because Travis was raising an exception when I was running a unit test: Xlib.error.DisplayNameError. It was due to pynput not working well in a headless setup. Thus, pynput is now removed from requirements_travis.txt.

Eventually, I will mock pynput when doing unit tests on parts of the library that make use of pynput.
Started writing unit tests

0.0.0a0 ¶

First version
Tested code examples on different platforms and here are the results
- On an RPi with RPi.GPIO: all examples involving LEDs and pressing buttons worked
- On a computer with SimulRPi.GPIO
  
  macOS: all examples involving “LEDs” and keyboard keys worked
  
  RPi OS [Debian-based]: all examples involving only “LEDs” worked
  
  NOTE: I was running the script run_examples with ssh but pynput doesn’t detect any pressed keyboard keys even though I set my environment variable Display, added PYTHONPATH to etc/sudoers and ran the script with sudo. To be further investigated.

TODOs ¶

Run code examples involving pressing keyboard keys directly on an RPi (no ssh) and post results. High priority
In run_examples, improve timer accuracy when waiting for a LED to stop blinking or for a function to stop displaying a LED. Medium priority
Mock pynput when doing unit tests on Travis. Medium priority
Investigate further why no keyboard keys could be detected when connecting to an RPi through ssh and running the script run_examples with sudo. Low priority

Resources ¶

SimulRPi GitHub: source code
SimulRPi PyPI
Darth-Vader-RPi: personal project using RPi.GPIO for activating a Darth Vader action figure with light and sounds and SimulRPi.GPIO as fallback if testing on a computer when no RPi available

References ¶

pynput: package used for monitoring the keyboard for any pressed keys as to simulate push buttons connected to an RPi
RPi.GPIO: a module to control RPi GPIO channels