The Tinkerer

If you are looking for an easy way to control your Raspberry Pi projects, consider Python's Tkinter library. In about 20 lines of Python code, you can create a graphic program to control a Rasp Pi rover project (Figure 1). This article shows how to create a Python Tkinter application to control the Rasp Pi's General Purpose Input Output (GPIO) pins. I will also show you how to set up a desktop shortcut that you can use to easily launch the application, and I will configure a Virtual Network Computing (VNC) server so that a smartphone, tablet, or PC can control the Rasp Pi remotely.

Figure 1: Tkinter-controlled rover.

Python Tkinter Library

Tkinter [1] is bundled with the standard Rasp Pi Python installation. The base Tkinter library contains 17 different widgets that you can use for graphic applications. These widgets can be defined with customizable colors, sizes, text, and commands. There are three geometry managers (Pack, Grid, and Place) that can be used to arrange the widgets. For Rasp Pi hardware projects, I found the Grid geometry manager was a good fit. Listing 1 is a simple test program that presents two buttons in a grid and prints feedback when the buttons are pressed. (Note: Python 2.7 references the library as Tkinter, whereas Python 3 uses tkinter, lowercase). Figure 2 shows this test program with some button feedback.

Figure 2: Simple Tkinter example with feedback.

Tkinter Rasp Pi GPIO Motor Example

The Rasp Pi communicates with external hardware through its GPIO pins. These GPIO pins only support 5V connections, so relays or custom tops are required to connect to higher-powered devices. Very low-powered motors can be directly connected to Rasp Pi GPIO pins; however, it is highly recommended that you use a Rasp Pi motor top or some other protection hardware.

Different Rasp Pi tops will vary on the GPIO pins used for their motor connections. For our hardware setup, GPIO pins 19 and 21 were connected to the left and right motors. The GPIO pins are accessed in Python using the RPi.GPIO library. The RPi.GPIO library is preinstalled in the Raspbian image. Listing 2 shows the full code required to drive two motors. For this example, pins 19 and 21 are set as outputs using the GPIO.setup call. A motor function is created to turn each motor on or off. The Tkinter code was enhanced to make the buttons larger and add color. Also, the Python lambda function was used for passing the motor states. Figure 3 shows the Tkinter GPIO control program.

Figure 3: Rover controls.

Rasp Pi Shortcut

To make the project easier to access, you can place a quick launch icon or shortcut on the Rasp Pi desktop (Figure 4). To configure a shortcut, add a file to the user's $HOME/desktop directory:

nano $HOME/desktop/tk_gpio.desktop

Figure 4: Placing a shortcut on the Rasp Pi.

The name, icon, and execution command are defined inside this file (Listing 3).

Depending on how you plan to run your program, a shortcut might be enough; however, if you would like to control the project remotely, VNC is a good option.