Simulate Raspberry Pi add-on hardware

Soft Pi

© Lead Image © Author, 123RF.com

© Lead Image © Author, 123RF.com

Article from Issue 230/2020
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Python and tk_tools let you create software versions of Raspberry Pi mini-displays, LED keypads, and NeoPixel hardware.

Raspberry Pis have some great hardware options for displaying information or accepting input. You can use either specialty plates that mount directly on top of the Rasp Pi or a variety of wired components.

Although nothing beats using real hardware for projects, if you're missing the hardware or you'd like to duplicate a value remotely, then a soft version of the hardware can be very useful. In this article, I look at three examples of hardware simulated with the help of Python and the tk_tools Python library [1]: a seven-segment wired display, an LCD keypad, and a NeoPixel string.

Seven-Segment Display

A seven-segment display uses seven horizontal and vertical bars, familiar in clocks, meters, and other electronic devices, to represent numbers and letters. The displays are often based on the HT16K33 [2] or TM1637 [3] chipset (Figure 1).

Figure 1: HT16K33 (left) and TM1637 (right) seven-segment displays.

The tk_tools Python library [1] contains a soft component for a seven-segment display that can save you writing code from scratch. To install the module, enter:

pip install tk_tools

The tk_tools seven-segment component can function like a TM1637 or HT16K33 display component, with support for various heights, digit colors, and background color. Listing 1 is an example that displays the Rasp Pi's CPU temperature (Figure 2). After creating the seven-segment display object (line 8), simply call set_value (line 18) to display the updated Pi temperature value.

Listing 1

Show Pi CPU Temperature

 

Figure 2: Simulated seven-segment display.

LCD Keypad

LCD keypad plates [4] have five or six configurable buttons and a 2x16-character LCD display. These keypads are ideal in small projects for which you want some local control. My daughters and I have used the LCD keypad plates on a number of Pi projects, such as FM radios (Figure 3) and streaming music players.

Figure 3: LCD keypad used on a Raspberry Pi FM radio project.

The tk_tools library doesn't have an LCD keypad component, but I found that it is easy to simulate with the standard Python Tkinter library. For my example, I tried to replicate the look and feel of the Pi plate that I had, but you could enhance or change it to meet your requirements.

Listing 2 is a Python LCD keypad example that displays key presses (Figure 4). Lines 13-17 create a single label with white on blue text. The grid's rowspan and columnspan properties (line 18) create a label two lines high that spans the entire window. The label automatically handles the line wrap to the second line, or a new line character (\n) forces text to the second line.

Listing 2

Simulated Pi LCD Keypad

 

Figure 4: Simulated Raspberry Pi LCD keypad.

A common function, myfunc (line 4), is called when a button is pushed. In this example, the buttons pass their button text to myfunc, which then shows the custom text message in the two-line display.

NeoPixels

NeoPixels [5] are addressable full-color RGB LEDs that come in a variety of arrangements, such as LED strings (Figure 5), matrix arrays, Pi plates, and a variety of sewable components that can be used on wearable products. NeoPixels were first available only for Arduino projects, but now, Python libraries for Raspberry Pis are available, as well.

Figure 5: Some NeoPixel hardware.

Listing 3 is a Python Tkinter example that simulates 10 NeoPixels in a string arrangement (Figure 6). The array object ledstrip (line 10) becomes a number of colored Tkinter labels (line 13), which are placed sequentially in a grid to form a string (line 14). However, you could also arrange the labels into a matrix or a circle. An LED color is set with the configure(background= 'red') command (line 17).

Listing 3

Simulated NeoPixels

 

Figure 6: Simulated (bottom) and real (middle) NeoPixels.

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