Pi Sensor Python Example

For the final project, I want to show Raspberry Pi sensor data in a Whiptail message box. My setup uses a low-cost DHT11 temperature and humidity sensor (about $3-$10), but the more accurate DHT22 module could also be used. These sensors have a three-pin configuration with power, ground, and signal connections.

The Python library for both the DHT11 and DHT22 sensors is installed by:

pip install Adafruit-DHT

A Python wrapper library offers all the Bash Whiptail functionality. Note that this library requires that the basic Whiptail utility be installed as a prerequisite. To install the Python library, enter:

pip install whiptail-dialogs

Once the DHT and Whiptail libraries are loaded, you can create some lightweight projects that connect the sensor data with text interfaces.

The example in Listing 3 imports the Adafruit_DHT and Whiptail libraries (lines 5 and 6) and then reads the DHT11 sensor on pin 4 (line 9). The humidity and temperature values are put into a message string (line 12) that is shown in a Whiptail message box (line 15).

An alternative approach to the Python Whiptail library is to write all the code in a Bash script and then call Python in command-line mode. The Python command-line option -c executes a string of Python statements; for example:

$ python3 -c "a=4;b=5;print(f'{a}+{b}={a+b}')"
4+5=9

The Bash script in Listing 4 calls Python to return the sensor data as a Bash variable (msg; lines 8-15). Python imports the DHT library (line 11), reads the sensor (line 12), and then prints the results as a string (line 13). The Bash variable (msg) is then shown in a Whiptail message box (line 18).

Bash and Python scripts each have their own benefits and drawbacks, but the end result produces the same text interface. Figure 5 shows the Raspberry Pi hardware and the sensor data in a Whiptail message box interface.

Figure 5: Raspberry Pi sensor project.

Summary

Whiptail, preinstalled on Raspbian, is a simple tool for creating text-based interfaces. If you need more functionality, take a look at the Dialog [3] utility, which supports all the Whiptail features and about a dozen more presentation boxes. Two of the features I especially liked about Dialog are inline custom colors and the ability to refresh pages with a time-out parameter.