Programming with Python Turtle graphics
Turtles
Create a bulb and tube analog thermometer with a Raspberry Pi and Python Turtle graphics.
Turtle graphics are a great way to get kids started programming. The Python turtle library offers simple step-by-step graphical methods that allow young programmers to create graphics with only a few lines of code.
I found that once my kids understood Turtle basics, we were able to do more advanced Raspberry Pi projects that used sensors, push buttons, and outputs. In this article, I share a Rasp Pi Turtle project that creates a graphic of an "old style" mercury thermometer animated with a Pi temperature sensor.
Getting Started
The Python turtle library is probably already loaded on your Raspberry Pi system, but if it is not, enter:
pip install turtles
The turtle library [1] is used a little bit as you would use a pen on a drawing board. With the use of methods (e.g., forward()
, backward()
, left()
, and right()
), you can draw lines. If you want to move a turtle without drawing a line, you use the penup()
method; then, once you arrive at the desired location, the pendown()
method lets you start drawing again. Turtle objects have properties for color and line thickness and a number of additional methods for shapes, fill, circles, and text.
To create a turtle object, you use the myturtle = Turtle()
statement. A new turtle is placed at the center of the screen, position (0,0), facing right.
The Python Turtle example in Listing 1 shows three basic concepts I use in this project: drawing lines, moving without drawing, and adding text (Figure 1).
Listing 1
turtle1.py
To draw t1
, named turtle
(line 7), the turtle (pen) rotates 90 degrees left to face toward the top of the drawing area (line 9). With a combination of left
and forward
methods, turtle t1
becomes an open rectangle (lines 9-14).
The t2
shape is red and drawn with a thick pen size (lines 18-20). The up()
method makes sure the pen does not draw while it moves (line 21-22). After reaching the new position, the pen goes back down to draw a circle (lines 23-24). The pen for turtle t3
goes to a new position without drawing a line and writes some text on the screen (line 27-31).
Once you (or your young programmer) have mastered drawing lines, moving without drawing, and adding text, you can start some more interesting projects.
Drawing a Thermometer
For this project, I wanted to draw an "old style" mercury thermometer with a bulb of red mercury at the bottom and a tube above it (Figure 2).
Simple turtle commands like move
, left
, right
, and forward
are great for drawing simple graphics, but they can be awkward if you want to create a more complex drawing. A more efficient approach is to define an array of (x, y) coordinates and move to each position in the array. For example, the upper tube can be drawn with:
# An array of coordinates for the tube outline = ((25,-50),(25,210),(-25,210),(-25,-50)) for pos in outline: # move to each tube x,y point t1.goto(pos)
To draw the lower "mercury" bulb in this project, I enhance the circle of my first example, turtle t2
, by creating a black circle with red fill. The fill is toggled with the begin_fill()
/end_fill()
methods:
# put the pen up and move to the circle starting point t2.penup() t2.goto(0,-137) t2.pendown() t2.pensize(5) t2.color("black","red") # draw the circle with fill t2.begin_fill() t2.circle(50) t2.end_fill()
At this point, I've created a static background for the thermometer. The next step is to read a temperature value from the Raspberry Pi and add dynamic information to the drawing.
Hardware Setup
A number of different temperature sensors can be used for this project. Here, I use a low-cost ($5) DHT11 temperature/humidity sensor [2]. This sensor has three pins, (signal, 5V, and GND; Figure 3). The signal pin connects to Rasp Pi physical pin 7 (PP7). The program in Listing 2 tests the DHT11 sensor. Note that because the sensor can return a humidity value, you could add that information in your Turtle code, as well (line 12).
Listing 2
test.py
To install the DHT temperature sensor Python library [3], enter:
sudo pip install Adafruit_DHT
When I'm doing Pi projects with my kids, I like to use prototyping expansion tops (Figure 4). These tops start at around $6 [4]. Not only do they make the wiring cleaner, it's a lot easier to move the projects around for testing.
Buy this article as PDF
(incl. VAT)
Buy Linux Magazine
Subscribe to our Linux Newsletters
Find Linux and Open Source Jobs
Subscribe to our ADMIN Newsletters
Support Our Work
Linux Magazine content is made possible with support from readers like you. Please consider contributing when you’ve found an article to be beneficial.
News
-
TUXEDO Computers Unveils Linux Laptop Featuring AMD Ryzen CPU
This latest release is the first laptop to include the new CPU from Ryzen and Linux preinstalled.
-
XZ Gets the All-Clear
The back door xz vulnerability has been officially reverted for Fedora 40 and versions 38 and 39 were never affected.
-
Canonical Collaborates with Qualcomm on New Venture
This new joint effort is geared toward bringing Ubuntu and Ubuntu Core to Qualcomm-powered devices.
-
Kodi 21.0 Open-Source Entertainment Hub Released
After a year of development, the award-winning Kodi cross-platform, media center software is now available with many new additions and improvements.
-
Linux Usage Increases in Two Key Areas
If market share is your thing, you'll be happy to know that Linux is on the rise in two areas that, if they keep climbing, could have serious meaning for Linux's future.
-
Vulnerability Discovered in xz Libraries
An urgent alert for Fedora 40 has been posted and users should pay attention.
-
Canonical Bumps LTS Support to 12 years
If you're worried that your Ubuntu LTS release won't be supported long enough to last, Canonical has a surprise for you in the form of 12 years of security coverage.
-
Fedora 40 Beta Released Soon
With the official release of Fedora 40 coming in April, it's almost time to download the beta and see what's new.
-
New Pentesting Distribution to Compete with Kali Linux
SnoopGod is now available for your testing needs
-
Juno Computers Launches Another Linux Laptop
If you're looking for a powerhouse laptop that runs Ubuntu, the Juno Computers Neptune 17 v6 should be on your radar.