How to control a 7 Segment Display from Raspberry PI with Python
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7 segment display is a simple electronic display composed of 7 (surprise) LEDs. It is common to find an addictional led for a little dot near classic 7 segments.
It is used within a wide number application, usually to diplay numbers.
These devices have a simple internal wiring diagrams, which maps one by one LEDs to its pins:
In this article we’ll control a 7 Segment Display from a Raspberry PI Zero W. This article applies also to newer Raspberry PI boards.
What We Need
As usual, I suggest adding from now to your favourite ecommerce shopping chart all needed hardware, so that at the end you will be able to evaluate overall costs and decide if continuing with the project or removing them from shopping chart. So, hardware will be only:
- Raspberry PI Zero W (including proper power supply or using a smartphone micro usb charger with at least 3A)
- micro SD card (at least 16 GB, at least class 10)
- a 7 Segment Display
- Breadboard
- Dupont wirings
- 8x resistors (220 Ohm used)
Many of listed hardware (except from Raspberry PI Zero W and micro SD Card) can be bought alone or can be also found in the useful Elegoo starter kit.
Step-by-Step Procedure
Wiring Diagram
Prepare cabling according to following wiring diagram:
This wiring produces the following mapping between Display and Raspberry PI:
| Display Segment | Display Pin | Raspberry PI phisical pin | Raspberry PI BCM GPIO |
| A | 7 | 11 | 17 |
| B | 6 | 13 | 27 |
| C | 4 | 15 | 22 |
| D | 2 | 19 | 10 |
| E | 1 | 21 | 9 |
| F | 9 | 23 | 11 |
| G | 10 | 29 | 5 |
| DP | 5 | 31 | 6 |
| GRD | 3 | 6 | GRD |
| GRD | 8 | 6 | GRD |
So, each Raspberry PI pin / GPIO powers on/off its related segment. Powering on appropriated segments together will display the number we want to show.
Please find below the overall picture:
OS Preparation
Start with OS installation using Install Raspbian Buster Lite guide.
Make your OS up-to-date:
sudo apt update sudo apt upgrade
Python Scripting
Install GPIO
sudo apt install rpi.gpio
Get from my download area segDisplay.py script:
wget https://peppe8o.com/download/python/segDisplay.py
Script Usage
This script can be used by simply calling segDisplay.py with a simple argument passing the number to display and the dot (if required). So, for example:
python3 segDisplay.py 1.
Will display the number “1” and powers ON the dot led.
python3 segDisplay.py 5
Will display the number “5” and powers OFF the dot led.
python3 segDisplay.py 10
Will power OFF the whole display.
Script explaination
First section imports required libraries
import sys
import RPi.GPIO as GPIO
This script works mapping following pins activation according to wiring diagram:
Num_to Display -> GPIO pins state 0 -> [1,1,1,1,1,1,0] 1 -> [0,1,1,0,0,0,0] 2 -> [1,1,0,1,1,0,1] 3 -> [1,1,1,1,0,0,1] 4 -> [0,1,1,0,0,1,1] 5 -> [1,0,1,1,0,1,1] 6 -> [1,0,1,1,1,1,1] 7 -> [1,1,1,0,0,0,0] 8 -> [1,1,1,1,1,1,1] 9 -> [1,1,1,1,0,1,1] 10 (OFF) -> [0,0,0,0,0,0,0]
Dot GPIO (6) is managed alone. Last array is used to deactivate the Display.
GPIO id order is stored in a simple array. GPIO order is according to mapping. GPIO are also all set as output.
display_list = [17,27,22,10,9,11,5] GPIO.setmode(GPIO.BCM) GPIO.setwarnings(False) for pin in display_list: GPIO.setup(pin,GPIO.OUT) # setting pins GPIO.setup(6,GPIO.OUT) # setting dot pin GPIO.setwarnings(True)
Warnings are disabled because this script will leave display active after execution.
A new array is defined, listing all possible combinations to Display. So, arrSeq[0] stores GPIO status to show “0” on display. arrSeq[10] will be managed alone to push a GPIO.cleanup.
arrSeg = [[1,1,1,1,1,1,0],\ # -> arrSeq[0] displays 0 [0,1,1,0,0,0,0],\ # -> arrSeq[1] displays 1 [1,1,0,1,1,0,1],\ # -> arrSeq[2] displays 2 [1,1,1,1,0,0,1],\ # -> arrSeq[3] displays 3 [0,1,1,0,0,1,1],\ # -> arrSeq[4] displays 4 [1,0,1,1,0,1,1],\ # -> arrSeq[5] displays 5 [1,0,1,1,1,1,1],\ # -> arrSeq[6] displays 6 [1,1,1,0,0,0,0],\ # -> arrSeq[7] displays 7 [1,1,1,1,1,1,1],\ # -> arrSeq[8] displays 8 [1,1,1,1,0,1,1]] # -> arrSeq[9] displays 9
Then a basic error check on passed argument is performed. On error, program exits:
if len(sys.argv) > 2:
print("ERROR: too many arguments")
sys.exit()
elif len(sys.argv) == 1:
print("ERROR: missing argument")
sys.exit()
elif int(sys.argv[1].replace(".", "")) > 10 or int(sys.argv[1].replace(".", ""))<0:
print("ERROR: insert a number between 0 and 10")
sys.exit()
Dot led activation is managed alone, so only number is passed to main diplay procedure:
if sys.argv[1].count(".") == 1:GPIO.output(6,1)
numDisplay = int(sys.argv[1].replace(".", ""))
FInal operation is just activating GPIOs according to number passed on argument. This script then exits:
if numDisplay == 10: GPIO.cleanup() else: GPIO.output(display_list, arrSeg[numDisplay]) sys.exit()
Enjoy!