BBC micro:bit Counter using a 7-Segment Display

The aim of this challenge is to create a countdown timer, controlled by a BBC micro:bit that will display the numbers on a screen using a 7-segment display. A lot of electronic devices use this approach to display numbers on a LED or LCD screen. (Watch, alarm clock, calculator etc.)

Typically 7-segment displays consist of seven individual coloured LED’s (called the segments). Each segment can be turned on or off to create a unique pattern/combination. Each segment is identified using a letter between A to G as follows:

The following truth table shows which segments need to be on to display the digits from 0 to 9:

Digit	A	B	C	D	E	F	G
	1	1	1	1	1	1	0
	0	1	1	0	0	0	0
	1	1	0	1	1	0	1
	1	1	1	1	0	0	1
	0	1	1	0	0	1	1
	1	0	1	1	0	1	1
	1	0	1	1	1	1	1
	1	1	1	0	0	0	0
	1	1	1	1	1	1	1
	1	1	1	1	0	1	1

Step 1: The electronic circuit

• 1 breadboard
• 8 resistors of 220Ω each
• 1 7-segment display (common anode)
• 1 BBC micro:bit
• 1 micro:bit edge connector
• 20 wires

Here is the circuit that you will need to re-create:

Step 2: Python Code

To program your BBC micro:bit you will use the Python editor and copy and paste the following code:

#micro-bit Counter using a 7-Segment Display - www.101computing.net
from microbit import *

pins = [pin0, pin1, pin2, pin8, pin12, pin13, pin14, pin15]
digits = ["11111100","01100000","11011010","11110010","01100110",
          "10110110","10111110","11100000","11111110","11110110"]

while True:
    for i in range(0,10):
        bits=digits[i]
        for j in range(0,8):
            pins[j].write_digital(int(bits[j]))
        display.scroll(str(i))
        sleep(1000)

Your 7-segment display should display all the digits, counting up from 0 to 9.

Your Challenge

• Create a count down timer, going from 9 to 0.
• Allow the user to pause and restart the countdown timer using the A and B buttons of the micro:bit.