Countdown

The aim of this blog post is to create a countdown timer that will display the numbers on 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.)

First we need to investigate how the 7-segment display works. You will find this page quite useful.

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

Your Challenge

The code below is used to display a countdown timer counting from 5 to 0 and using the 7-segment approach to display the numbers.

Your challenge consists of using the truth table given in this post to start your countdown from 9 (instead of 5).

Challenge #2:

With 7 segments there are 128 possible symbols. Some can be used to represent letters. For instance:



Tweak the code above to write a message using the 7-segment display.

Start with the following message “Hello” (HELLO)