it counts down from 20 and lights up pin 13 LED when the timer is complete.
It uses no extra hardware which is usefull for low-cost projects.
It also features multiplexing to get the job done with only 9 pins altogether for the displays.
Step 1: Parts needed
1. An Arduino (any kind will do)
2. A dual-7 segmant display or 2 seperate 7 segment displays.
3. 2 Resistors (the values depend on your display)
4. About 50cm of non-stranded wire
1. A soldering iron and solder. (My display was SMD so i had to solder wires to it for connection)
2. A fume extractor. (I really reccomend buying or making one as they are very helpful to you)
3. A wire stripper, or you could just use scissors