A timer uses counter which counts at certain speed depending upon the clock frequency. In Arduino Uno it takes 1/16000000 seconds or 62nano seconds ... using pushbuttons. Complete code for Arduino ...

The idea is fairly simple as it mainly requires a TM1637 4-digit display and a Digispark USB development board. Fig. 1: Digispark board TM1637 ... shows live status of the countdown timer.

Electronics designer Patrick Thomas Mitchell has returned once again to Kickstarter to launch his new Raspberry Pi and Arduino programmable timer ... circuit board is production ready, the version ...