This is good looking and practical device that may be useful in many areas where count down timer is needed (no bombs please). Its time can be adjusted in range from 1 minute to 99 minutes. It displays time sequence on BCD decoded 7 segment LED display. When count down finishes – timer sends a control signal to relay.
Complete design is made on wiring technique, so no PCB is available. Project is very well described with circuit operation animations what is really helpful for circuit beginners. Source code is also documented well with flow charts. Assembly code and hex file may be downloaded here.