The presented digital timer is built in addition to the before mentioned ultraviolet light box.
Indication is on 4 digits seven segment LED display.
The timer counting backwards from 99 minutes and 59 seconds to 00:00.
It is built with microcontroller PIC 16F84A and integrated circuit CD4511.
Supply for the ultraviolet LED diodes are terminated with the help of the electromagnetic relay 6Volti.
Set the countdown time is done with 2 command keys, and the timer starts with the tally.
Source: Magazine Emiter