This project is intended as a countdown timer for a UV exposure box for PCB development that uses fluorescent UV lamps (it will also work with any other lamp, don’t worry). It is based around a PIC16F627 micro and has following features:
- adjustable time in 15-second increments (up to 10 minutes)
- lamp preheat feature
- two button operation (with audible feedback)
- countdown alarm (when timer reaches zero)
- relay for lamp switching
- 7-segment display
10 minutes?
I have chosen the upper time limit of 10 minutes which should be more than enough for most applications and initial time is set for a 5 minute countdown (I’m preparing a revised software which will load initial time from EEPROM so it can be configured manually). Step increment of 15 seconds has been chosen partially due to ease of operation because there are only two buttons – time adjustment and start/stop. Time adjustment is incremental meaning that each time you press the button time is incremented by 15 seconds. When upper limit is reached time is reset to zero and the process repeats. Start/stop button is used for, you will never guess, starting and stopping the timer with lamp preheat feature.
