Ultraviolet PCB exposure has to be performed very exactly. Quality may differ even if you under expose or over expose lets say 5 or 10 seconds. So it is better to rely counting to hardware timer that human. This dark room timer has all features needed to control any PCB exposure box or other devices if needed. Practically it is universal timer which can control lamps, heaters etc. because it uses a switching relay.

Current time is displayed by 4 seven segment LED indicators mounted on separate PCB. Also there is a bicolor led used for timer status indication - standby and counting. All project files including circuits, PCB and asm source code can be downloaded here. [link]

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