LIGHT-ACTUATED RELAY MODULE, 12 VDC

Relay board uses LM393 comparator.

Using this relay module as a false start trigger for the race starting lights I have been building using 1 watt LED lights. The ST-1172 laser module is a perfect light source and runs on 3 1.5V batteries. The CTM-70 cardboard tubes fit the CdS cell perfectly to eliminate stray light sources. Since this relay operates on 12VDC, it allows the entire system to run on battery power so we can set up anywhere. Added a LED-1 with a 680 ohm resistor between the Vcc and the NO terminal to aid in alignment of the unit. Could have used the blue LED but it was not bright enough. The starting lights are connected across the NC terminal and COM ground, so they trip the stop light if anyone starts early and breaks the laser beam.