Game Show Indicator Lights Whos First
The circuit below turns on a light corresponding to the first of several buttons pressed in a "Who's First" game. Three stages are shown but the circuit can be extended to include any number of buttons and lamps. Game Show Indicator Lights Circuit Diagram: Three SCRs (silicon controlled rectifiers) are connected with a common cathode resistor (50 ohm) so that when any SCR conducts, the voltage on the cathodes will rise about 7 volts above the voltage at the junction of the 51K and 1K ohm resistors and prevent triggering of a second SCR. When all lamps are off, and a button is pressed, the corresponding SCR is triggered due to the voltage at the divider junction being higher than the cathode. Once triggered, the SCR will remain conducting until current is interrupted by the reset switch. Or, you can just turn the power off and back on. A 50 ohm, 5 watt resistor was selected to produce a 10 volt drop at 200 mA when a single 25 watt lamp comes on. Higher wattage lamps would ...