The title refers to a popular TV game show where the contestants each have a big button. The game show host asks a question and the first contestant to press their but-ton makes an illuminated indicator light up on their desk. The other contestants’ buttons are automatically inhibited, so that everyone can see who was the first contestant to press their button, and so is allowed to answer the question. The project described here shows how to build a similar sortof refereeing device yourself, using simple resources and without needing a microcontroller, which is pretty rare these days! The basic circuit is for just two contestants, but the modular design means it can easily be expanded.
Circuit diagram :
Going for Gold Circuit Diagram
The diagram shows three buttons: S2 and S3 are the buttons for the two contestants, S1 is the button for the host, which allows them to reset the circuit before each fresh question. The ‘brains’ of the circuit is IC1, a 4013 dual D-type flip-flop, of which only the Set and Reset inputs are used here. This circuit can handle quite a wide supply voltage range, from 3 to 15 V, and so the project can easily be run off a 4.5 V battery pack (the power consumption is minimal).
IC1 is armed by pressing S1 (reset). In this state, the non-inverting outputs (pins 1 and 13) are at 0 and the inverting outputs (pins 12 and 12) are at 1. Hence line A is pulled high by R1, since diodes D2 and D4 are not biased on. If contestant 1 presses button S2, the non-inverting output of flip-flop IC1a goes to logic 1, and LED D1 lights via T1 to indicate that contestant 1 has pressed the but-ton. At the same time, the flip-flop’s invert-ing output goes to logic 0, making diode D2 conduct. Line A is now pulled down to 0, and consequently contestant 2’s button S3 can no longer trigger the second flip-flop. The reverse happens if it is contestant 2 who presses their button S3 first.
The circuit can be extended to 4 or 6 contest-ants (or even more) by adding a second or third (or more) 4013 IC. All you have to do is repeat the circuit (minus R1, R2, and S1) and connect to the A, B, Vdd, and 0 V lines on the right-hand side.
