Going for Gold

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.

Author : Joseph Kopff - Copyright : Elektor