2 Simple Fastest Finger First Circuits Explained

The 2 simple fastest finger first indicator circuits presented here can be used for indicating which candidate was the first to press the answer button out of the 4 participating candidates in a quiz contest.

We all have probably seen the famous game show "who wants to be a millionaire" and many similar quiz shows, where in the initial stages a few of the participants are asked to go through a small test, the participants are asked a question, and the member who answers it first by pressing the buzzer is given the opportunity to occupy the "hot seat".

Well everybody might not be as lucky to get into such game shows, but you can certainly enjoy making and playing with this little fastest finger first decider circuit right in your home.The circuit is very simple, utilizes just a couple of ICs and some LEDs.

Design #1 using IC 74122

In a 'professional' quiz game set up, we may require some form of electronic detector for accurately detecting the fastest candidate pressing the buzzer button and the first candidate to answer an asked question.

The simple fastest finger first circuit using IC 74122 shown below is designed to implement the proposed task.

Circuit Description

Push-button S5 is one button that is controlled by the quiz master.

As long as the quiz master keeps this button depressed, all the LED indicator stages remain disabled. The moment he releases S5 all the remaining circuits and the associated press buttons become active.

The candidate who presses one of the assigned buttons (S1-S4), it triggers the monostable (IC1 -IC4) stage connected with that button.

The monostable switches ON the respective indicator LED and at the same time blocks the other three monostables by means of N1.

The period for which the monostables remain disabled is around 8 seconds, after this delay the indicator lamp switches OFF allowing the other candidates to resume the fastest finger first game. The quiz master has the power to reset all monostables whenever he wants it, or when it is essential to 'override' button S5.

Design #2 Using IC 7475

In the second design four push-to-ON type of switches are placed at the input of the IC 7475 which is a 4-Bit Bistable Latch with Complementary Outputs.

The button which is pressed first, triggers the relevant output of the IC 7475, which in turn prompts the IC 7420 to instantly deactivate the other inputs from the other push buttons, rendering the whole system inactive, except the one which had the first trigger through the push button.

This output concerning the triggered latch illuminates the relevant LED, indicating the button number which was pressed first.

The is a simple game circuit which can be built by all electronic hobbyists and also school kids.

Pinout Details of IC 7420

About Swagatam

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials.
If you have any circuit related query, you may interact through comments, I'll be most happy to help!