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
Hi friend
Nice and simple circuit, the “SECOND”…
i would like to make it…
But i cannot the numbering connection of IC 7420 to others?
greetings ヅ
Thanks friend, I have updated the pinout details of the IC 7420 at the end of the post, you can connect them accordingly.
HI
Hi friend
Could this combinations below be correct?
(7420) 1-2-4 to 8 (7420)
(7420) 5 to (reset button)
(7420) 6 to 13-4 (7475)
(7420) 9 to 9 (7475)
(7420) 10 to 10 (7475)
(7420) 12 to 15 (7475)
(7420) 13 to 16 (7475)
Great thanks ヅ
Yes that looks OK to me.
could you modify this design to work with sound as an activator not a push button, im looking to create a “who fired first” for quick draw shooting so need a system that will pick up the bang of the first gun to fire and light its light disabling the opponents light, then auto reset after say 15sec.
Yes that may be possible. You will need 4 separate sound activated relay circuits, and then integrate the relay contacts with the relevant push switch contacts.
You can try the following sound activated relay circuit as an example:
https://www.homemade-circuits.com/wp-content/uploads/2022/04/clap-switch-staircase-lamp.jpg
Please ignore the LED bulb and its associated wiring.