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Make this Fastest Finger First Indicator Game Circuit

Make this Fastest Finger First Indicator Game Circuit

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.

Circuit Operation

Four press 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.



About the Author

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!

22 thoughts on “Make this Fastest Finger First Indicator Game Circuit”

  1. I had read data sheet of both ics but still i am getting those two mentioned problems in my circuit.
    What should i do, sir ?

    • sorry but just reading will not help you must try to understand how it is supposed to work

      7475 is a bistable latch…so may be due to switch ON surge all the bistables are latching together. the 0.22uF is actually placed to eliminate this switch ON surge…you can try shorting this capacitor manually to shut off the LEDs, if that doesn't help then your IC may be faulty or some other hidden fault might be there…actually pressing the reset MUST also reset the 7475, as this is supposd to cause a low logic at the output of 7420 bottom gate…you can attach an LED across the 7420 bottom gate output and ground to check how the reset button is responding.

  2. Sir,
    Here all leds are glowing but as per your principle the push button which will be press first, only that led which is corresponding to its particular push button will glow is unfortunately not occuring in my case.
    And reset button is not working.
    I need your help, please give me some solution.

    • Kaustubh, this circuit was referred from some other site…to troubleshoot the fault you will have to understand the logical behavior of the ICs. you can take the help of the datasheet of the specific ICs to view their internal gate configuration and then compare it with my article explanation, this might help you to figure out why your LEDs are always ON.

    • you'll have to study the functioning the IC pinouts and then troubleshoot yourself…It would be difficult for me to suggest without practically checking your assembly

  3. The led which is connected to the pin 15 and 16 of ic 7475 glows immediately when the power source is given….
    if the 4 th switch is pressed , the led connected to pin 9 glows….
    if the 3rd switch is pressed , the led connected to pin 10 glows…..
    but if either 1st or 2nd switch is pressed the led connected to pin 15 and 16 which is aldready glowing , glows brigther than the normal……..
    And the reset button is of no use or not working……
    pins 1,4,8,11 of ic 7475 is not used in the circuit , but in the data sheet these pins are mentioned as complementary input and output and enable . what about this ….whether it is related to this project…please give the solution for these problems as soon as possible………..

    its urgent , because the project must be submitted on thursday (28/08/2014)

    • I have modified the circuit a bit by adding a capacitor with pin 13/14 of the IC 7475..this is done to stabilize the circuit during power ON. Please do it accordingly.

      If still the problem persists could possibly mean a fault in your circuit connections or in the IC….remember the ICs work only with 5V.

    • mani, yes it's not clearly given in the schematic, please search for the datasheets of the ICs, from there you can easily find the required info.

  4. The above circuit is absolutely correct now…check all your connections again, check IC polarity, check grounds connections etc….

  5. The circuit is correct now according to the datasheet,

    remove the lower IC and confirm the upper IC functioning first.

    Initially all the 4 outputs will show high voltage (=5V), as soon as one of the switches is pressed the relevant output will become low (0V) and the particular LED will light up.

  6. how much voltage did you use as the supply…remember it should not exceed 5V, if it exceeds even by 1v, the ICs will gets damaged.

  7. Let's go step wise.

    Initialy remove the 7420 IC, and short the reset switch pins, and check the outputs by pressing the buttons, the LEDs should light up and stay latched.

    Please confirm this first then we'll proceed with the remaining functions.

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