• Skip to main content
  • Skip to primary sidebar

Homemade Circuit Projects

Get free circuit help 24/7

New Projects | Privacy Policy | About us | Contact | Disclaimer | Copyright | Videos | Circuits for Beginners | Basic Circuits | Hobby Projects | Transistor Circuits | LED Drivers 

You are here: Home / Fun Projects / 2 Simple Fastest Finger First Circuits Explained

2 Simple Fastest Finger First Circuits Explained

Last Updated on January 29, 2023 by Swagatam 10 Comments

caution electricity can be dangerous

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

8 Contestant Fastest Finger First Circuit Using IC 555

The main function of our next fastest finger first circuit is to reveal which of the potential eight participants dialed in first, so that person can respond to a question. The competitors receive an auditory signal from it to tell them to halt trying to ring in.

The circuit moves quickly, almost eliminating the possibility of a deadlock between two or more competitors.

The eight silicon-controlled rectifiers in the circuit conduct when switches S1 through S8 are closed, activating relay K1.

This then disables power to the switches and activates the audio oscillator/timer portion, making it difficult for anybody else to call in. The voltage drop across the equivalent 100 ohm resistor causes the competitor's LED to turn on.

The audio oscillator, which generates a high pitched sound, is made up of the timers U2 and U3. Potentiometers R1 and R2 can be adjusted to change their frequency.

The 4017 decade counter/divider, U5, and the 555 timer U4 make up the timer part. By varying the potentiometer R3 causes the 555 IC to produce the timing pulses which is fully adjustable.

The transistor Q1 switches on and K2 is activated once pin 9 of the 4017's timer sequence achieves a high state. This resets the circuit.

3 Competitor Fastest Finger Response Monitor Circuit

Our final circuit creates a simpler, three-competitor fastest finger first monitor circuit by combining NAND gates and SCRs.

In this circuit, we use a 4081 quad 2-input AND gate, which controls the logic between the SCRs.

Remember that if any input of an AND gate is low, the output will likewise be low; hence, an AND gate cannot have a high output if any of its inputs is low.

When the circuit is reset (through S4), the three SCRs are turned off, each AND-gate input is high, and the outputs of the AND gates are also high.

The three gates' outputs are high enough to provide the gate current required to switch on each SCR. If S1 shuts first, SCR1's gate is activated and LED1 is lit by the high output of U1a applied through R1 to the gate.

The inputs of U1b and U1c, which are connected to the anode of SCR1 at pins 6 and 9, respectively, are pushed low at the exact same time. Because of this, SCR2 and SCR3 have low output and cannot be switched on.

You'll also like:

  • 1.  Electromagnetic Levitation Circuit [Anti-gravity]
  • 2.  Make this Simple Weather Station Project for Homes and Offices
  • 3.  Simplest Quadcopter Drone Circuit
  • 4.  4 Easy Boost Converter Circuits Explained
  • 5.  Blinking LED Circuit using LDR and Resistors
  • 6.  4 Simple Power Bank Circuits for Mobile Phones

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!

Reader Interactions

Comments

    Have Questions? Please post your comments below for quick replies! Comments should be related to the above artcile Cancel reply

    Your email address will not be published. Required fields are marked *

  1. Ramesh Lalla says

    September 18, 2022

    hi Sawgatam, can you please help me with a circuit design, whereby a switch is at each bed side patient, to alert the nurse for assistance, total of 8 patients, one switch per patient each in different rooms. the nurse in a separate “control room”. so a small buzzer and a led light to identify the patient who requires help.

    Reply
    • Swagatam says

      September 18, 2022

      Hi Ramesh,
      I think have a related post available in this blog, you can checkout the following post:

      https://www.homemade-circuits.com/hospital-room-call-bell-circuit/

      Reply
      • Ramesh Lalla says

        September 18, 2022

        hi Swagatam, thank you so very much for your speedy response, i will check out the circuits

        Reply
        • Swagatam says

          September 19, 2022

          Thanks Ramesh, I am glad to help!

          Reply
  2. Yedan says

    April 22, 2022

    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.

    Reply
    • Swagatam says

      April 23, 2022

      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.

      Reply
  3. Hid Per says

    February 29, 2020

    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

    Reply
    • Swagatam says

      February 29, 2020

      Yes that looks OK to me.

      Reply
  4. Hid Per says

    February 28, 2020

    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

    Reply
    • Swagatam says

      February 29, 2020

      Thanks friend, I have updated the pinout details of the IC 7420 at the end of the post, you can connect them accordingly.

      Reply

Primary Sidebar

Calculators

  • 3-Phase Power (15)
  • 324 IC Circuits (19)
  • 4017 IC Circuits (52)
  • 4060 IC Circuits (25)
  • 555 IC Circuits (98)
  • 741 IC Circuits (19)
  • Arduino Engineering Projects (83)
  • Audio and Amplifier Projects (114)
  • Battery Chargers (82)
  • Car and Motorcycle (94)
  • Datasheets (46)
  • Decorative Lighting (Diwali, Christmas) (33)
  • Electronic Components (100)
  • Electronic Devices and Circuit Theory (36)
  • Electronics Tutorial (116)
  • Fish Aquarium (5)
  • Free Energy (34)
  • Fun Projects (13)
  • GSM Projects (9)
  • Health Related (20)
  • Heater Controllers (29)
  • Home Electrical Circuits (102)
  • How to Articles (20)
  • Incubator Related (6)
  • Industrial Electronics (28)
  • Infrared (IR) (40)
  • Inverter Circuits (98)
  • Laser Projects (12)
  • LED and Light Effect (93)
  • LM317/LM338 (21)
  • LM3915 IC (25)
  • Meters and Testers (65)
  • Mini Projects (148)
  • Motor Controller (67)
  • MPPT (7)
  • Oscillator Circuits (26)
  • PIR (Passive Infrared) (8)
  • Power Electronics (34)
  • Power Supply Circuits (77)
  • Radio Circuits (10)
  • Remote Control (48)
  • Security and Alarm (61)
  • Sensors and Detectors (120)
  • SG3525 IC (5)
  • Simple Circuits (75)
  • SMPS (29)
  • Solar Controllers (60)
  • Timer and Delay Relay (53)
  • TL494 IC (5)
  • Transformerless Power Supply (8)
  • Transmitter Circuits (40)
  • Ultrasonic Projects (16)
  • Water Level Controller (45)

Calculators

  • AWG to Millimeter Converter
  • Battery Back up Time Calculator
  • Capacitance Reactance Calculator
  • IC 555 Astable Calculator
  • IC 555 Monostable Calculator
  • Inductance Calculator
  • LC Resonance Calculator
  • LM317, LM338, LM396 Calculator
  • Ohm’s Law Calculator
  • Phase Angle Phase Shift Calculator
  • Power Factor (PF) Calculator
  • Reactance Calculator
  • Small Signal Transistor(BJT) and Diode Quick Datasheet
  • Transistor Astable Calculator
  • Transistor base Resistor Calculator
  • Voltage Divider Calculator
  • Wire Current Calculator
  • Zener Diode Calculator

© 2023 · Swagatam Innovations