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A game show buzzer that knows who pressed first

Two players, two buttons: whoever presses first lights their LED and locks the other out. One flip-flop chip, no code.

Component side layout of A game show buzzer that knows who pressed first on a perfboard 16 by 30 holes — 16 × 30 holes · 13 parts · 25 wiresOpen the build sheet

Free build sheet

The parts, every wire with its length and bend points, a bend guide, both sides of the board and checkboxes to track your progress. Print it or keep it open at the bench.

Open the build sheet

What you need

13 parts on a perfboard 16 × 30 holes, plus hookup wire.

Qty	Part	Where to buy
1	Ceramic Cap100nF C1	Buy Ceramic Cap on Amazon
1	Power Input (2-pin) J1
1	LEDred LED1	Buy LED on Amazon
1	LEDblue LED2	Buy LED on Amazon
2	Resistor (axial)2.2k R1, R2	Buy Resistor (axial) on Amazon
3	Resistor (axial)4.7k R3, R4, R5	Buy Resistor (axial) on Amazon
1	DIP-14 U1
3	Tactile Button 6mm U2, U3, U4

Check every pin against the datasheet of the exact part in your hands before wiring.

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Cut list

25 wires, 791 mm (31.1 in) in total, in the order the build sheet cuts them. Wire numbers match the build sheet. Each length includes 5 mm per end to go through the hole.

Wire	Colour and net	Route	Length	Bends
24	BlackGND E4 → F5	E4 → F5	14mm	Straight
6	BlackBLUE_BTN J22 → J19	J22 → J19	18mm	Straight
18	Black9V C3 → G3	C3 → G3	20mm	Straight
12	BlackRESET M23 → I17	M23 → I17	29mm	10mm (45°)
23	BlueGND C10 → D5	C10 → D5	25mm	8mm (90°)
11	BlueRESET H27 → L24	H27 → L24	28mm	13mm (90°)
5	BlueLOCK_BLUE F13 → J17	F13 → J17	40mm	20mm (90°), 30mm (90°)
17	Blue9V E17 → B4	E17 → B4	51mm	13mm (90°)
4	GreenRED_LED D11 → D8	D11 → D8	18mm	Straight
16	Green9V B20 → G24	B20 → G24	33mm	15mm (90°)
10	GreenBLUE_Q M7 → F17	M7 → F17	53mm	30mm (90°)
22	GreenGND G23 → D9	G23 → D9	53mm	13mm (90°)
7	RedBLUE_BTN I18 → H17	I18 → H17	14mm	Straight
1	RedRED_Q D7 → D14	D7 → D14	28mm	Straight
19	RedGND L28 → J23	L28 → J23	28mm	18mm (90°)
25	RedGND B9 → N10	B9 → N10	43mm	8mm (90°)
13	RedRESET F27 → H13	F27 → H13	71mm	15mm (90°), 51mm (90°)
21	WhiteGND L16 → L14	L16 → L14	15mm	Straight
3	WhiteBLUE_LED M11 → M8	M11 → M8	18mm	Straight
15	White9V C21 → K21	C21 → K21	30mm	Straight
9	WhiteRED_BTN H18 → G13	H18 → G13	46mm	18mm (90°), 30mm (90°)
14	Yellow9V D20 → D16	D20 → D16	20mm	Straight
8	YellowRED_BTN D22 → G19	D22 → G19	25mm	13mm (90°)
20	YellowGND I24 → K17	I24 → K17	31mm	8mm (90°), 23mm (45°)
2	YellowLOCK_RED G17 → I13	G17 → I13	40mm	13mm (90°), 23mm (90°)

About this build

A two player game show buzzer with a first press lockout, and no code. Each player's button clocks one half of a CD4013B dual flip-flop.

The lockout is the neat part. Each flip-flop's data input listens to the other side's inverted output. The first press latches its own LED on, which drops the other side's data input low, so the second press only clocks in a zero. A third button resets both for the next round. Land both presses within about a tenth of a microsecond and both LEDs light, a tie no thumbs will manage.

The red and blue LEDs run straight off the chip outputs through 2.2k resistors, and 4.7k pull-downs keep every button input at a defined level when nobody's pressing. It runs on 9V and fits a 16 by 30 perfboard, power at the top and buttons at the bottom.

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Open the build sheet