Easy circuit question

Thread Starter

FuneralHomeJanitor

Joined Oct 12, 2019
34
Hey everyone, this is probably a really simple circuit for most people on here but for some reason I have a mental block or my preventing me from coming up with it.

I am trying to build a device for playing games that has two push buttons and at least 2 LEDs that are controlled each by a button. I was trying to use one or two SR flip flops(still in the early stages of designing this, and my knowledge is limited).

I want the first button pushed to latch the circuit and keep ONLY the corresponding LED lit so we can see who rang in first.
How can I prevent the other LED from lighting after that button is pushed? I am not concerned about any other aspect of the circuit right now besides only allowing one LED to be lit and basically making the other push button useless after the first one is pushed.

I think I am significantly over complicating this. I have thought about everything from relays to capacitors to comparators and it is overwhelming and driving me crazy! Thanks in advance!
 

AnalogKid

Joined Aug 1, 2013
9,248
What you are after is called a game show circuit. Usually it is for 4 or more players, and that affects the circuit complexity. For only two players, things can be simplified. Still, you need a way to reset the system for another round. Disconnecting and reconnecting the power source gets tedious, so consider a third button for Reset.

A very simple version uses small SCR's as the latches (no logic devices). An ultra-simple version uses a neon light as the winner indicator, the latch, and the loser lockout, all in one (no active components of any kind).

https://images.search.yahoo.com/sea...nRpZAMEc2VjA3Nj?p=game+show+circuit+schematic

ak
 

bwilliams60

Joined Nov 18, 2012
1,398
Do you have any particular parts in mind in terms of pushbuttons, LEDs, a power supply of sorts or will this run on mains voltage? A little moremdetail and I am suremyou will get your answet. Is this something that people will hit hard with excitement or just a light touch. How robust do you want it to be? Do you need a reset, counters, do you want a microcontroller or a very basic circuit. Do you have access to parts where you are?
 

AnalogKid

Joined Aug 1, 2013
9,248
The classic approach needs two chips. One is a dual flipflop configured as a latch, and two quad AND gates to handle the inhibit logic. Also, assuming this is a low voltage DC circuit, each output will need a small MOSFET to drive the LED. 3 small capacitors, 3 resistors, and the switches. Does this sound like something within your assembly/test skill set?

ak
 
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Thread Starter

FuneralHomeJanitor

Joined Oct 12, 2019
34
What you are after is called a game show circuit. Usually it is for 4 or more players, and that affects the circuit complexity. For only two players, things can be simplified. Still, you need a way to reset the system for another round. Disconnecting and reconnecting the power source gets tedious, so consider a third button for Reset.

A very simple version uses small SCR's as the latches (no logic devices). An ultra-simple version uses a neon light as the winner indicator, the latch, and the loser lockout, all in one (no active components of any kind).

https://images.search.yahoo.com/sea...nRpZAMEc2VjA3Nj?p=game+show+circuit+schematic

ak
I was inspired by an circuit someone had made that used SCR/thyristors. I considered getting them, but haven’t used one although I am aware of what they are, and thought the SR flip flop circuit could be a good alternative. I was just trying to do 2 players, and I considered using two flip flops with the “resets” connected to each other so one button could reset both at the same time. I looked at some of the circuits but I think the “lockout” part is what I am trying to figure out. How can I achieve the “lockout?” Thanks for your response
 

SamR

Joined Mar 19, 2019
3,402
Pretty simple to breadboard @ 5V and using LEDs. Different colored LEDs for the various teams is one option. Go from there to soldered perfboard for a more permanent solution. Cabled switches as long as you need them for the number of teams/players and the local reset on the board or another cabled switch for you emcee/game master. Should be cheaper than SCRs/triacs and 12V lamps and power unless you want everyone in an auditorium to see it.
 

AnalogKid

Joined Aug 1, 2013
9,248
I was just trying to do 2 players, and I considered using two flip flops with the “resets” connected to each other so one button could reset both at the same time. I looked at some of the circuits but I think the “lockout” part is what I am trying to figure out. How can I achieve the “lockout?”
You cannot achieve lockout with only input connections. There has to be feedback from the latches so the lockout condition remains after the buttons are released. Through gating, the output of each flipflop locks out the other flipflop's input.

The CD4013 works well because it is an edge-triggered flipflop with an asynchronous reset input. That is, the Reset input takes precedence over the clock and data inputs instantly, not just at the next clock edge (that would be a synchronous reset). This makes it possible to reset the ff even if its clock signal has been locked out.

Thinking it through, this could be done with two S-R NAND-gate flipflops and two NAND gates for steering. So the latest BOM is two quad-NAND gates (4093, 4011), 3 resistors, and 3 caps.

ak
 
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