Good Afternoon,

i am currently undertaking a school project for my electronics course, i have constructed a game show buzzer circuit. (as shown in the image)

i completed the circuit up to the point where i only had to attach my 4072 and the buzzer. this is when i encountered a major problem. Before progressing further i found that the green LED would not be locked out by the 4013's when other LEDs where in operation. The circuit is meant to allow one led on at a time. The Green LED functions normally when it turned on first, not allowing any other LEDs to turn on. However it still turns on if its push button is pressed, even though another led could be turned on.

i have replaced every chip on this circuit and it does not seem to solve the problem.

Any help would be greatly appreciated,

thank you.

 

the D pins need to go to a gate that is held high, and not all tied to positve, connect them to the output of the quad And chip cd4082, pin 1,

this gate has a high on reset and goes low on receive of a clock sate.

 

If I understand you, it worked correctly before the addition of the 4072 and associated buzzer circuitry?

I have a thread in "Completed Projects" for this particular circuit.

I would have grounded the LEDs and taken the input to the 4072 OR gate directly from the 4013 Q outputs; in parallel with the LEDs. There may not be sufficient voltage as input to the OR gate, and the circuit may be left in an indeterminate state.

 

Remove the LEDs (and the resistors R6-R9).

 

the D pins need to go to a gate that is held high, and not all tied to positve, connect them to the output of the quad And chip cd4082, pin 1,

this gate has a high on reset and goes low on receive of a clock sate.

In this circuit, the D input can be tied high. See this project. It works fine.

 

no i have not yet connected my circuit to the extension including the 4072 and buzzer, but thank you for that great suggestion on how to add it.

if leaving my D pins tied to high is not a problem ( as you mentioned in your Project ) then what is causing this stubborn little LED to continue to not be locked out

 

The

Remove the LEDs (and the resistors R6-R9).

Then how will who buzzed in first be displayed?

 

I didn't examine the whole function of the project thoroughly. If you want LED indication of the status of the flip-flops you need to use LED drivers such as hex inverters connected to the output of the flip-flop. The LEDs as shown in the circuit schematic are in the wrong location.

 

I didn't examine the whole function of the project thoroughly. If you want LED indication of the status of the flip-flops you need to use LED drivers such as hex inverters connected to the output of the flip-flop. The LEDs as shown in the circuit schematic are in the wrong location.

what should the correct locations or format be then?
when tested on live wire the circuit functioned flawlessly

 

guys i have done all off the suggested ideas but none of them are working the circuit isn't working i need this urgent. forget the 4072 extension in need the four LEDs functioning 100% my deadline is next week

 

@MrChips has identified a fundamental flaw in the circuit. You can't have the LEDs hooked up like that because
1) you can't drive the inputs of the 4072 through a diode and expect logic levels and
2) you can't get enough current through the input of the 4072 to turn on the LEDs.
Relocate the cathode of the LEDs to ground and relocate the inputs of the 4072 to the outputs of the D flip flops. Make sure that the LEDs do not sink so much current as to drag down the logic output from the D flip flops. If they do, you'll need a buffer as suggested above.

I'd also put the buzzer in the collector of the transistor.

 

@MrChips has identified a fundamental flaw in the circuit. You can't have the LEDs hooked up like that because
1) you can't drive the inputs of the 4072 through a diode and expect logic levels and
2) you can't get enough current through the input of the 4072 to turn on the LEDs.
Relocate the cathode of the LEDs to ground and relocate the inputs of the 4072 to the outputs of the D flip flops. Make sure that the LEDs do not sink so much current as to drag down the logic output from the D flip flops. If they do, you'll need a buffer as suggested above.

I'd also put the buzzer in the collector of the transistor.

duly noted, what if i took out the 4072 and just grounded my LEDs is the schematics of my circuit correct? i designed them on live wire

 

what if i took out the 4072 and just grounded my LEDs is the schematics of my circuit correct?

Why? Are you out of wire? There's no reason why you can't use the 4072 if properly implemented. Assuming the buzzer is part of the spec, you'll have to deal with it eventually. What I posted makes the D outputs to the buzzer gate and LEDs parallel so that, assuming you don't overload the D outputs, it should work fine.

i designed them on live wire

I don't know what that is but if it signed off on this circuit - I would be highly suspicious of anything it told me.

I understand the time pressure but resist the temptation to start a lot of monkey-motion in hopes that you'll stumble on a solution. The way to approach these things is to put aside the time pressures and carefully analyze the problem, separate out things that work from those that don't etc. Its common to have something that works logically but fails when you hook it to the real world. Disconnect the LEDs and verify with a logic probe or DVM that the D outputs work and the output of the combining buzzer gate does as well. Then hook up the LEDs and if it works fine. If not, fix THAT part without flailing around in the logic. Make sense?

We used to have a little ditty that described how some guys approached problems:

When in trouble
When in doubt
Run in circles
Scream and shout

Entertaining but not really useful.

Good luck

 

Hi

Here's another way.

(ignore word "debouncer" over FF's. Each FF is configured as latch.)

eT