Stupidly simple circuit question - answered.

OK, so I accidentally volunteered to make an X-factor type buzzer board for a school event.

Three switches.  Throw each switch, in any order, a light comes on.

Throw the third switch, in any order, and a buzzer and/or fourth light comes on.

It's a simple circuit.  Must be.  Just a few transistors, LEDs and batteries.

But, I just cannot work it out!

I should be able to sketch it out in my sleep, but my brain will simply not cooperate.

I'd prefer to use a single DC power supply, up to 12V (multiple LEDs to make the lights brighter), but I have several I can use if required.

Dimensions are not important, I'll just change the lengths of wires.

But, can you help with the circuit?


Thank you, Lemonie!

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lemonie8 years ago
Right, I've never watched X-Factor, but I think you want:
Each of three switches to light their own light independently.
All three switches to power a buzzer / 4th light?
Get three double-pole double throws, and wire like this.

>gives lemonie a vicious kick for coming up with a better idea and schematic before I was about to post another<

Kiteman (author)  Lithium Rain8 years ago
I was all ready to go for a set of self-latching relays...
I made it all pretty, with a three way AND gate and everything.

Kiteman (author)  Lithium Rain8 years ago
Hey, you can still post it, especially if it's all pretty.
I have to agree with Jayefuu here too;  without something like a 555 timer, you will have to reset the buzzer manually, or reset everything to cut the buzzer, since it is latching. 

If the switches trip the timer (monostable multivibrator) which trip the buzzer, you can set the duration of the buzz time.
Jayefuu Kiteman8 years ago
Don't forget a monostable otherwise that buzzer's going to be going off FOR EVER and be really annoying :D
That's a very good suggestion.
lemonie Kiteman8 years ago
If you want something with big red plastic single-push non-latching buttons that light-up and a master-reset, the question is still open...

Kiteman (author)  lemonie8 years ago
I'm now waiting to find out my budget - latching DPDT push-switches are available on ebay.

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