# Game Show Buzzer Help!

#### TheArmondo28

Joined Nov 12, 2011
4
Hi,

Basically I want to create a buzzer system for a game show I am holding. In this buzzer system, I want to make sure that only one buzzer works at any given time, so that the first person/team to hit their buzzer will have a led light lit and any other person/team to hit their buzzer after this will have no light lit. In essence, the basic buzzer system used for any quiz game.

I am a newbie when it comes to working with circuits. So I would really appreciate it if someone could explain to me how to set up such a buzzer system with about 4 different buzzers. Please explain in laymen terms.

Any help would be greatly appreciated. The already setup buzzer systems are way too expensive for my budget, that's why I want to make my own. I have very very very basic understanding of circuits (if that helps).

Thank you,

#### Georacer

Joined Nov 25, 2009
5,182
You should work with logic gates. Each button should be ANDed with a control input, to decide whether the button will be enabled or not. If another gate is previously enabled (and latched on), then the AND gate input should turn to '0', disabling the button.

For a four button circuit, I expect a cost of at about 10\$ at the most, buttons not included.

Is that clear, or do you need more information?

#### absoluteZro

Joined Nov 12, 2011
19
My technical knowledge is very limited (non existent?), but If I were faced with this problem I would go about forming a loose idea of what might be required. This is what I came up with while I should have been doing my thermodynamics homework, because I wanted to figure it out.

If you have everyone at a table, you could have each person with a buzzer. What I'm thinking is, you have a basic circuit connected to a battery, with the wire going through each buzzer.

The next part is inspired by remotes and keyboards and whatnot:

Each buzzer has a switch that will open the circuit when pushed, thus disconnecting the other buzzers. But you want the light bulb to flash so you know who hit first. So when the buzzer is pushed, it will first connect the light bulb to the circuit, then disconnect the circuit so no one else's light can flash. You can use a spring to make the buzzer harder to push down. Also, perhaps include a notch that will keep the buzzer down until it is released by the player, so the circuit remains open till the next question. Or to make your life easier, tell players to keep holding down the buzzer.

For knowing the values for voltage, current, and any other things: sorry but I can't help without doing way more work than I would like.

Good luck. I attached a picture of a rough idea of what I explained.

I think this is a good system for someone (like myself) with little electronics experience. It is very very simple.

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#### KMoffett

Joined Dec 19, 2007
2,918
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#### Georacer

Joined Nov 25, 2009
5,182
KMoffett, can you explain to me what will prevent another contestant to activate his light in the circuit you posted?

Thanks.

#### KMoffett

Joined Dec 19, 2007
2,918
Sure! With no responses, the low resistance main lamp, Zener and resistor in series allow enough voltage drop across the resistor to trigger an SCR. Once one SCR is triggered the main lamp and the contestant's lamp are placed in series across the 12V supply. Since that only allows ~6V across the contestants lamp and SCR, the 9V Zener will not conduct. There is then no voltage drop across the resistor and the other SCR's cannot be triggered. Elegant, isn't it!
The caveat is that the SCRs be of the "non-sensitive gate" type.

Ken

#### TheArmondo28

Joined Nov 12, 2011
4
Hi KMoffett,

Thanks for sharing that link! But to be honest, I am really confused on what they are saying. Is there any way you can explain the details in layman terms. I would like to have about 4 different stations. These 4 different stations are not right beside each other, they are at different tables.

Sorry for the trouble!

Thanks!

#### TheArmondo28

Joined Nov 12, 2011
4
Hi absoluteZro,

Thanks for sharing your input! You said that it was very simple, but I'm having trouble setting up this circuit. Can you please explain in a bit more detail of how to set this (i.e. how to connect the things together).

Thanks!

#### KMoffett

Joined Dec 19, 2007
2,918
That circuit requires wires between stations. You won't find any simple system that doesn't require wires to connect the contestants.

Sorry, but unless you have at least little basic knowledge of electronics, it would be too much for me to explain that "simple" circuit.

Ken

#### TheArmondo28

Joined Nov 12, 2011
4
Hi KMoffett,

I understand that this requires wire connection, and I have a basic understanding of circuits. It's just the circuit diagram from that website was really complicated for me. So I was wondering if you can break it down.

I have taken physics at the university level where I had to learn about basic circuits. That should give you an idea of my knowledge regarding this. I really hope this method does not involve soldering - because I have no idea how to do that.

If you can simply what that website is saying, I'm pretty sure I will catch on.

Hopefully, you can help out.

Thanks!

#### absoluteZro

Joined Nov 12, 2011
19
My knowledge is probably where you are at, sorry. I have only taken university physics. But if you read that guide, it explains the setup really well. Use google to search for any term you don't understand, that's what I did. Also, if you have the parts it might be easier to understand what they are saying. And...I think soldering will be necessary.

KMoffett, I'm in the same boat as him. To you, that circuit may seem simple, but wikipedia does a poor job of explaining what a triac/SCR will do or how they operate, or how to decide on which to buy.

I think I understand the basics of that circuit, however, I don't understand how the parts do what they are doing. I don't think it's all that simple. My first confusion:

With no responses, the low resistance main lamp, Zener and resistor in series allow enough voltage drop across the resistor to trigger an SCR.
I don't think I understand the link between the voltage drop and the SCR. From what I read, the SCR is triggered "When the gate-to-cathode voltage exceeds a certain threshold" (wikipedia). So what is doing the triggering here? If the pusher is doing the triggering, how is that connected to the voltage drop?

If I am misunderstanding too much and you don't want to explain, that's fine. Just tell me, and I will keep reading things elsewhere.

#### praondevou

Joined Jul 9, 2011
2,942
Hi,

I redrew the circuit so that the wiring may get a little more visible.

As for how the circuit works: Actually Ken explained it all.

Initially no triac/scr is conducting, so there is no current through them. So initially just forget about them.
There is a current flow through the main switch (closed) the main lamp, the zener and the 100 Ohm resistor. A current through a resistor means there is a voltage drop over it, which you could measure with a multimeter for example.

As soon as someone pushes the button this voltage is applied to the gate, current flows from the power supply through the main lamp, the zener into the gate, thus triggering the SCR. The SCR conducts now, the lamp in question turns ON. Now there is a current through the main lamp and the lamp whose SCR just turned ON. 12V are almost divided by two (there is a small voltage drop on the thyristor), i.e. now you have less than 9V from zener cathode to minus of the battery.

This means the zener does not conduct, no current flow through it means no voltage drop on the 100 Ohm resistor. If anybody else presses a button there will be no voltage/current available to trigger it's SCR.

I know that I essentially repeated what Ken said, just using different words.

There are two things you need to know about an SCR, it acts as a switch, once you trigger it, it will remain ON as long as the current through it is higher than it's holding current. This is the second thing. There is a parameter called "holding current". So when choosing an SCR/triac you have to make sure that enough current will be flowing to keep it it conducting. The holding current for the SCR proposed is 30mA. The lamps have 4.5W from what I've seen so their current is higher than this.

If it helps, THIS is the datasheet of the proposed SCR.

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#### KMoffett

Joined Dec 19, 2007
2,918
The attached shows the changes in voltage from the initial state to the first push to the second push.

Ken

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#### absoluteZro

Joined Nov 12, 2011
19
First, this site is AWESOME. Those were extremely informative, and I went in knowing nothing at all.

So, I read both the Shockley and SCR pages, and then the Zener page.

Now I will try to explain the circuit how I understand it from the site diagram, and from KMoffet's diagram (the one I actually understood). Tell me if I am wrong.

The 12v battery is initially putting enough voltage, even after the resistor, to "break down" the diode and travel through it. This leaves what you calculated as .43v to drop over the light bulb, right? (it shouldn't light up at that voltage right?)
Then when a switch is pushed (what is the term for switching to connect a circuit?), initially, the zener will drop 9v, the gate will drop 2.5v(?), and the main light bulb .43v. But almost instantaneously the SCR will be triggered allowing current through, the zener will be taken out of the circuit, and the resistor too, since the light bulb1 will now be using 5.89v, and 12-5.89v=~6v<9v for breaking down the diode. And 6v will drop across the main light bulb. If another player presses the switch, they are connecting their SCR gate to a part of the circuit that has no current, thus nothing will happen. When the top switch is opened, the voltage drop at the SCR will go to 0, and it will stop allowing current. Close switch, and everything is back at the start.

Now my question: I only half understand the reason the other players cant light their bulbs. If the gate is opened, then why wont current go through the resistor and through the gate? is it because there is already a circuit dropping all the voltage?

#### KMoffett

Joined Dec 19, 2007
2,918
Good analysis.
...
Now my question: I only half understand the reason the other players cant light their bulbs. If the gate is opened, then why wont current go through the resistor and through the gate? is it because there is already a circuit dropping all the voltage?
With only 6v across the series Zener and R1, the Zener does not conduct and there is no current through R1 and there for no voltage drop. Now the gate switches, when closed, are pulled to ground by R1, not to +2.5V. Since the SCRs' gates can only be pulled to ground, no gate current flows, and no other SCRs are triggered.

One thing I liked about this circuit, is that the contestants' stations can be either "starred" or "daisy-chained" depending on the number and locations of the contestants. I've used combinations of both. Actually, I used one of the two-wire versions for a "professional" setup. Everything was linked with low-voltage coaxial power connectors. For the three-wire versions you could use 1/8" stereo phone connectors.
ken

ken

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