This is the classical quiz game system, with three big red pushbuttons.

The circuitry is only made of relays and diodes (and some additional components), there is NO INTEGRATED CIRCUIT NOR MICROCONTROLLER so this project can be made by who hates them !

The interesting thing is that the electromechanical circuit is a skeleton onto which you can build, in a future, an eventual digital/computerized management. In fact, an optional "option" connector is included (but not used by now).

What is this:
There are three quiz stations, each with a big red button and a led strip used as luminous indicator. The first competitor that pushes his red button "wins" the faculty of answering the presenter's question. When you press the button of course the other two stations are disabled and only the presenter can enable them again.

What you will need:
- Three big red buttons, or similar big button. They have to be Normally Closed (NC). If you use Normally Open (NO) buttons you should make significant modifications to the schematics (not descripted here).
- Three led strips, 12V, or some other kind of luminous indicator.
- Some pieces of wood panels and eventually paint, it depends on how you would make the basement of the quiz station. You could also make three podium or something like this. In my case I've made only three boards with a vertical wooden part for the led strip.
- A box or enclosure for the controller.
- Three connectors for the stations, I have used 5pinXLR's, 3 male cable mount and 3 female panel mount. Optionally a DB9 female connector.
- Two or more switches, 12 diodes (1N400x would be okay), 3 12V relays, a power supply already made (12V-2A) or a transformer, a rectifier and a capacitor to build it by yourself, some resistors, two NPN transistors and two capacitors (see schematics in the next step).
- Tools and patience of course. Soldering is needed, also hot glue would be glad.

Step 1: Schematics

Some comment about schematics. Skip this step if you want to build without understanding :)

The goal of the system is this. The competitor reserves to answer the question by pushing the button, his lights turn on and a sound is emitted. Immediately the other stations are disabled, until the presenter resets the system.

To obtain this behavior you may want to proceed in two different ways:
** microcontroller or digital circuitry : one or more chips on electronic board are enough to make the logical part of the “quiz system”. PRO: fully customizable, cheap (especially for on-scale production), centralized. CONTRO: more design time is needed, realization of one prototype needs time.
** electromechanical circuitry : the logic is reached through diodes and relays. PRO: cheap, easy to build, reliable. CONTRO: not for on-scale production, not customizable, complexity grows up with number of stations.

The second way was initially only a challenge, but then I've started to figure it out as the best choice. The interesting thing is that the electromechanical circuit is a skeleton onto which you can build, in a future, an eventual digital/computerized management.

Take a look at the schematics.

The relays are decentralized as they are part of the pushbutton/lamp system circuit. In this way the circuit is more logical and easy to build. The buttons are Normally Closed, so they keep the relay excited closing its circuit. When the button is pressed the relay is released so two things happen: the button-relay circuit is opened, so if the button is released nothing happens (this ensures precise survey of the push instant), and the other circuit is closed turning on the luminous indicator, the acoustic indicator, and forcing the others relays on. The last matter is achieved through a network of diodes. Of course, the more stations you want, the more complicated is the network. Last but not least, reset and inhibit switches (logically different, electrically the same) will force all the relays on, closing again their circuits until a big red button is pressed.

The part of the circuit where a microcontroller is most missing, is acoustic signal. It has to be limited in time so some kind of timer is needed. A microcontroller would have done this by software with no problems (…fully customizable… meant also this). The network on the bottom of schematics provides a good enough timer (not precise, because the Capacitors have to discharge between one reservation and the other), with the possibility of choice between short, long and none.

Step 2: Quiz Station Assembly

Firstly you have to build your own basement. I have opted for a very simple one, made with a wood board and a small piece of vertical panel for the led strip. Another possibility is illustrated (with google sketchup) in the image 4.

In my case I've cut a piece of plywood panel for the basement, and a piece of wood board for the vertical part. I've rounded the angles firstly with saw then with sand paper. I've assembled the two parts with vinylic glue and some screw.
If you want you can paint the basement with water-based paint.
In my case I've let the wood "natural".

Then you have to mount the base of the pushbutton with two screws and the LED strip with its adhesive plus some drop of cyanoacrilate glue.

If your basement is some kind of a box, all the wires may be passed inside, so they are not visible. In my case I was obliged to pass them on the surface making them visible. Note the small hole for passing the cable of the led strip. Also, there's a white hose hiding the wires of the led strip.

Finally make the connections with the relays (look at the schematics). The most important thing is finding the wiring diagram for the relay you are using. I'm using a GRUNER X1U-G320, and the spule contacts are the middle ones, the two apart are common (toghether). The other two are NC and NA contacts, and a tester is useful to find which is which.

At the other end of the 4-wires cable, solder a connector. I've used 5-pole XLR.

Step 3: The Controller

The controller is enclosed in a plastic box.

On the back there must be the 3 connectors for the 3 stations (i've used 5-pin XLRs), the mains connector (or the cable directly exiting, or a connector for external power supply if you prefer), and the "option" connector (optional).

On the top there must be one switch and one button for enable/disable and reset. I have used a combined rocker button which has three positions, center open, stable switch in one way and momentary button in the other way. There should be the switch for the acoustic alarm (optional, i've used three positions rocker switch), and there should be some indicator led: one for the system and 3 for the 3 stations. I have used bi-colour with two wire for the system.

Ok so make the holes, an additional hole is in the side of the box, for the buzzer. I have no main power switch as the device is intended to be detached from mains when not in use. If you use external power supply it is safer.

Mount all the leds, switches, connectors and the buzzer. For the leds and buzzer, hot glue will be very useful.

Follow the schematics and photos, all the resistors should be soldered behind the led's and switches. The few components for the buzzer timer can be soldered as a "dead bug", or you can use a small piece of breadboard if you prefer.

The 12 diodes should be soldered like a matrix on the back of the connectors. This is the probably most annoying phase of the build process.

Finally write the functions of the buttons and leds on the front panel, or printout a mask on adhesive paper as i have done.