I was asked to build some props for a friend's liveroleplaying game.
They either had to look ancient or modern and should work without any gamemasters intervention.

This one was one of the moderns and was used to turn on a plasma disc by basically activating a relay to let the current flow.

Step 1: What Parts Did I Use

Everything i used, i got off from ebay, so i cannot even specify a vendor.

- 3 plastic cases ( to hold the electrics )
- 10 on-off-on switches
- 2 RCA male connectors and 2 female jacks
- 5V relay
- 9V battery
- some LEDs
- wire

Step 2: The Switch Boxes

The main purpose of the switch boxes was to close a circuit and let a current flow from the attached RCA plugs inner ring to the outer ring. Closing circuits and plugging it in to the "Relay Box" ( next step ) will trigger the next steps.

I decided to use switches with three positions, on-off-on, to make it a bit more difficult.
As well as a second switch box :)

First of all i used a standard wood drill to drill holes in the box and positioned the switches.
The plastic cases are halved and connected with screws, which makes soldering and modifying very easy.
Then i soldered the switches contacts in a random order to create the solving pattern.
The last switch got an RCA plug connected, that will be used to close the overall circuit.

The knot in the RCA cable is important, since it serves as the strain relief and you don't want to rip it out.

Step 3: Remember the Combination

I am very forgetful person, so i decided to take a picture of both switch boxes in a state, where the circuit is closed.

Step 4: The Relay Box

This is the core part of the puzzle, since it holds the relay, that activates the plasma disc.

The Relay Box consists of five parts:
1.) the power cable
2.) the relay
3.) the 9V battery
4.) the RCA plugs
5.) four LEDs

The power cable is the standard power supply shipped with the plasma disc, supplying 12V DC. I cut it in a half, connected the ground cables again and attached the V+ cable to the relay ports.
The 9V block powers the relais itself. It only needs 5V, but seemed to be tolerant enough to also work on 9V. Still, i recommend a matching power source. Once the relay is triggered, the disc turns on.

The actualy triggering happens through the switch boxes, that are now attached to the RCA plugs in the relay box. If the switches are in the correct position, they close the power circuit of the battery, so the relay is triggered and the disc gets powered on.
Usually, the relay is activated by a high level on its control pin. I decided to connect the ground and the control pin to induce this high level ( 9V in this case ), which worked fine.

As soon as the circuit is closed, four LEDs get activated and two acrylic glass sticks glow, that are attached outside the box. This was just to make it a bit more fancy :)

Step 5: Test the Setup

Step 6: The Final Picture

The puzzle was part of a larger prop of the events ending scene. Just to provide to full picture.
It looked way better in original, since the lighting was not yet done, when i took the pictures :)