Trigger Relay

We use a lot of X-10 to remotely control props in our haunt. This sometimes makes hookup complex because (a) we often want to trigger more than one thing at once, like a popup, strobe, and sound (b) the sound boxes like to be triggered with a simple switch closure, not 110 VAC line current.

We solved both problems by combining a relay (an electrically operated switch) with a cube tap.

WARNING: This project uses line voltage, and is hazardous. If you are not qualified to work on projects like this, please do not attempt it. Get help from somebody who is qualified.

Background
Solution
Parts
Safety
Assembly
It's so simple. Is it really useful?

Background

A relay is an electrically controlled switch. Relays are pretty handy:

A relay provides isolation from one electrical circuit to another.
A small coil voltage can control a large load. This is usually how computers control the outside world.
A high control voltage can control a low load.

We'll be using a relay in that final context: the X-10 remote switches can control line-level power; piping line voltage into a little scream box would blow it up. The relay lets us control the little scream box with 110 VAC.

Furthermore, we know that we will want to control more than one 110 VAC gadget, so this includes a power-distribution system (a cube-tap).

Solution

Our solution is designed to provide both a switch-closure output and to share the wealth of 110 VAC power. We do this by taking a commercial "cube" current tap that allows you to share power, and adding a relay to it to trigger the prop.

This is similar to our line voltage switch and Gemmy fogger control.

Parts

Please see purchasing electronic parts.

The relay used in this project is Radio Shack #275-217. It features a 110 VAC coil and DPDT contacts rated at 10 Amps. As of January 2002, it sells for $7.99.

This is a similar relay with identical specifications, made by NTE. I bought this one in January 2002, for $7.99 at Fry's.

Given that we are using this relay to trigger a small device, those contacts are overkill (and overpriced). Just about any relay with a 110 VAC coil and at least one normally-open contact will do. The relay we that we used in line voltage switch and Gemmy fogger control would have done fine, and it only cost $.99, mail-order. A different relay may have different electrical connections than the one pictured.

The other major component is a "cube" current tap.

Don't get one that is molded in one piece. Get one constructed of hollow plastic that can be opened up.

The cube tap can be two-prong or three-prong, according to your needs.

Assembly

Assembly is trivial:

Open up the cube tap.
Tap into the cube tap by soldering wires to the "hot" and "neutral" sides of the power line.
Run the wires outside the cube tap, through one or more small holes drilled in the body.
Close the cube tap back up again.
Glue the relay to the cube tap.
Solder the wires from the cube tap to the relay coil terminals. Use heat-shrink tubing to insulate exposed metal. Any exposed metal on the "coil" side of the relay is a shock hazard!

Now, whenever the cube tap gets power, the relay closes. Just hook whatever you want to control to the relay contacts.

This is the completed trigger relay assembly.

Note the two discolored areas to the left and right of the prongs. This is where epoxy glue was used to seal the cube tap back up.

Note the red heat-shrink tubing to insulate the coil side of the relay.

Safety

This project deals with potentially hazardous line voltage.

Any exposed metal on the "coil" side of the relay is a shock hazard! Use heat-shrink tubing to insulate all exposed metal.

If the load being switched is low voltage, the output side of the relay can be left exposed. This facilitates later selection of normally open versus normally closed, and the use of multiple poles.

But if the load being switched is not low voltage, any exposed metal on the output side of the relay is a shock hazard! Use heat-shrink tubing to insulate all exposed metal.

It's so simple. Is it really useful?

Actually, it is.

We use one for our popup skeleton. The relay output triggers a canned scream box. A strobe, amplified speakers, and HAM all plug into the power cube. We just have to hit the trigger relay assembly with 110 VAC, and everything goes off at once.

We do the same thing with our pumpkin popup.

The giant spider gets slightly different treatment in that her amplified speakers are plugged into an unswitched outlet so that she continues to make noise when the power is cut and she moves down.

Thank you for visiting. Your comments are welcome.
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