Servo - December 2015

24 SERVO 12.2015 then determine the delay between triggers so that everyone has a chance to see your character in action. The downside to this method is that if there is a break in your visitors, your prop is still going to activate.

Pushbutton

If you are fortunate enough to have someone available to monitor your prop, you will probably want to use a pushbutton trigger. This method is virtually foolproof and gives you the ability to choose the optimum trigger point. Oftentimes, you don’t want the first person to trigger your routine but would like to delay its activation until your intended victim arrives. Building a wired pushbutton is a simple do-it-yourself project. If you’re interested, check out the one at http://tinyurl.com/ooupa6z.

There are also plenty of wireless models available that activate a relay which can be connected to your character and used to activate it (Figure 1). The most precise choice is often to have a person on hand that activates your character at exactly the right moment. However, we often do not have this luxury. In those cases, we need to find another solution that will accomplish the task.

Step Mat

A step mat is easy to use, reliable, and can provide a very accurate trigger point. These work the best in darkened hallways where you can control the path your guests will take. The biggest drawback of these triggers is that they can easily be avoided. Properly disguising them is a must! Installing the mat under carpet if indoors works well. Do not just lay it out on the sidewalk and expect it to be effective. If you use it outside on a trail, try burying it under a thin layer of leaves. You may even want to further camouflage it by painting it and gluing a few leaves to the top to help hide it if the covering leaves are displaced.

Making your own step mat is an easy process that requires only some cardboard, aluminum foil, and wire, along with a little time. Check out the example at http://tinyurl.com/nat36ke or purchase one like this from Monster Guts (see Resources).

IR Light Barrier

A break beam such as the Velleman MK120 can be another good choice when you are able to channel your guests down a specific passageway (Figure 2). It uses an IR emitter to send a beam which is bounced off of a receiver on the other side of the walkway. This gives you very precise prop activation, but does require the placement of two components that need to stay aligned to work. Select a mounting location where you can conceal both pieces at the proper height. You also want to be sure they are securely mounted so they cannot be bumped into and moved out of alignment. A very useful modification to this kit can be found at http://tinyurl.com/yea9le4.