Aug 052013
PropWatcher DMX Trigger Machine

PropWatcher DMX Trigger Machine – Click to Enlarge

Just in time for Halloween, we’ve got a useful new box to share with the world.

In the past, we’ve done quite a few contact closure –> DMX scene trigger systems for different customers.  This project, however, adds some new and potentially very useful features.

In its original incarnation, it was designed for triggering haunted house props.  The designers had scattered around a great collection of electric eyes, pressure mats and other contact-closure type inputs.  They also had a large quantity of solenoid valves, lights and other technology which ran the different sections of the haunted house.

This system allowed them to use a single system to accept all trigger inputs and drive all their prop outputs, simultaneously and in parallel with each other.  DMX is of course useful as an output bus because it can be driven great distances using fairly inexpensive cable, and because many DMX devices (relay cards, dimmer packs, fog machines, LED fixtures, etc) can be daisy-chained on the same set of wires.

Electrically, each of the sixteen input stages looks like this:

PropWatcher Input Stage

PropWatcher Input Stage

The input terminals are of course isolated from each other, and from the internal processor, with a sturdy optoisolator.  Any voltage between 5 and 24v DC can be connected to any input. We chose a durable Phoenix quick-disconnect plug for the trigger inputs.  Attach your wires to the screw terminals, then plug in to the chassis for a durable connection.  Makes setup and tear-down much easier.


There are two ways to use external sensors:

Input Schematic

Input Schematic

Each input has a unique set of timing settings which may be adjusted in 0.5 second increments as well:

Timing Settings


The Predelay   is useful if a trigger is located some distance from where the lights / pneumatics / etc are setup.  A trigger can happen, and then the system will wait the duration of the predelay to turn on the recorded DMX scene.  The On Timer of course dictates how long the DMX scene will be displayed.  The Loop Time is the ‘off’ duty cycle, and it can be set to more than 0 seconds if a repeating effect is desired.  The DMX scene sequence (which takes on and loop times to display) is then repeated for a certain number of cycles.  Finally, each input can be in Lockout mode for a certain time (the input trigger is ignored) to prevent effects from being triggered too frequently.

All sixteen inputs run in parallel, which means that any effect or combination of effects can be triggered at any time.  All unused / unassigned DMX channels are always set to zero.  So it’s very easy to use groups of 1-10 channels for each trigger input.  Since all the trigger inputs run simultaneously and in parallel with each other, having multiple triggers be active in different areas of the attraction is no problem.

Finally, the system’s menu and pushbuttons make it straightforward to assign DMX channels to a particular input, and set their respective levels.  The theory here is that in most situations, each location will consist of a trigger input and 1-10 (or more!) DMX channels as output.

Since the system isn’t PC based, it boots in 2-3 seconds.  Also, the firmware can be upgraded in the field using a convenient USB port, should new features ever need to be added.

Here’s a quick and un-edited demo video of how a few inputs can be quickly configured and used:

Questions?  Thoughts?  Tell us in the comment section below.

 Posted by at 9:38 pm

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