Bellman's Toil PLC Control

As part of a major project to replace some of the oldest rooms of The Gravesend Inn haunted hotel attraction, we ended up with the "Bellman's Toil" effect that didn't fit into the theme of the new room. So, we decided to take the pieces and make them into a stand alone effect, which doesn't require the massive control infrastructure of the The Gravesend Inn, and can operate year round.

Since this is a simple show control system for a simple linear show (see my book for more information) controlling only pneumatic effects, two lighting circuits, and two audio sound effects, I decided to control the whole thing from an Automation Direct DL105 Programmable Logic Controller (PLC), which costs only $179:

I picked an Alcorn McBride Digital Audio Machine (DAM) to play back Bruce Ellman's audio effects; you can see the DAM in the lower left of the cabinet in the picture below. The DAM model we picked has a built in amplifier, and uses a compact flash card for playback.

The orange box on the upper left is the Alcorn contact closure break out; to the right of the PLC is 24VDC distribution and fuses for the lighting effects. On the next DIN rail down is the DAM power supply, AC distribution, and then a transorb:


This transorb shunts the back EMF from the 24VDC solenoid valves turning off, which Automation Direct says can exceed -300VDC!  Without the transorb, each time we turned off the pneumatic valves, the Digital Audio Machine would go into some crazy fault mode, and I'd get very erratic behavior from the diffuse reflective sensor we are using.

I used the "drum instruction programming" elements of the Automation Direct ladder logic language:

In the drum element in the middle of the screen, you can see a grid. The rows in the grid represent steps in the "drum"; the "K" numbers to the left are the times, in 1/10ths of seconds, for each rung; the columns represents the six individual effects (pneumatic 1/2, lighting 1/2, and sound fx 1/2).  A black dot in a grid position means that effect is on at that time.  The effects are to be mounted behind plexiglas for safety reasons, and there is only one Run/Stop control on the box:

Here's a little video of the test setup (the automatic gain control and test setup make the pneumatic valves sound MUCH louder than they will be in the finished product):


I designed the system and our "special wiring projects crew", headed by Erin Grabe, laid out the cabinet and did most of the wiring and mounting.


Pictured: Students Lillian Jimenez (left) and crew chief Erin Grabe; not pictured, James Palermo, and draftsman Evgheni Goncear.  More pictures here.