A Spooky Graveyard Show For Halloween 2009


Halloween 2009 update

Taken me ages but here they are


Video 1

Video 2

Video 3


Last Halloween I put on a spooky graveyard show for visitors to the house. I made some fake gravestones out of hardboard
and painted them with grey primer. Behind these at ground level I placed a 150W halogen floodlight with green filter
which was connected to a 12V relay driven from a PC.


This relay was a single pole double throw type and also connected to a strobe light so that when the flood light was on,
the strobe was off and vice versa.


A smoke machine controlled by the PC with an adjustable mark space ratio provided a nice fog effect.


The PC played spooky music through some outdoor speakers and was wired to the doorbell so that when it was pressed,
the flood light was turned off, the strobe light turned on to simulate lightening and a thunderclap played.


All thought it was great fun. Here are some videos made by a CCTV camera mounted above the gravestones.



This year I decided to do the same show, but with a full size coffin, complete with skeleton, placed near the door.


As trick or treaters(?) approach the door, a passive infra red detector will signal the PC to open the coffin lid with
a creak to reveal the skeleton inside the coffin which is illuminated with green lighting.


When the doorbell is pressed, the skeleton will rise; ĎNosferatuí style as the lightening and thunderclap play.


Starting Out


I obtained a rubber skeleton by mail order. Itís 5ft high so a bit short but convincing enough.
Anatomically itís a disaster but so what.

It is quite heavy, and I need to raise it quickly so I obtained a 250mm stroke pneumatic cylinder from ebay:





This will produce around 65 pounds of thrust so is suitably powerful.


The skeleton is mounted on a lifting bar which is a 5ft length of 2”x1.5” wood, the end of which has a hinge
attached. A second, 12” piece attaches to the other side of the hinge to form a mounting point for the
cylinder. The lifting pneumatics are hidden within a plinth.


Here's a side view plan of the coffin


Coffin PLan


I made a foot clevis for the cylinder to mount on from 1.5mm sheet steel. The moving end of the piston has a rod clevis attached
which is used to connect to the skeleton lifting bar.


Here is the lifting cylinder with rod (LHS) and foot (RHS) clevis attached:




Here it is fastened to my Workmate for a test with a rather bemused younger son in the background.



I constructed the plinth from 9mm ply and painted it grey to make it look like stone.


I fitted the skeleton raising hardware and realised that the force required to lift the skeleton was warping the back
panel of the plinth so I added some reinforcing struts.

Here's a picture of the plinth with the lifter bar raised.

And a close up of the lifter bar mounting. The two pieces of wood next to the lifter bar screw into the sheet of wood that
covers the innards of the plinth. The helps to further reduce the torsion on the back panel of the plinth.



I made a coffin out of more 9mm ply. It is 5ft 5ins high to give plenty of room for the skeleton. The angles formed
from pieces of wood cut to match the depth of the coffin. I then cut these to the correct angle on my table saw.
The coffin depth is 12ins which gives plenty of room for the skeleton.




The lid is raised by the smaller pneumatic cylinder below which is mounted within the coffin.

I made some mounting hardware out of 1.5mm plate steel to allow me to attach it to the coffin lid and walls.

There is a steel hinge at the LHS to allow the piston to swivel.



Getting the correct positioning for this
was tricky and it took a few goes before the lid closed properly and opened fully.


Here it is mounted within the coffin:




Pneumatic control

I use two 12V DC solenoid valves to control the cylinders. I got these from ebay but had to search
around for 12V ones as the normal voltage is 24VDC.





Coffin Lighting

It occurred to me that in a dark environment it might be difficult to see the skeleton so I made two LED strips
to run along the inside of the coffin. Each is a row of 5 x 10000mcd green LEDs which will be illuminated as the coffin starts to rise.


Here is a picture of the LEDs illuminated:


And a close up:



Control Board

I then made a small board with all the pneumatic bits attached. Each cylinder has a one way restrictor attached to the cylinder input.
This allows unrestricted air flow into the cylinder, but restricts as air attempts to come out. As both the lid and the skeleton return to
the default position by gravity, I needed to be able to ensure they fell slowly to prevent damage and this is what the restrictors do.



Itís no thing of beauty but its better to have everything fixed in one place.


A schematic overview of how everything is wired together.





Video of the coffin in action before I painted it:





Controlling Software


I used the PC parallel port to control everything as itís a nice, simple interface with 12 outputs and 5 inputs when
using it in its simplest mode. Some time ago I made a PCB with inputs and 500mA outputs on it.



This board uses ULN2803A darlington drivers which can be driven directly from the 5V output of the PCs port. These driver chips
have built in diodes to protect the darlington circuit from the back EMF of the relays/solenoids when they de-energise.

The outputs feed to screw terminals for easy connection and have LEDs to assist with debugging.
The inputs have switches attached so I can easily simulate inputs when debugging the software.


The software to drive the system is written in C++ with Visual Studio Express and uses SDL for the audio playback. The parallel
port is driven using the PaPic class from CodeProject.

I've decided that it is potentially too scary for smaller kids, so I've designed the coffin to work in three modes:

  • Green: No lid opening or skeleton rising
  • Amber: PIR detector cause lid to rise. No skeleton.
  • Red: PIR causes lid to rise, skeleton rises if doorbell pressed.

With this system I can dynamically control the show as required (I'm going to remote desktop into the controller PC from a laptop).
I've added a 'demo mode' override that will enable the full show from any mode. At any stage the system can be reset with a physical reset switch.


The software to drive the coffin needs to implement a state machine to make sure that everything is sequence correctly. I used StarUML

to produce a state chart for it.




Dry Run


I selected some audio tracks from a Halloween CD I got in a thrift shop last time I was in the US. The PC plays a selection
of tracks on a continuous loop as background music.


I knocked together a plan of how the system will be laid out:



Hereís an operational overview:


As the PIR detects victims approaching the house, the background music is silenced and a Ďcreakí sample plays. At the same time the internal coffin
LEDs are illuminated.


When the doorbell is pressed in red mode, the skeleton rises, the strobe light lit and the green flood lighting turned off. When the thunderclap
finishes, the flood lighting is restored.


The system resets from the coffin lid open or skeleton raised states after a timeout period. This is required in case a dog or other meat sack
triggers the PIR without making it to the doorbell.


Iíve got two remote switches placed inside the house so I can remotely reset the system at any time, or engage a Ďdemo modeí which allows me to
demonstrate the system when in green or amber modes.


I made a video of the dry run I performed last Saturday night (17 Oct). Note that the strobe light does not show up very well in
the video due to the short duration of the flashes.





From this test I now know I need to:


  1. Change the green backlighting. The flood I have is too directional. I think Iíll use a standard 150W halogen flood with a green filter on the day.
  2. Change the coffin lid opening sample.
  3. Move the PIR a bit nearer to the door. This is because I couldnít hear the coffin lid sample as the PIR triggered.
    This may not be required after Iíve changed the sample.
  4. Check the length of the thunderclap sample. I think the strobe may be being turned off too soon.