Saturday, 7 November 2009

Post Halloween Video

Halloween has come and gone. Very favourable response to the show but only two videos worth watching. I've had real problems with the audio on these. I had to record the audio on a camcorder separate from the video recorder and had real problems synchronising the audio and video.
It turned out that the video was running at 60Hz and the audio at 50Hz so I had to use Audacity to change the audio lenghth by -20%.

Here are what I call 'screaming runners'



Sunday, 25 October 2009

After last weeks dry run I realised that the 300W stage flood I got from Ebay was too directional. I decided to go back the 150W halogen floodlight I used last year:

The problem with last year was that I sandwiched a green lighting gel inbetween the lamp housing and the class cover. Although lighting gel is rated for high temperature operation the gel I used ended up like this:

The bit in the middle was blackened and really attenuated the light output of the lamp.
Hoping that this was caused by thermal conduction from the glass plate, I made a steel
gel mount to mount the gel in front of the lamp with a 10mm air gap between the glass and the gel:

It's a pair of steel plates that bolt together, sandwiching the gel between them. It then mounts
on top of the floodlight:

I ran it for 3 hours without any obvious degredation to the gel.

Sunday, 18 October 2009

Dry Run

On Saturday night I managed to set the complete system up and do a dry run. I resurrected last years grave stones and set everything up more or less as detailed in the last posts diagram.

I videoed two system operations. One with lights off, which is how I intend to operate the system on the day. This does not show up very well on the camera though.

Another issue is that the strobe light does not show up on the video very well. It looks fine in the real world though.


The second run was with the 150W floodlight at mounted on my garage turned on. This shows up much better on the video but does not appear quite as spooky.


Here's what I've learned from the execercise:
  1. I'm not sure about the 300W floodlight I'm using. I feel it is too directional. I think I'll try a 150W halogen flood.
  2. I need to change the coffin lid opening sample, you can hardly hear it. nophead suggested that I record the squeaky door in trap 2 of the gents toilets at our workplace. So not feeling at all a bit pervy I started recording stuff in there with my phone, and just for the record, I was alone.
  3. I think the PIR may need to be closer to the door.

Roll on Halloween.

Friday, 16 October 2009

Dry run planning

Tomorrow I plan to do a dry run.

Here is a plan of everything as it will be laid out on the day:

My drive, and my neighbours run parallel, he's told me he won't be in on the night of halloween so his drive will be clear. I will also make sure my drive is clear to enhance the spookiness.

I've also drawn a plan of the electro-pneumatic system to give me a rough idea of what I need to wire up:

The two wierd symbols inbetween the pistons and the solenoid valves are the one way restrictors that allow the skeleton/lid to reset under gravity without excessive speed.

The flow restrictors allow me to control the acceleration of each piston.

The control software is complete. The only thing that needs to be done is time the up/down times of the lid/skeleton so I can ensure the software waits for sufficient time before transitioning to a new state (e.g. CoffinLidOpen).

I also need to make sure that the audio sample I have for the coffin lid rising lasts long enough for the lid to rise. I plan to use the excellent 'Audacity' to stretch/shrink the sample time without affecting the pitch.

Wednesday, 14 October 2009

Making progress.

I've been working on a distribution board for the coffin. It takes the output from the PC driver board and feeds it to the coffin LEDs and solenoid valves.

It's no item of beauty but it works:

The hardware is now complete. I'm hoping to do a dry run this weekend.

Sunday, 4 October 2009


I have made some led strips to provide an eerie green illumination within the coffin as the lid opens. They are strips of 9mm plywood with five 10000mcd 10mm LEDs attached. I've split them into two parts to allow them to be fitted along the edges of the coffin.

Here is a picture of the LEDs illuminated:

And a close up:

The LEDs will be illuminated as the lid starts to open, and turned off when it has closed.


It's been pointed out that there is an uneccessary transition to the reset skeleton state from the coffin lid open state in the statechart below (thanks Richard). I've re-drawn it and added another state to play a 'creaking door' sample as the coffin lid opens.

The state which opens the lid without playing a sample is used when the lid opens from the doorbell button. At this time the thunder sample is playing and the creak sample would be inaudible.

Here is the new statechart:

Thursday, 1 October 2009

Coffin time

I've been working on a design for the software to drive the coffin. 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.

Here is a StarUML state chart of the coffin state machine:

Saturday, 26 September 2009

Assembling the real thing

Today I started to put the rest of the wood together to form the coffin plinth. 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 pic 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 also fitted the coffin lid and the lid lifting mechanism. Here the skeleton lifting bar is in the down position with 'Albert' attached.

Here's a video of it working:


Busy week

I've been busy. I've spent the last few evenings assembling the electronics that will enable me to control all the pneumatics from a PC. I've made two mistakes on the board design:

1) The linear regulator holes were too small. It was a simple job to drill them out to the right size but this removes the through hole plating, the result of which is that I've had to solder the pins top and bottom.

2) I got the pad spacing of the 25 way D type connector I was going to connect to the PC with completely wrong. So wrong that the conenctor I wanted to use will not fit in the holes. Fortuanately I had some 25 way cable lying around (as one does) and I've soldered this cable directly to the board and put a connector on the other end to plug into the pc.

Here's a pic:

Sunday, 20 September 2009

Coffin time

Got some 9mm plywood yesterday and started on building 'the coffin'

Thursday, 17 September 2009

Fast boat from China

The printed circuit boards I had made arrived today. They are good quality and four turned up when I only paid for one! Not bad considering I only placed the order on the 4th Sept. and they have been made in and shipped from China!

This sometimes happens when they have a big space on the PCB blanks that they use. It is cheaper for them to fill as much space as possible and so if they have a small design (like mine) that can fill the gaps with they will use it repeatedly.

Good news for me as the boards work out at £11.50 each. Can't argue with that.
Trouble is though, I seem to have got the silk screen over the pads on one of the surface mount footprints. Ah well.

Now where's that soldering iron?

Saturday, 12 September 2009

Raising the dead

I've had to abandon my plan for skeleton raising as detailed in my last post. The forces required are just too high. The problem is that with the lift bar flat, the force required to get it moving is considerable. My piston can just about supply this, but once the lift bar starts to move, the force required to elevate it decreases as it rises from the horizontal. As I cannot reduce the cylinder pressure once the bar is moving then this extra force results in acceleration, the outcome of which is I've made a siege engine.

Here's my test rig with the full length lifting bar installed:

I've only dared to run it once, which resulted in plan B. This involves having the pneumatic cyclinder at 45 degrees ish to the lift bar. This means that the skeleton coffin will have to be on a plinth to accommodate the cylinder. Not a problem.

Here's a video of plan B with the recently arrived 'Albert'

Note the slightly bemused Matthew in the background.


I was pleased with the damping effect as the system returns to the start position. I have some 'connectors' that limit airflow in one direction only. The system returns to the start position under gravity and the damping effect is caused by a build up of pressure within the cylinder as the piston compresses the air within it.

Tuesday, 8 September 2009

(Almost) Raising the dead

Finally the rod clevis for the end of the skeleton raising cylinder arrived today:

Here it is attached to the cylinder complete with foot clevis at the RHS and plates to mount to the lifting bar at the LHS.

Here is a highly technical plan of what I'm trying to do.

After a test run my rig failed to lift anything, then almost destroyed itself as I increased the pressure. Due to the short distance between the hinge and the piston attach point then once it got going the unhinged end of the lift bar went too fast.

I am going to have to maximise the angle between the cylinder and the base plate as the piston attaches to the bar quite low so a large force is required to make it move. Maximising this angle helps to reduce the force required to get it started.

Wednesday, 2 September 2009

Still waiting..but some progress

I'm still waiting for a 'rod clevis' to go on the end of my 250mm cylinder which will enable me to test the skeleton lifting mechanics. Ironically the website '' informed me they no longer stocked such an item 2 weeks after I ordered it.

Whilst waiting I designed the PCB for the parallel port interface. Here it is:

I originally intended to manufacture it myself but I found someone to make it for me in China for £46 delivered. Bargain!

Tuesday, 25 August 2009

I made a mounting plate and piston rod end hinge for the piston I'm going to open the coffin lid with.

My Lego lash up suggested to me that the mechanics were sound, but I made a full size version up to test the theory:

Here's a video of it in action, I was running it at quite low pressure (around 60psi) so there is plenty of room for improvement in the speed department.


Wednesday, 19 August 2009

Rats nest

I've now got all the schematic symbols sorted out and I'm ready to start designing the PCB. This basically involves placing copper tracks in place of the links between components on the PCB. I start out with the rats nest below and move/conenct
components until they are all connected as required ans sensibly positioned.

It's alive..well sort of

The small pneumatic cylinder I ordered from Ebay arrived today.

I'm going to use this to open the coffin lid. It has a 125mm stroke. As I need to make sure the mechanics will work I knocked up a simulation with some old Lego technic that has pneumatics!

Here is the lash up:

And a video of it in action. The red plate is the coffin lid!


Saturday, 15 August 2009

Revised Design

I decided that I needed to add some LEDs to show the ouput status of each channel, and some switches to allow the inputs to be stimulated.

Now to check all the component footprints before I design the PCB.

Here's the new schematic:

Thursday, 13 August 2009

Interface Design

I finished the PC parallel port schematic. Just need to double check it then I have all the fun of finding the appropriate footprints for the components I wish to use. I think I'm going to go for a combination of surface mount and through hole components as I already have through hole stock of some of the bits.

Halloween beginnings

I've decided to start blogging some of the stuff I do in my spare time. First off I want to blog the development of a new Halloween show I'm doing for the house for 2009.

Last year I put on a show involving gravestones, lightning and smoke. This year I'm going to add
a coffin with door that opens as trick or treaters approach, and maybe put a skeleton that rises out of it.

I plan to develop an interface board to allow me to detect voltages and switch relays from the PC
parallel port as this is an easy port to connect to the outside world. The mechanics will be operated with pneumatics.

I started the ball rolling last night buy starting the interface board design and ordered some 12V solenoid valves:

And a pneumatic cylinder to raise the dead with:

This has a 250mm stroke so I'm hoping that with sufficient pressure it will raise a skeleton a la Nosferatu.