Poltergeist : From the German for “noisy ghost”.
A metaphysical entity which announces its presence with rapping, banging and general mischief making.
It wasn’t easy, but I’ve got one shut up in this box. I call him Piecax. Sometimes he will lie quietly and make you think he’s gone, then startle you with frenzied knocking. Other times Piecax will have fun by echoing you. Find his favourite number and he might play you a spooky tune. Watch the video to see Piecax in action.
Thanks and credit go to JKestner whose Knock Block gave me the inspiration for this project.
Step 1: The Box
I did this first so I wouldn’t be waiting for varnish to dry once I’d built the circuitry.
I started with a cheap softwood box from a craft shop. I clamped a rotary sander upside-down in a vice and rounded the corners and smoothed the sides, starting with a coarse sanding sheet and finishing off with fine. A final rub over with very fine paper and I had a smooth rounded box but a bit of a boring colour.
To bring out the grain I gave it two coats of walnut woodstain and then for the gloss, three coats of yacht varnish. The first coat was diluted with thinners to make it soak into the wood and give it more hardness and a good base for the other coats.
A quick raid on my sons' lego sets and I had a casket fit for a ghost.
Step 2: The Electronics
* I'll re-write when I get a chance. *
Step 3: The Mechanics
The various parts are stuck on with contact adhesive (that’s the type where you apply a thin coat to both surfaces, wait a few minutes, then it sticks hard immediately you put the parts together.) The sounder is glued to the lid so it picks up the vibrations directly as the top is tapped.
For the ‘knocker’ I used a small 3V DC motor with a piece of brass strip bent fixed to the shaft. I bent this to shape with a pair of pliers so it was a push-fit onto the shaft. Be careful as you push it on as the plastic back of the motor is likely to push out, so put a hard object on the end and push against that.
The motor came with a solar cell kit and had the plastic clip with it. Alternatively you could use a piece of split overflow pipe with one side sanded down, or use double-sided sticky foam to attach the motor to the box. Later on, I added solder to the end to give a good solid knock. A bit of trial and error is required to give the best weight.
Step 4: Putting the Ghost in the Box.
With the box size I used, everything goes in pretty easily and neatly. You will need to adapt the layout if you use a different size or shape of box.
The battery is held in with double-sided sticky foam so it can be replaced. The circuit board in held in the same way, and has to go in before the motor if you're using a small box.
Gluing a small piece of brass strip to the lid where the knocker hits gives a sharper knock and helps the knocker to return quickly. The final picture shows a piece of foam glued in to dampen the 'clunk' when the arm returns.
Click HERE for information about the standard training video for containment of supernatural beings.
Step 5: The PicAxe and Code
The code is here as a PicAxe .BAS file and as a Word document. There are loads of comments throughout to explain what's going on in the program. It uses 252 memory bytes of the 256 available.
20 knocks will give a 30 second sleep and then a series of 50 rapid random knocks; Long enough to put the box down in front of someone and tell them the spooky story of what it contains before it bursts into life.
13 knocks will play a tune which strikes fear and horror into the hearts of many - the 'Adams Family' theme tune.
I've used a PicAxe 08M microcontroller which comes as a blank chip and needs to be programmed. To do this, you will need a programming lead and the free programming editor software. Both the PicAxe chip and the lead are available from Tech Supplies in the UK or see HERE for other countries.
Once you have the lead, you only need a PicAxe, two resistors and whatever sensors and output devices you choose to have a full PicAxe development kit which can program any of the PicAxe range, so you can design your own projects.
The PicAxe was initially developed for the educational market in UK schools but is being widely used by hobbyists. The PicAxe is based on various PICs but with bootstrap code to interpret the downloaded programs and handle the programming side. They come in all flavours from this suprisingly powerful 8 pin package up to full blown 40 pin.
Look at the manuals and datasheets on the PicAxe site to see the full capabilities. Programming of the chip is via a serial link and done in-circuit. It takes about 20 seconds and you don't even have to unplug the lead to run the program.
I've been in electronics since the early eighties and I've never found a programming environment where the coding / simulation / proving cycle is so simple. Documentation and support from the forum is excellent and there are many robotics enthusiasts using the chips. Control for servos, steppers, ADCs etc are built in to the BASIC-like programming language as well as a host of other goodies. You can also simulate the circuit before you build, and do real-time debugging on a running controller. Look out for more PicAxe based projects from me.