First, you need a mock-up of the handlink made out of coloured translucent plastic. Or anything you can get your hands on. The important thing is that it looks a bit like the real handlink, you can put lights underneath the coloured blocks to light them up, and that you can hide buttons under a few of them. Actually that last one's not essential if you don't mind having buttons that are not hidden. Anyway, this is the most difficult part. If anyone can suggest suitable building materials you are welcome to mail me so that I can mention them on this page. My current idea is to use unfolded soft-drink bottles (these come in a few different colours, for instance 7-Up and Lilt come in green bottles and Tizer comes in red bottles) or the white translucent plastic used in certain milk cartons. These can be painted, or coloured with overhead-projector pens (there are also such things as overhead-projector highlighters which include yellow and pink colours). There is also of course Lego, but while that would be easier to build I think it would be much harder to light up convincingly.
It will obviously be necessary to know what the handlink looks like. I have drawn an `artist's impression' (well OK then, just an `impression') of approximately how the handlink looks. There is a mini version of it at the top of this page.
I have scanned in a circuit diagram of my handlink. I rubbed out all my handwritten numbers and words and typed new ones. By the time I finished that I suppose I could have redrawn the whole thing, but I didn't so what you get is an ugly drawing with readable text on it. For best results, print out this huge GIF image (85K; 2165x1365 pixels in black-on-white) at about 200 dots per inch, or slightly more if it doesn't fit on the paper. You could also try this half-size GIF (53K; 1083x683 pixels in black, white and grey) which might fit on your screen if you have a good enough display. You might find it a bit difficult to read.
The parts list is as follows.
| DIL switch SPST x 8 (S8 unused)
| DIL switch SPST x 4
| miniature push-to-make switch
| push-on-push-off SPST switch
| 16 ohm loudspeaker (see text below)
| miniature electret microphone
| 3.5mm jack socket for audio input
| standard LEDs of varying colours
| high-brightness LED
| 4K7 potentiometer or preset
| 560 ohm (or 390 ohm for blue LEDs with 3V forward
The circuit is moderately large and surprisingly expensive to build. I daresay a cheaper one could easily be designed. This one, however, is designed to flash lights in a non-obvious pattern rather than in repeating cycles. A brief description of the circuit elements follows.
IC10 is a very low power voltage regulator which converts your 9 volt battery into a 5 volt power supply. This is needed chiefly for the sound chip, IC1, but in fact it is used to power all the logic and the lights - which occupy the right-hand section of the main circuit. The little circuit in the middle involving R5, R6, C9 and C10 is an oscillator which cycles about five times per second and provides the main driving signal for the flashing lights (actually the real one flashes rather faster than this - decrease the values of the components to speed it up). ICs 4, 5 and 6 are counters which input the signal from the oscillator and alternate it around their outputs in cycles of 9, 10 and 8 respectively. This means that at any one time there will be three LEDs lit, and the pattern of flashing LEDs repeats every 360 flashes (the lowest common multiple of 8, 9 and 10). The 27 signals are reduced to 18 by connecting some of them to the same LEDs - this means that some LEDs flash two times per cycle instead of once, giving an additional `random' appearance. ICs 7, 8 and 9 are drivers; the signals from the counters are not (in theory) strong enough to light LEDs by themselves so they are passed through buffers before going to the LEDs. R30-47 are current limiting resistors which save both the buffer ICs and the LEDs from burning themselves out.
IC1 is a sound chip made by ISD. It has the capability to record sounds and play them back. The sounds remain in memory even when there is no power to the IC. I have configured the IC to store nine sounds: four `pops', four `squeaks' and one soundbite. The soundbite is 3.2 seconds long while the other sounds are 1.6 seconds long. In normal operation, the handlink chooses a sound at `random' depending on whether you press the `pop' or `squeak' button, or you can press the soundbite button to play the soundbite. In order to save space on the circuit board I put the components necessary only for recording the sounds on to another small circuit board which plugs into the main circuit board by means of the eleven terminals (T1-11).
The loudspeaker is a difficult component. Usually only 8 or 64 ohm ones are available (the best thing is to use an 8 ohm one in series with an 8 ohm resistor), and in any case even the miniature ones can be a bit bulky. One possible solution is to use a wafer-thin piezzo transducer, but in order for that to work you have to find an impedance-matching transformer with a primary of 16 ohms and a secondary of about 600. I tried building one of these with limited success.
So, now comes putting the thing together. I found the circuit to be rather bulky so it didn't really look right to carry the whole thing round and pretend it was a handlink. So I put the main circuit in its own box and attached a ribbon cable between the box and the plastic handlink. That way I can put the box in my pocket and feed the wire up my sleeve. When I met Mike Tucker (a special effects guy) at Accelerate 96 he told me he'd been wondering where on earth the power supply was until I pulled the box out of my pocket. I've inserted some plugs into the ribbon cable so that I can attach the handlink more or less directly to the box if I don't feel like wiring myself up.
I think that it is probably possible to build the circuit in such a way that it is small enough to attach directly to the handlink. For this you will probably need to use surface-mount technology and a double-sided circuit board. I'm not about to try it, but when I have lots of money and time to spare . . .
So anyway, for the separate box and handlink approach you will need a separate circuit board to attach all the lights and switches to and then bolt it to your mock-up of the handlink so that the lights shine through the coloured blocks, and you can press some of the coloured blocks and make things happen. Note, incidentally, that blue LEDs are slightly dimmer and very expensive compared to the other colours, so you will probably want to slip green ones in instead. If you do use blue LEDs, you can change the limiting resistors connected to those LEDs from 560 to 390 ohms, because the blue ones have a higher voltage across them.
You will obviously want to position the lights carefully under the blocks so
that they light the blocks up. In my handlink I also hid buttons under the
blocks so that you can't tell they are there. The diagram you see here is
an outline drawing (of the older design) showing
the positions of my buttons; I have coloured in
the blocks which have buttons in them. The orange one at the bottom is the
on-off switch (S17). You press it to turn the handlink on, and press it
again to turn the handlink off. The red and green ones nearby are
The red one is the `pop' button and the green one is the
`soundbite' button. For example, I can open the chamber door by pressing
the green button. The yellow one in the corner hides the `squeak' button.
The button is positioned edge-on so that a good slap on the side of the
handlink will activate the sound.
So, finally, here are the instructions on how to record some sounds on the handlink. With the recording circuit plugged in, of course.