The Chessboard Keyboard

The purpose of The Chessboard was two-fold: firstly, to continue my experiments with alternative keyboards, and secondly to use the ability of the Bigfoot to control a Stylophone (or other sound-producing devices, but so far the only ones I have which are adapted for this purpose are the SoftPot Stylophone and the StyloSound) by means of binary input.

The idea for the Chessboard was that it would have 64 keys, one for each of the black and white squares.  These would not be arranged according to the Janko, Wicki-Hayden or other alternative keyboard layout, as the principle of the Bigfoot is not to provide all the notes in the octave, but just the notes in a particular scale.  So the 64 keys would cover 15 notes over 2 octaves, like the sequencers in the Bigfoot, and note information would be passed to Bigfoot in 4-bit binary form.

I managed to get 64 buttons – tactile switches – for  a few pence each, and glued one to each square on the board.  One side of each button was connected to +V, and diagonal rows of buttons were connected in parallel to produce a pattern of notes in the 2 octave scale, like this:

‘1’ means ‘root note’, ‘2’ means 2nd interval, ‘3’ means 3rd interval, etc.  Switches on the Bigfoot determine whether the intervals 2nd, 3rd, 5th, 6th and 7th are major or minor (natural, or lowered by a semitone).  [Note 8 is an octave above the root, note 15 is two octaves above; the 9th, 10th, 12th, 13th and 14th intervals follow the 2nd, 3rd, 5th, 6th and 7th ; the 4th and 11th are not changeable].

The circuitry to encode the 15 individual notes into binary form was exactly the same as I had recently used in the StyloSound, utilising two 4532 chips and a 4071.  The four binary outputs were buffered by a 4050 before being sent to a 5-pin DIN output socket.

LEDs were wired to the  A B C D outputs, to give a visual indication of the binary signal being sent out.  This was also helpful as work progressed in checking the correctness of the output and the smooth operation of each of the 64 buttons.

In fact, I added them into the circuit between the 4532s/4071 and the 4050.  This was an old design from a few years ago, which I’d just got round to finishing: if I was to redesign it now I’d put in a duplicate 4050 – one for the LEDs, one for the output, just to make sure the circuit would operate reliably.  I’ll keep an eye on it and make sure I get the output I’m expecting at all times.

As can be seen from the photographs, the particular chessboard I used was a small travelling set, which would normally be folded in half, with the pieces kept safe inside.   I arranged it so the board could still be folded and the circuitry – including the battery and the inline DIN socket – retained within.  In the end I replaced the battery with a 3.5mm socket – in common with many of my instruments – as this was a more versatile method of powering the circuit.

The only problem remaining at the end was that the circuit board was not quite thin enough to enable the board to be opened up and laid flat to be played, so some inserts need to be added to raise the base a little higher.  I’ll add a picture when I’ve worked out the best way to do this.