Author Archive for Andy Murkin


The Binary Winder

I’d been planning a circuit which required a rapid input of binary numbers, ideally from a microprocessor, and it occurred to me that this could be a useful companion to the Bigfoot sequencer or the Chessboard Keyboard  – both methods I was using for sending binary data to keyboards and other devices.

I figured that this could be done manually by using a 16-way hex switch with no end stop – as they are commonly found – and a winding handle as used for re-stringing a guitar.

I bought a couple of these very cheaply on eBay:

and glued the switch inside the body of the string winder – the part which normally fits over the guitar machine head:

This would be the part of the device which did all the work.  Connecting +V to the common pin of the switch would enable it, as it was turned by the handle, to output the 16 binary numbers from 0000 to 1111.

The actual circuit itself was built inside one of the small transparent plastic boxes – described as ‘jewellery cases’ – which I had previously used for small projects such as the Touch-Radio and various effects devices.

In the above pictures the 16-way switch can be seen on the right-hand side, the 5-pin DIN binary output socket at the bottom, and 4 LEDs at the top to indicate the binary number.

The purpose of the 4 DPDT switches in the middle is to change the order of the 4 bits of the binary number.  This was so that winding the handle wouldn’t just produce an output running up and down the scale, but could be changed to give a bit of variety.


The actual circuitry consisted essentially of passing 9v to the 16-way switch, and the outputs of the 16-way switch to the 4-pin DIN socket via the 4 DPDT switches and a 4050 output buffer.

There was space inside the case for a 9v PP3 battery, so I included a battery clip inside, but also added a 3.5mm socket for external power.

As with many of my devices, I stuck a square of velcro on the back of the box so that a PP3 battery in a holder could be attached.

Space was a little tight inside, but not enough so to cause problems, and after some time the switches were all connected together with the 4050.  I didn’t bother with a circuit board, but just soldered all the connections to the 16-pin i.c. holder which the 4050 was plugged into.

Surprisingly, the case  closed without difficulties, and I was able to test it out with a couple of recent devices with binary inputs, The Telephone and the Carousel Keyboard.

In fact, there is a limit to how quickly these devices can respond to the winder – especially when the pitch is lowered, which seems to slow down the instruments’ responses as well.  However, it was very effective indeed in creating an instant sequence more quickly and accurately than it could be played on a keyboard – especially a keyboard with tiny keys like the Carousel.


The Carousel Keyboard

‘Carousel’ was just the brand name of this toy keyboard, it didn’t unfortunately look like a carousel . . .

. . . but having just finished the Animal Band and The Telephone, I wanted, while it was in my mind, to work on another device that could be controlled by the Bigfoot, only this time with a full two octave span, the ability to play a variety of different scales, and be tuned to play these scales in any key.

I opened up the Carousel, and it looked as though it would fit the bill.  The chip on which it was based was securely hidden under a black blob, but there were sufficient additional components to make me think a few simple hacks would be possible.

First of all, I wanted to check the instrument’s ability to be tuned.  I inserted batteries, switched on and began testing the circuit using the traditional wetted finger method – that is, starting the instrument playing one of its demo tunes and applying a wetted fingertip to different resistors on the board.

After a short test, I found the resistor that controlled the instrument’s pitch and timing.  It was a tiny SMD (surface-mounted) component, just 3 or 4 millimetres long, so was easily – though carefully – removed.  Its value – again, printed on the circuit board – was 300k, so after it was removed I replaced it with a 1M potentiometer, to increase the range of notes the instrument could produce.  The spot from which the resistor was taken is arrowed on this photograph, and the two leads going to the potentiometer can be seen:

(Also visible in the background are the wires connected to the PCB tracks required to trigger the notes).

I experimented with the resistance and found that the minimum the device would accept without crashing was about 200k, so I added an extra couple of 100k resistors before the 1M potentiometer, and found that a considerable variation in the pitch was achievable.


Early on in this process I disconnected the internal speaker, which was quite terrible, and added my standard 4mm banana sockets for attaching an external speaker.  The sound was 100% improved, and experimenting became a great deal more pleasurable.

Just beneath the speaker sockets a switch can be seen, which I connected up to allow the internal speaker to be selected, if an external speaker wasn’t available.

I later added an audio out socket, to allow the Carousel Keyboard to be played through the Taurus amplifier.  At first this didn’t work at all – virtually no sound came out, even though it would work with the internal or external speakers.  But I realised the output of the circuit needed a load in place of the speaker, so I put a 10 ohm resistor between the audio out and ground pins on the audio out socket, and after that it worked fine with an external amplifier.


I was saved from having to do the job I had performed on the Animal Band and The Telephone, working out which PCB tracks needed to be connected to produce the different notes: to my surprise, this was printed on the back of the circuit board.

There appeared to be an 8 x 5 matrix, so connections were made to the relevant PCB tracks, ready to be brought out to a new board.


The intention was to be able to control the keyboard with the Bigfoot sequencer, so I added a 5-pin DIN socket and 4050 buffer, as usual, ready to accept the Bigfoot’s 4-bit binary input.  This is in the form A B C D, where A is the last – rightmost – bit in the binary number, and D is the leftmost.  A is sometimes referred to as the LSB (Least Significant Bit) and D the MSB (Most Significant Bit).

The binary number 0010, for example (the number 2) would mean that D was 0, C was 0, B was 1 and A was 0; in practical terms this means that input D was 0v, C was 0v, B was +v and A was 0v.

I needed one of the inputs (D) to be inverted – i.e. if the input was 0v, I needed +v, and if the input was +v, I needed 0v – so with the 4050 was a 40106 inverter, with sections which change 0v to +v and +v to 0v.  There was very little space inside the keyboard case, so the board with the 4050 and 40106 was tucked under the output socket.  (This was before I added the 10 ohm resistor on the socket).

The circuit of the input section was like this:

There are 6 buffers in the 4050 chip; 4 of these are used (marked A B C D) and the inputs of the other two are connected to ground.  Likewise, there are 6 inverters in the 40106; 1 of these is used and the inputs of the other 5 are connected to ground.  Unused inputs on CMOS chips should normally be grounded like this to ensure correct operation.

Normally, I would use a 4067 to cover the two octaves produced by the Bigfoot – as in the Animal Band and The Telephone – but in this case that wouldn’t work.  The 4067 is essentially a 16-way switch with a single pole; in this case there were 4 different ‘poles’ to which connections needed to be made, since the notes are produced by a matrix.

Using four 4067’s would be perfectly possible, but unnecessarily expensive – each one costs between 30 and 50p, and is physically quite large, being in 24 pin wide format.  As there would only be 4 or 5 connections to each pole, it would be more effective in terms of cost and space in this circuit to use 4051’s.  The 4051 is an 8 pole switch which works in more or less exactly the same way as the 4067, but is physically smaller  – and costs less than 15p!

An important difference between the 4051 and the 4067 – related to the number of outputs – is that the 4067 requires a 4-bit binary input (16 numbers, from 0000 to 1111), but the 4051 only a 3-bit (8 numbers from 000 to 111).  This means that a different way must be found with the 4051’s to ensure that outputs for the first 8 numbers are separate from the outputs for the second 8 numbers.

This can be done by using the Enable/Inhibit pins of the 4051’s.  Each 4051 – just like the 4067, in fact – has an Enable/Inhibit pin: if this pin is at 0v, the chip will work, and convert its binary inputs into individual outputs; if the pin is at +v, it won’t work.

So, the first 3 inputs from the Bigfoot binary input socket, A B & C, are passed on to the 4051’s in the next part of the circuit, but the 4th input, D, is not.  Instead, the 4th digit is used to turn pairs of the 4051’s off and on via their Enable/Inhibit pins.

4051’s 1 & 2 output the lower 8 numbers (0000 to 0111), so as long as the 4th, leftmost, digit is ‘0’, these two 4051’s are enabled.  0v at the Enable/Inhibit pin achieves this.

4051’s 3 & 4 output the higher 8 numbers (1000 to 1111), so if the 4th digit is ‘1’, an inverted signal from the 40106 sends 0v to enable these two.

The circuit to convert the binary input to separate outputs looks like this. (The 40106 gate is repeated from the diagram of the input circuit):

The lower 8 notes are divided between the top two 4051’s in the diagram, which work together with no overlap in notes, and the higher 8 notes are divided similarly between the bottom two, according to which common pin they must connect to.  The pin connections are named in the diagram as they appear printed on the keyboard’s main PCB: the 4 common pins are connected to tracks named BP10, BP11, BP12 and BP13.

The reason there are many more than 16 output pins shown is connected with the principle of the Bigfoot sequencer.  The idea is that the sequencer outputs the notes of a scale – do, re, mi, fa, so, la, ti, do – but the exact scale – major, minor, melodic, harmonic, etc. – is determined by switches on the receiving instrument.  Normally there would be 5 double pole switches, but due to the configuration of the pins in the Carousel keyboard, one of the switches (SW2) needs to have 3 poles.


As with other of my designs like this, there wasn’t a lot of circuitry as such – just a lot of interconnection between the chips.  After soldering the dozens of wires needed to link the 4051’s with the switches and the Carousel keyboard’s PCB, the inside of the instrument looked like this:

There was just enough room for the new circuit board with the four 4051’s on it.

The Chessboard Keyboard proved very useful in checking that everything was working properly – one wrong note revealed a connection error on one of the switches! – and the 4 LEDs were a good double check that the binary input was being interpreted correctly.


Although the pitch control potentiometer worked well, I decided there was a need to be more precise about the pitch, which would effectively set the key the instrument would be playing in when controlled by Bigfoot.  So, as I had done earlier with The Telephone  – referred to above – I added a switch to change between the potentiometer and a 12-way switch.

Between each of the output pins of the switch, I inserted a 100k trimmer – with an extra 100k trimmer before pin 1 – so that the pitch of the instrument could be set to any one of the 12 steps in the octave.

In The Telephone I used ordinary single-turn trimmers, but I though it would be a good test to see if multi-turn trimmers would be as good – that is, as accurate in establishing the pitch, remaining in pitch, and not taking up too much space in the cramped enclosure.

The type I chose looked like this:

Buying 20 at a time enabled me to get them at a reasonable price – about 8p each, although this was probably twice as much the single-turn trimmers I had used in The Telephone.  They were also much more than twice as big.

However, I soldered them all in place and set about adjusting the pitches.

In this instance, I didn’t really find a big advantage in using the multi-turn trimmers.  I was tuning the pitches by ear – maybe I was able to be more accurate than with the single-turn trimmers, maybe not.  It took longer to tune each note, of course, because of the number of extra turns required.

I would have been glad if the potentiometer/trimmer arrangement had been a bit smaller, but I found space on the right-hand side of the keyboard to fit it in with the potentiometer and the other switch.  This picture shows 1 – the 12-way switch with trimmers, 2- the 1M potentiometer, and 3 – the SPDT switch which allows either the 12-way switch or the potentiometer to be selected.

I chose two knobs which fitted the space available on the top surface, drilled holes and fixed them in place.


That was everything I planned to do with the Carousel keyboard for now, so I carefully closed up the case and screwed it back together.  I had to cut some rectangular holes in the base to make room for the 5 switches, but surprisingly everything else fitted in.



The MIDI CPU Project – 3. Bass Pedals

After building the MIDI CPU box and programming it to accept input from keys, switches and potentiometers, it was necessary to build MIDI instruments to use its features.

As the MIDI CPU accepted input via a 25-way DIN socket, it would just be necessary to equip each instrument with such a socket and link it to the MIDI CPU with a suitable cable.

The first instrument I’d planned was a set of 13-note bass pedals, and the initial SysEx file with which I’d programmed the MIDI CPU was suitable for this application, with the first 13 control terminals, 0 – 12, configured as a complete octave from C0 to C1.

I got the pedals from a local seller on eBay who dismantled and repaired Hammond organs.

They were in excellent condition, and the switches on each of the pedals seemed to be still wired.  They looked like this:

and the actual connections were like this:

Pedal switches

The two tabs on the front linked one side of all the switches together; when a pedal was pressed, this bus would be connected to the other side of that individual switch, the tab on the top.  This was perfect for this application, in which an individual switch connected to 0v would be interpreted by the MIDI CPU as a note command.

My main task, then, was to connect each of the 13 switches to a 25-way socket, in order to pass the switch presses to the MIDI CPU box.

In addition to this, I wanted to have Octave Up and Down and Hold commands available, so there would be 3 further connections to the 25-way socket.

Finally, I would have to construct a housing in which the pedal unit would sit.


There were no circuits as such involved in this project – it was just a case of wiring up the switches and connecting them to the socket.  At the same time I decided to add a couple of extra sockets that would enable the pedals to be used in a different way if necessary.

The additional sockets added were a 15-way socket, which would be compatible with the Superstylonanophone (another MIDI device, with  a built-in MIDI-USB interface):

and a 9-way socket compatible with the Apple IR remote:


I connected the switches to the sockets and, because the enclosure I had planned was designed to have another instrument on top of it (another MIDI foot controller, a Digikick Footar) I connected the Hold and Octave Up and Down connections to 1/4″ sockets so these switches could be external, rather than on the top of the pedals.  All the sockets were housed in a small panel, which would be attached to the rear of the enclosure.


After connecting the switches to the sockets, I found a D25 cable and attached the Bass pedal unit to the MIDI CPU box.  At the moment the MIDI CPU box is connected to a laptop via a Midisport 2×2 MIDI-USB interface – along with the Digikick Footar – and controls software instruments in Apple Logic.

I added 2 or 3 different bass instruments to the Logic set-up and tested the pedals.  All notes worked as they should.

With an external switch I tested the ‘HOLD’, ‘OCTAVE UP’ and ‘OCTAVE DOWN’ functions, which seemed to be working OK, so deemed it safe to screw down the top of the case in which the pedals were housed and fix the panel to the back of the case.


The Animal Band & The Telephone – 2

This post actually concerns The Telephone, to which I decided to make a small further adjustment.

After finishing the Animal Band and The Telephone, I realised it would be a bit limiting to leave them playing in only one key, so I went back to The Telephone and searched for the resistor which controlled the pitch of the notes.

Having found it – by means of the tried-and-tested wetted finger method – I removed it from the circuit board and replaced  the connection with a pair of wires.

In the past I had replaced such a resistor with a potentiometer, enabling continuous – and wide-ranging – adjustment of pitch.  In this instance, however, I just wanted to be able to tune The Telephone to other keys, so instead of a potentiometer I added a 12-way rotary switch, the idea being to tune each step precisely to each key.

The Telephone was in the key of B – B being the lowest note it would play.  Rather than make this the lowest key and have all the others higher, I thought it would be better to have B in the middle, with some of the others lower, and some higher.

After some experimentation, I concluded that the difference in resistance between one note and another was just a few k.  I had a number of spare 10k trimmers, so decided that these could be used.

I connected one of these between each of the 12 pins on the switch.  The last one was connected to the circuit board on one side of where the original 100k timing resistor had been; the pole of the switch was connected to the other side, via a 100k trimmer to bring the resistance roughly into line with the original.  In this way, when the switch was at position 1, it would connect through the 100k trimmer and the first of the 10k trimmers; at position 2 the value of the second 10k trimmer would be added; at position 3 the value of the second and the third would be added, and so on to the end.  The way it worked, the more resistance, the lower the pitch.

In the end, I couldn’t reduce the resistance enough to have B right in the middle – the device wouldn’t operate at the highest frequency required for that – so it ended up in 4th position on the switch.  It was quite OK to go down another 8 semitones so that any key could be selected while The Telephone was being operated by the Bigfoot sequencer.

I found a suitable knob to go on the switch, and put The Telephone back together.  Enabling it to be used in any key would make it a much more versatile addition to the collection.


The Alien Choir

The Alien Choir wasn’t a device I particularly wanted to circuit bend- the alien voices it makes are fine as they are!  – but I wanted to do a couple of things to make is easier and better to use.

The Alien Choir is one of the ‘Finger Beats’ series.  These are recognisable by their distinctive design, and are all operated in a similar way, using light finger pressure in certain places on a colourful illustration on the front.

I don’t have an instruction book with mine, so it’s not clear that all of its functions are working – in particular, recording samples with the built-in microphone – but it makes 8 excellent alien voice sounds.  The volume of the sounds can be turned up or down with the ‘+’ and ‘-‘ buttons on the left-hand side.


First of all, although 3v isn’t an odd or unusual value, I decided to add a socket and dc converter to allow the device to be powered by a mains adapter or larger – e.g. 9v – battery.  To this end I also added a small square of velcro to the back, as I had with other instruments before, to allow one of my 9v battery holders to be attached.

The dc converter was a small and inexpensive (less than 50p) module, which didn’t need any additional components, just an input voltage from 20v down to about 1v higher than the desired output voltage.  The output voltage is set by means of a small trimmer on the board.

In this case I found that the required voltage, as measured on my multimeter, needed to be a little lower (about half a volt lower, in fact) than the anticipated 3v in order for the circuit to work smoothly.  I don’t know if this is something specific to the Alien Choir, a difficulty in measuring the voltage precisely, or what.

Inside the device, I added a switch to choose between the battery or the external socket.  In the following picture  1 indicates the socket, 2 the dc converter and 3 the switch.

The device has a 3.5mm audio out socket (and an audio in, in fact, as can be seen in the lower right-hand corner of the picture above), but I decided to add banana sockets for connection to one of my external speakers.  This always produces a much better sound than the small built-in speakers these devices are fitted with.

The small switch on the right selects either the internal or external speaker.

I hope this will be a useful – and certainly attractive – addition to the ‘Outer Space’ section of my instrument collection.


The Animal Band & The Telephone

This project came about as I was looking through my collection of electronic toys for additional devices that could be controlled by the Bigfoot sequencer or the Chessboard keyboard.

I don’t know if ‘Animal Band’ and ‘Telephone’ are the correct names for these toys, but they are sufficiently descriptive to identify them amongst my various devices.

Both the Bigfoot and the Chessboard encode the 15 pitches (2 octaves) they can produce into 4-bit binary numbers so that they can use standard 5-pin DIN connecting leads – the same as MIDI leads – rather than more complex multi-way connectors to control sound-making instruments.

I came across two devices, which were rather limited in that they played only a one octave scale; but it was the same scale – B major – and one of them had not only small animal musicians who moved as the notes were sounded, but was also capable of playing a scale with various animal noises.  For some reason, this scale turned out to be A major, but this was only a minor inconvenience.

The additional electronics required would be similar to those in The StyloSound, the main thing being a circuit to convert the binary number input from the Bigfoot or The Chessboard to the individual notes of the scale.  Both the devices would need one of these.

The basic circuit I use looks like this:

Receive circuit 3

At the beginning, the input passes through a non-inverting buffer.  (There are 6 connections from the input to the buffer in case a later plan for operation via MIDI is implemented, which is designed to use 6 bits.  For the time being, only the first 4 are being used, the other 2 remaining unconnected).

The purpose of the buffer is to reduce the incoming signal level (which, from both the Bigfoot and the Chessboard, is at 9v) to 4.5v, the voltage of the Animal Band.  The 4050, unusually, is able to deal with an input signal which is higher than its supply voltage, which makes it ideal for this purpose.

When functioning, the 4067 will interpret the 4-bit binary input on pins 11, 12, 13 and 14 as a decimal number from 0 (0000) to 15 (1111) and act as a switch, connecting pin 1, the Common, to one of its 16 outputs on pins 2-9 and 16-23.  Each of the 4 binary inputs is held at 0v by 100k resistors, interpreted as a ‘0’ by the 4067, so a +v pulse on one or more of the inputs pulls them high, acting as a ‘1’

To avoid silences – Bigfoot produces 16 notes, the Animal Band produces only 8 – the output pins for notes 9 – 15 are connected to the pins for notes 2 – 8.

Pin 15 is brought out to an SPDT switch.  When connected to +v, the 4067 is turned off; when connected to 0v, it is turned on.  The Telephone would have a similar switch.  In this way either instrument can be set to work or not work without disconnecting the power.


To find exactly where to connect the Common and output pins of the 4067 I needed to search inside and test different points on the printed circuit board.

I removed the top:

Animal Band top

and examined the inside:

Animal Band inside marked

The important sections are marked.  (Normally the LEDs are pointing upwards, but I was in the process of examining them when I took this picture and had unscrewed the circuit board on which they are mounted).  In the centre of the device you can also see the rod by which the stepper motor moves the figures of the animal band when notes are sounded, and at the bottom the actuators which are pressed by the keys.

The first thing I did after opening the case was to give the actuators a clean.  They are the typical type – like computer keyboards or game controllers – which, when pressed, connect together two narrow tracks on the PCB.  If dust and dirt get inside them, they can operate erratically.

This is a typical example (from The Telephone) of the PCB tracks underneath a button:

Button pad

Apart from cleaning these small PCB tracks, I gave the carbon or graphite blocks which make the connection a light scrape to make sure their surfaces were also free of dirt and dust.

The important connections inside the Animal Band seemed to be grouped together in the bottom left-hand corner, so these are the connections I looked at first.  After testing them, I could see that the following connections needed to be made:

Animal Band PCB

The point marked ‘Common’ needed to be connected to pin 1 of the 4067, and the 8 notes to first 8 output connections on the 4067.  (Actually, output 1, pin 8, in the Bigfoot system is not connected, so the unit is silent on receipt of 0000.  The first note sounded is 0001, so the outputs used are 2-9, starting with pin 7).

In the Bigfoot system, an instrument which can sound all 12 notes  in an octave would have switches to raise or lower some notes of the scale (the 2nd, 3rd, 4th, 6th and 7th notes), but the Animal Band and the Telephone are fixed to play a major scale, so these switches aren’t needed.


Finally, there needed to be a circuit to connect the Animal Band and The Telephone.  This would have to combine the input from Bigfoot, the Chessboard (or other 4-bit binary input) and send this in binary form to The Telephone.

This consisted only of inputs from two DIN sockets, entering via diodes, and passing through a second 4050 buffer.

The circuit board ended up looking like this, as I had originally planned to include a further circuit which would convert 16 individual inputs to a 4-bit binary output (as used in the Chessboard):


The large 24 pin chip at the bottom left is the 4067; the two chips above are the input and output 4050 buffers; the other 3 chips are two 4532’s and a 4071 for the unused binary-converting ‘Send’ circuit.  The diodes in the bottom right are for the inputs from Bigfoot and the Chessboard.

The board was designed to fit into the rear section of the Animal Band, behind the ‘organ pipe’ section with the LEDs in it.  I added 6 extra LEDs here, connected to the 6 outputs of the 4050 input buffer.

Most of the connections – including the 6 new LEDs – can be seen in this view of the inside, just before putting the case back together.


This picture shows 3 of the new sockets and switches.  1 = the 5-pin DIN Out socket; 2 = the 4067 Enable/Inhibit switch; 3 = the audio out socket.  When a 3.5mm plug is inserted into the socket, the speaker connection is cut out.



The Telephone needed a similar circuit.  The 4067 is one of my favourite chips, and I’ve been using it for some years, but recently, it seems , the Arduino hobbyists have started to use it, as there is now a reasonably-priced breakout board available, using an SMD version of the chip.  This looked like a real time-saver for me, so I bought a stack of them – at a cost of about 70p each – and The Telephone was my first chance to use one.

4067-Breakout-BoardAs can be seen, the 16 outputs are brought out on the left-hand side of the board, and on the right-hand side are ‘SIG’, which is the Common output on pin 1; the 4 binary inputs S0-S3; ‘EN’, the Enable or Inhibit pin; +v and Ground.

I couldn’t use this breakout board in every situation: the information with it said the maximum voltage should be no more than 7v – elsewhere I have even seen 6v.  I think the intention is that it would be used with 5v, like the Arduino, but in any event the 4.5v I was planning to use with the Animal Band and Telephone would be well within the limits.

Inside, The Telephone looked like this:

Telephone inside

The main circuit board inside The Telephone sits under the 12 buttons of the keypad.  It looked as though the important connections were down the right-hand side of the board, so, tracing the tracks, it was possible work out which ones needed to be connected to produce each of the notes The Telephone was capable of.

Track 8 was the ‘Common’.  This track needed to be connected to one of 8 of the other tracks to produce the notes of the scale.  I identified which 8 tracks these were and connected these, plus the Common, to the 4067.  As with the Animal Band I connected outputs 9 – 15 to outputs 2 -8 to make sure The Telephone would be constantly sounding – except when in receipt of a 0000 input.

According to the circuit diagram of the module, it appeared that the Inhibit or Enable pin  was tied to Ground with a 10k resistor, so the unit would automatically be working when the power was switched on. 4067 breakout board schematicThis meant that only a SPST switch would be required to connect the pin to +v if it was necessary to stop it functioning.

The telephone was a less complicated unit than the Animal Band, so I just needed to connect the 4067 module to the input via a 4050 buffer, for which I just used a 16-pin i.c. socket, rather than a piece of veroboard:

Also visible in this picture are the four 100k resistors connecting the inputs of the 4050 to ground, and the audio out socket, which cuts out the internal speaker when a 3.5mm mono plug is inserted.

The outputs of the module were connected to the appropriate points on the Telephone PCB:

The only other thing to add was a switch attached to the enable/inhibit pin of the 4067 to allow the unit to be switched off without removing the power.  As mentioned above, the enable/inhibit was attached to ground internally in the module, so the switch just required a connection to +v, which would stop the 4067 from functioning.

This switch can be seen on the front left of this view of the outside of the finished unit:

On the rear can be seen the audio out (top) and 5-pin DIN (bottom) which can accept input from the Bigfoot sequencer, or a device compatible with the Bigfoot 4-bit binary note system (e.g. the Chessboard keyboard).


Having reassembled everything, it was time to check the devices in operation with the Bigfoot and the Chessboard, plugging them together with standard 5-pin DIN (or MIDI) cables, like this:

Everything seemed to work as expected, and the two units played in unison – or individually if one or other of the enable/inhibit switches were turned off – when operated either by the Bigfoot or the Chessboard.

Click here for a short film of the set-up taken on my iPhone.



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:

Chessboard keys 5a

‘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].

Chessboard top

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.

Chessboard keys 5b

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.

Chessboard LEDs

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.

Chessboard Closed

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.

Chessboard inside


October 2017
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