Lunetta keyboard controller

PHOBoS · Last edited by PHOBoS on Sun Jan 05, 2014 4:13 am; edited 4 times in total

This is a project I'm currently working on and instead of waiting untill it's completely finished I'll post the progress I make
along the way.

It started when I went back to think about what i was gonna do with the Schrödinger II circuit. One thing that came to mind was to make
a stylophone controller for it, which then lead to the idea of using a small keyboard instead, using a cheap (€1,-) toy keyboard.

Initially I wanted to add a trimpot for each key or maybe a resistor string, but it turned out that the PCB was so small it would be hard to
solder anything to. So I ditched that idea and played around using the output of the keyboard to control another oscillator, and this gave me
the idea to just square up the output and use it as a tuned oscillator.

first a little more info about the keyboard I'm using. It has 10 keys, tuned to major intervals (white keys). When you press a key a tone will
only play for a certain duration so it stops even when the key is still pressed down. It also has a switch that puts it into melody mode.
In this mode each key plays a different melody, restarting from the first note everytime you press a key. It runs on 2AA batteries and has
a small speaker.

So now to square up the output. Well this turned out to be a lot easier then I could have hoped for because when I connected my scope to the
output a nice squarewave allready appeared Laughing

Since the keyboard runs on 3V, the output voltage isn't high enough to control anything
directly. However, as it turns out, it's an open collector output (there is no extra transistor on the PCB though), with the speaker connected
between +3V and the output. So all that's needed was a pullup resistor, connected to the voltage I want to use, instead of the speaker.
Followed by an inverting buffer for which i used a 40106. For the sound itself it doesn't have to be inverted but when there is no sound
I like the output to be low.

of course I couldn't just leave it at that. So I'm also adding remote inputs for every key (Lunetta controlled keyboard for nice sequences),
a Gate output which is high as long as a key is pressed, and a Trigger output which gives a short pulse everytime a key is pressed even
when another key is still held down. And some indicator LED's for every key.

of course I couldn't just leave it at that. So I'm also adding a simple AD/AR generator to control a very simple transistor VCA, a 4040
divider and a switch to select different octaves, which is also used to add suboctave and modulation to the sound. And a potentiometer to
control the pitch, which also affects the note length.

And I hope I can leave it at that. Cool

To be able to do all this I did have to solder wires to the PCB afterall, so I used some thin enameled wires and soldered them to a piece of perf
with a printconnector on it. This will make it easy to solder wires to it later. I also added a 3V supply using an LM317L.

I'm currently soldering the main PCB, So more info later.
But here are some photo's.

lunkeyboard01.jpg

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This is it!

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lunkeyboard02.jpg

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soldering small wires, lighter for reference

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lunkeyboard03.jpg

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connector, 3V supply and pitch pot. installed

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PHOBoS · Posted: Sat Feb 23, 2013 6:00 pm Post subject:

soldering,...

lunkeyboard05.jpg

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main PCB, under construction

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lunkeyboard06.jpg

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some more components added

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lunkeyboard07.jpg

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just a couple of transistors and a big capacitor left, but that'll have to wait untill tomorrow.

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PHOBoS · Posted: Sun Feb 24, 2013 4:22 am Post subject:

I'm done with soldering the main PCB, but before I can wire it up I first need to design a frontpanel and make a case for it and then order some
switches which should arrive tuesday. Maybe I'll solder a couple of wires to the PCB and do a couple of tests though.

lunkeyboard08.jpg

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Main PCB done

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PHOBoS · Posted: Sun Feb 24, 2013 8:32 am Post subject:

front design sofar. I think I'm gonna give it a sloped, almost vertical, front panel Cool

lunakeyfrontv1.png

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Lun-a-Key front V1

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Cynosure · Posted: Sun Feb 24, 2013 12:14 pm Post subject:

Very cool project. I can't wait for a demo Smile

PHOBoS · Posted: Sun Feb 24, 2013 1:24 pm Post subject:

Well it's a squarewave so I'm pretty sure you (of all people) know what that sounds like Wink

But the suboctave and modulation do add some extra
niceness to it. Of course controling it with a lunetta or the other way around or both, might produce some very interesting sounds. (I hope so)

Recently I cut my keyboard in half. I also cut some wood to size, but 2 parts are allready glued together, so now I'm waiting for that to dry and then I'll take a photo of it.

lunkeyboard09.jpg

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recently I cut my keyboard in half.

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PHOBoS · Posted: Sun Feb 24, 2013 3:57 pm Post subject:

not the best picture but It'll give you an idea. the piece on top is just some scrap wood (might be usefull to cover the keyboard).

and an updated cover design Cool

lunkeyboard10.jpg

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case, under construction

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lunakeyfrontv2.png

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Lun-a-Key front V2

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analog_backlash · Posted: Sun Feb 24, 2013 6:05 pm Post subject:

Fascinating as always, PHOBoS. I'm glad that the Schrödinger II had a very minor role (a very, very, very minor role Laughing

) in the chain of events leading to this device. I'll be interested to hear the results.

I'm actually building stuff at the moment (not just faffing around on breadboards as usual), so I should have something to show for it (eventually). I'm working on a proper (but miniature) lunetta at the moment. I might have a look back at some of your circuits for the Modular Lunetta and Bandersnatch for inspiration (don't worry, you'll get credited for anything that inspires me). I also want to start doing some proper recordings soon, rather than my usual random noise recordings.

I shall look out for further installments...

Gary

PHOBoS · Last edited by PHOBoS on Thu Feb 28, 2013 9:15 am; edited 1 time in total

The cat's not dead yet Laughing

(I'm thinking of making a full schrödinger synth out of it Shocked

).
I look forward to see what you're working on and it would be great if you could make use of some of the things I've posted Very Happy

--------------------------------------------------------------

ok here's the first schematic (I'll post it in bits, since it's quite large and easier to understand in parts) . The Gate and Trigger circuits aswell
as the external control inputs for the keyboard. I've only drawn it for 2 keys, but in reality there are 10.

starting of with those, the keys of the keyboard are just switches that connect a 'KEY' point to the positive supply of the keyboard (3V),
so it's pretty easy to control these with an external signal. I want to use an input voltage in the range of 5-12V which would probably fry
the circuit in an instant. So I added a voltage divider (33K + 68K resistors) which has an output voltage of 3.3V with an input of 5V.
With the voltagedrop over the diode that's in series, there will be ±2.7V left, which is a safe value and enough to trigger the keyboard.
And if the input voltage is higher then 5V, the zenerdiode will still keep it at that.

next the Gate circuit which is very simple. An OR-gate made with diodes and a resistor, followed by a transistor, because the voltage is too
low to trigger a CMOS gate directly, which is in turn buffered by a schmitt trigger inverter (40106). Because the transistor allsoy inverts,
there is no need to add an extra inverter.

The trigger circuit also includes the LED indicators. The transistor, in combination with the 1nF capacitor and pull up resistors (one in series
with the LED), creates a very short high to low pulse.The pulses of all the keys are then combined, again using the same diode resistor configuration
of the OR gate but inverted, so with a pullup resistor and the diodes reversed (it's an AND Wink

). If you're looking for the pull-up resistor it's the
1M attached to pin 5 of the 555 timer. The 555 is used in monostable mode and turns it a into a neat trigger signal. The 10nF caps attached to
the base of the transistors are to debounce the keys of the keyboard.

more next time sleeping

NOTE: the current through the zenerdiodes is too small for them to work, so in the final design I placed 4K7 resistors in parallel
with the 33K resistors.

Lun-A-Key - Gate and Trigger.gif

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PHOBoS · Posted: Mon Feb 25, 2013 10:03 am Post subject:

it's starting to take shape Very Happy

lunkeyboard11.jpg

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Lun-A-Key case, not completely glued together yet.

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PHOBoS · Posted: Mon Feb 25, 2013 3:18 pm Post subject:

lunkeyboard12.jpg

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a bit of color added

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PHOBoS · Posted: Mon Feb 25, 2013 5:29 pm Post subject:

lunkeyboard13.jpg

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first parts added to frontpanel

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wmonk · Posted: Mon Feb 25, 2013 5:55 pm Post subject:

PHOBoS · Posted: Mon Feb 25, 2013 6:45 pm Post subject:

Thanks

I got that keyboard (incl. keys) at one of those €1,- shops a couple years ago. I have some slightly different, animal shaped ones too Laughing

.
If you need small keys visit a toystore, they usually have some small cheap keyboards or if you're lucky you'll find something at a
'kringloopwinkel' (no need to translate that for you Wink

)

kkissinger · Posted: Mon Feb 25, 2013 6:52 pm Post subject:

Very nice project, Phobos. Look forward to hearing it!

PHOBoS · Posted: Mon Feb 25, 2013 7:43 pm Post subject:

Thanks kevin Very Happy

I hope to finish it in the next couple days, maybe even wednesday if everything goes as planned Laughing

And then I'll play around with it and record some sounds.

Draal · Posted: Tue Feb 26, 2013 5:31 am Post subject:

Things are really shaping up! Been busy working on my tube guitar amp and a mini synth to follow this until recently.

I wish I had these wood skills myself. Very Happy

PHOBoS · Posted: Tue Feb 26, 2013 7:51 am Post subject:

oh, but your woodworking skills are amazing Draal Laughing

just different.

It's all done with a (electric) jigsaw, a file, some sanding paper, sweat and a bit of patience. And I don't use real wood, which makes it a lot easier
to work with. Everything is just glued together by the way, no screws or nails.

----------------

Switches, pots and knob did arrive today as planned so I can continue with that. I did have another idea yesterday which is using the inputs
that control the keyboard also as outputs to control something else, so you can use the keyboard as a row of 10 pushbuttons. I allready have
toggle switches to turn the inputs off so I could do it,. but it would need some extra buffers though.

PHOBoS · Posted: Tue Feb 26, 2013 7:55 pm Post subject:

frontpanel and keyboard wired up. I'm almost done with painting the case, but you'll get to see that when it's completely finished. (maaaaybe tomorrow) Cool

lunkeyboard14.jpg

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frontpanel and keyboard wired up

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Draal · Posted: Wed Feb 27, 2013 8:16 am Post subject:

The progress on this has been fun to watch. I know I have a kiddie keyboard somewhere in this house of toys Rolling Eyes

.

analog_backlash · Posted: Wed Feb 27, 2013 1:08 pm Post subject:

Really boring question PHOBoS. It looks like you're using MDF for your housing(s). How thick is the piece that you're mounting the controls on? I only say this as I tend to use a lot of 3.5mm jack sockets and I usually have to mount them on aluminium, steel or plastic sheeting, as the thread lengths are so short. I think that MDF will be too thick (or so thin that you could put your finger through it Crying or Very sad

).

It looks like it's coming along nicely, by the way.

Gary

PHOBoS · Posted: Wed Feb 27, 2013 1:39 pm Post subject:

Yes it's MDF, the front is 4mm which is indeed too thick for sockets, but I've still managed to use them by using a chisel and carving some
layers away, If you have a completely round 3.5mm jack socket it's easier because you can use a large drillbit, I've done this for those
DC input jacks. But be careful if you do it this way,. don't put it in a drill just turn it carefully by hand. You might be able to use a drillpress
but you would have to be VERY careful, else you just end up with a large hole.

here's an example from my PWM lunetta,.. look at the sockets at the top:
Posted Image, might have been reduced in size. Click Image to view fullscreen.

Posted Image, might have been reduced in size. Click Image to view fullscreen.

the sides and top are 8mm btw and I used a heavier 12mm piece for the bottom to add some more stability. (I used 18mm for the Bandersnatch).
-------------

I now have everything wired up,. so next is going to be the hold-your-breath-and-turn-it-on-and-hope-there-isn't-any-smoke part. Shocked

The painting set me back a bit timewise, I'm doing a duotone but one color kept messing up the other. I think it's ok now just needs some
clear coating. If I can resist I'll let it harden further until tomorrow before I put it together, allthough it will be dry enough to handle.

PHOBoS · Posted: Wed Feb 27, 2013 2:24 pm Post subject:

I wired the LED's the wrong way around doh

(I usually have them connected to GND). But no smoke, I've got power on all the IC sockets
and I get 2.7 V when I press a keyboard key. So that's right sofar. Laughing

so a little bit of rewiring and then I'll try again,..

analog_backlash · Posted: Wed Feb 27, 2013 6:10 pm Post subject:

Thanks for the MDF advice. I've looked at the Wickes website and they do 3mm board, but that's probably still too thick and a bit flimsy. I think that your solution is the best compromise. MDF is cheaper than metal/plastic sheet and easier to cut, so I'll give it a go...

PHOBoS · Posted: Thu Feb 28, 2013 8:55 am Post subject: