has anyone ever made a keyboard...

[jamiewoody]

from scratch?!

here is an idea i have...please dialogue with me, as i haven't tried it yet.

harvest some plastic mini-keys from a dead casio...

i could plant some normally closed switches under the keys, you get the picture, press the key, and  the switch is activated.

i could experiment with different caps, since they seem to produce lower tones in the higher values, and wire each cap to a resistor and a trimmer.

the series of cap-resistor-trimmer on all of the keys would be wired in parallel to the synth circuit. i could do a circuit with different synth types i have been learning to build, cmoss, 555, 556...

my theory (or lack of! lol!) is that i could perhaps "tune" each key with the trimmer pots, so there will be a set pitch for each key. i would prolly only do a two octave keyboard.

of course, the box would be very "moog" looking, with wood on the sides, etc!

so, what do you think? any problems with this idea?

[Gordonjcp]

It wouldn't really stay in tune.  Analogue synths used to use very high-precision resistors in series, with the pressed key shorting a proportion of them.  The resistor ladder formed part of a potential divider that went into a very carefully-adjusted amplifier and gave a linear output voltage proportional to the note pressed.  This then got fed into a logarithmic amplifier (fiddly as hell) and then into a voltage-controlled oscillator (actually, current-controlled but we can gloss over that - also fiddly as hell).

Dig out the circuit diagram for an analogue monosynth for an example.  The Powertran Transcendent 2000 had a circuit like that for the keyboard.

[jamiewoody]

thanks. may go out of tune huh?

all i can do is try things and see if they work.  the more i experiment, the more intuitive i become!

[crossedout]

look for the "toy organ" schematic here:

Engineer's Mini-Notebook - 555 Timer IC Circuits

[phantompowers]

Nice one for posting that notebook. I've been after that for a while.

[jamiewoody]

no doubt! forrest mims is a futuristic folk artist! ;-)

[jamiewoody]

this WILL be my next book purchase!!!

[jamiewoody]

i saw a youtube vid of a homemade electronic keyboard, and  i exchanged some email with the one who made it. he made a basic VCO, and came out with a capacitor, then from the capacitor, did a parallel circuit of trimmers andN/O switches. of course the push button switches were the keys, and the trimmers tuned the keys.

it seems the MIMS model is a little different, there are different values of capacitors for the keys.

which seems better?

[zoomtheline]

Thought about it then thought it would be shit if I did it.

(Apologies for pointless rubbish post but needed to post something so Admin didn't delete my dusty account)

[Timodon]

Good idea!

I made a very rudimentary 3 tuneable key (or 3 button) version of a keyboard on my Betasynth. The pots were all in parallel on the same oscillator of a hex schmitt trigger. As well as tuning eacfh key for a simple three note melody or bassline the fun thing about that was that the pots have a weird relationship with each other when pressed at the same time. Different notes are produced by pressing different combinations of keys - not great if you wanted a precision instrument but good for the kind of music I wanted to make with it!

[jamiewoody]

using a schmitt trigger seems like a good idea, since there are a quadzillion different sounds that can come from one!

i threw together a stepped tone generator with a 556 on the breadboard. i hooked up a switch (normally closed, i need normally open instead), and i learned i was able to trigger a tone using the button. but, when i would twist a potentiometer, the pitch would change.

i would love to make a "mini-keyboard" and make an oscillator for it, which would effect the waveform yet not change the tuning...