Trimmer Pot advice please...

[jamiewoody]

i want to make a keyboard! (the angels sing "AAAHHHH!"). i've finally figured out how to do this! i have some more prototyping on the breadboard to do, but it will happen,

but, my main point of this thread is on trimmers. i want to use NO push button switches wired to a trimmer for the keys. the trimmer will TUNE the "key".

a two-fold question. first, would 500k make for wider pitch range? second, are 500k trimmers available? i realize trimmers are for "fine" tuning resistances normally.

also, on push buttons, what kind do i need to buy? i mean, i want one which will not "click" physically or in the circuit. do i need to look for the word "momentary?

[Gordonjcp]

It's really hard to get buttons that don't "click".  Maybe a good bet would be to cannibalise a cheap crappy keyboard that uses metal springs as contacts.  The downside there is that any variation in resistance as the contacts get oxidised will make your pitch vary - not too badly, with a bit of luck.

You could use 470k trimmers, which will be easier to find than 500k.

[jamiewoody]

yeah, on buttons, if worse comes to worse, i can make something. i hate to do that, really. perhaps a key, a piece of something conductive under it, a spring or a rubber grommit under the key to build it up, then when pressed the key makes contact.

the more i think about it, the more i''d like to actually use a real keyset for this. of course, in order to do one octave, i need at least 12 buttons. but, i would do 14 buttons, so i can have one inversion and one 9th note. i only want to use it as a lead instrument...

i have not seen a lot of people making keyboards from scratch. circuit ben made one which turned out great! tomommi has a 4 note keyboard in one of his boxes, that is about all i can recall.

of course, i want to circuit bend bass pedals from an old organ too! ;-) i started a thread for that one if you have advice for it...

[jamiewoody]

thanks for the advice on the trimmer...there is little difference, in this application, between a 500k and a 470k i think...

[Ciderfeks]

Wouldn't regular NO, push-to-make (non latching or momentary) buttons do the job? If you don't want the "click" and resulting latched "on"status, then the non-latching bit is important. Here's some at Rapid Online in the UK

http://www.rapidonline.com/Electronic-Components/Switches/Push-Button-Switches/Miniature-push-switches/64324/kw/push+to+make

http://www.rapidonline.com/Electronic-Components/Switches/Push-Button-Switches/SPST-Push-switches/71430/kw/push+to+make

And Mouser in the States have loads too, they have some really nice multi-coloured illuminating ones which would work great as a keyboard, with a different colour for each note...

http://gb.mouser.com/Electromechanical/Switches/Pushbutton-Switches/_/N-5g30?P=1z0x3scZ1z0z2vt

Or how about using computer keyboard keys? You could use the appropriate letter for each note.

Casper has a schematic of a keyboard system he built into a Speak & Spell using push buttons with trimmers to alter the pitch that you might find useful, although he used momentary buttons underneath regular keys. Anyway, if you haven't seen it the schematic is here:

http://www.casperelectronics.com/images/finishedpieces/speak-n-spell/Speak-n-Xbending/SpeakAndSpell2.jpg

[jamiewoody]

i think they would need to be momentary switches. to make a musical keyboard, the buttons need to trigger a sound, i have a feeling if i do not use these, i will have to press the "key" twice.

so, is momentary the same as one way switch? i only want to trigger a tone, not switch a circuit off to have to switch it on again.

[Gordonjcp]

Momentary is what you want, but most buttons will click.  Think about the clicky switches on the front panels of equipment.  You can actually buy those on eBay.  Search for "tactile push switch" or "momentary push switch".

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=220398445490

Those look like they have rubbery buttons that won't click, but the thing to watch with conductive rubber is that the resistance changes when you push it harder!  So you might end up with some unintended aftertouch...

[jamiewoody]

thanks for all the advice. i will read it all again...slowly...before i buy a slew of them.

the keyboard thing is different for me, since it is also very mechanical. but, the wheels are turning and i have some ideas. the more i think about it, the more i think i could make a switch. maybe an actual keyset (or partial KS) with a conductive mechanism under it. aluminum or copper...some sort of metal reed type thing which will bend to the other contact point. the problem with that is, it has to "bounce back to shape".

as much of a pain as it might be to set up, the spring loaded under the key sounds like a good idea. i think i may have a cheap keyboard, that was unbendable, which has med size keys, that actually has springs under the keys.

[Ciderfeks]

If you check that Casper schematic, he uses this type of push-to-make button under his keyboard:

http://www.rapidonline.com/Electronic-Components/Switches/Push-Button-Switches/Miniature-push-switches/64324/kw/push+to+make

These are standard "non-latching" momentary buttons often used in the loop advance bend on Speak & Spells etc. They have a spring inside them and make no clicking sound when you press them and the connection only stays "on" for as long as you press em. The latching type do "click" and stay on when you press them and only turn off after a second press, like in a stomp-box. You don't want those. As Gordon says most of the tactile switches, like you get under the buttons on synths etc do make a clicking sound, even if they don't actually latch on.

[jamiewoody]

"non-latching" momentary buttons...thanks! they look pretty standard. should be able to find them easily.

i am not familiar with a casper keyboard,,,link please? i have seen most of his site.

[Ciderfeks]

Hi Jamie, I guess you missed the link in my previous post above 

Anyway here's the link again: http://www.casperelectronics.com/images/finishedpieces/speak-n-spell/Speak-n-Xbending/SpeakAndSpell2.jpg

It looks like something similar to what you're talking about and although it's triggering tones from a S&S, it's still a keyboard built around momentary switches and trim pots. Hope it helps.

[jamiewoody]

thanks...letting this huge drawing load right now! lol