New bender - another Chad Valley Keyboard

[samspike]

I found this forum thru Google.  New poster here. New to circuit bending.

First project: a Chad Valley keyboard.  It's similar to the one in the 555 timer/chad valley thread, and the Argos thread (which I've lost and can't seem to find again).

Compared to the 555 thread:
- Mine has 15 demo tunes, buttons in straight line
- No red star buttons, or buttons in that area
- Circuit board is different
- Blue case

Compared to the Argos thread:
- Mine is mono, and no record function as far as I can tell (I think Argos thread mention bi-note poly)

I also have 3 keys on piano keyboard that don't work (any hints how fix?)

I've add a jack output although not wired it in yet, as I can't decide whether to remove the speaker, make it switchable, or just it in.

One other thing: I was looking at the 555 timer thread, I saw a 100K pot in there.

I tried various pots in mine between battery and main board (for both red and black).  Most seem WAY of range.  A 75 ohm, seems closest, but push it too far and the keyboard cuts out coimpletely.  I put a 100 ohm resistor in parallel with the 75 ohm pot to cut its range, this helped a bit, but didn't solve the problem.  Hints anybody?    Why I my values so incredibly different from those in the 555 thread?

In range the 75 ohm produces some bizarre effects, pitch bending, and there is this 2 note start-up tone when you turn on the keyboard.  It kind of goes into an endless bleepy loop if you get the setting just right?

[samspike]

I managed to fix the missing keys - there were two pins on the ribbon connecting keys to PCB that were dodgy connections.

[Circuitbenders]

can you post a link or two to the threads you are referring to?

I assume you are trying a voltage drop crash control with a pot between the power and the circuitboard. I'd go for the red wire and make yourself an A-B pot with some resistors. Theres some details in the huge Casio SA1 thread http://www.circuitbenders.co.uk/forum/index.php/topic,29.60.html .Find a point just before it crashes completely, measure the restance of your pot and use that as the maximum resistance, but bear in mind that the values will probably change as your batteries run down.

Where on earth did you find a 75 ohm pot?

[samspike]

Thanks.

Yes the voltage crash sort of works, you have to position it exactly right to make it work.

I'm using a 1K pot, with a 1K resistor in parallel.  That works, although the usable range is narrow.

I've also installed a switch to activate the crash, and a jack out.

The keys work, but the demo buttons are a bit flakey. The reason is there are two internal ribbon cables, and they are very badly soldered/glued on (my roughness didn't help) - as soon as I opened the keyboard I was in trouble on that.

BTW: The 75 ohm pot, came from Maplin.  I bought a bag of assorted pots, and there it was.  Blue in colour.  It's got 75 ohm printed on it.  I measured it with multimeter, and that says full on it's about 100, and half way about 50.


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I've got a Casio SA-8 to play with now, so having done my practise project, and not messed it up too badly, I'm moving on to that.  I'll do it right this time - I hope.

I really like the SA-8 so I don't want to mess up this time.  I'll read the SA discussion carefully, and take a lot more care building.  I'm pretty confident I can do it right (though nervous about soldering to ICs)

I don't really want to remove the speaker from the SA-8, so I'm thinking about alternatives.

Options:

1. to put the pots/switches on the overhanging bit of black plastic above the row of buttons.  The problem: Wires hanging out.

2. Build a 70s-style wooden case, and mount the keyboard in that.  Problem: Keyboard is light and portable now - don't want to loose that (that's one of the reasons I don't want to lose the speaker).  Also I need to put a new battery compartment as it will be inaccessible (or connect a DC adaptor to mains, which I'm nervous about doing for circuit bent instrument).

[Circuitbenders]

I'd go with the wires hanging out on the SA. If you do it neatly and use cable ties to keep everything together you shouldn't have any issues.

[Bogus Noise]

I recently found a bunch of lower value pots in 20ohm, 50ohm, 100ohm, and 200ohm.
Didn't know of a source for anything below 470ohm before. 75ohm is a bizarre one though!

http://www.jprelec.co.uk/store.asp/c=260/Wirewound-Potentiometers