Scale resistance range?

[iam229]

Friend and I are trying to build a ribbon controller, like this one:

http://www.youtube.com/watch?v=rexNt0Tau_o

Our problem is this: Our ribbon runs a resistance of 50kOhm to 500kOhm from lowest end to highest end, and the Timer circuit will give an output time proportional to the RC value. With a gigantic R value, the output sound becomes very low frequency(3hz) and cannot be heard.
I cannot change the capacitor value, it is already the lowest we can find...

So we need a way to reduce resistance on the ribbon. We cannot simply put the ribbon in parallel with a small resistor, because then the ribbon becomes useless as all the current goes through the small resistance, and the effective range of resistance becomes 1k-1.1k, making the instrument a near monotone.

SO, question is this:
Is there a way we can SCALE the resistance on the ribbon, 500k-50k near linearly to a smaller value, say 10k-1k? Such method would help us tremendously.

THanks so much!
-Evan

 

[ScottyUK]

What is the smallest capacitance you can find?


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If we learn from our mistakes I'm getting a great education!

 

[waross]

Use a wider ribbon.
Buy a foot of two conductor cable and use that for a capacitor. If the capacitance is now too low, use a longer cable.
It is difficult to determine exact circuit details from the video. Perhaps look for a different video.

Bill
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"Why not the best?"
Jimmy Carter

 

[iam229]

Hey, the smallest capacitance I can find is about 10nF. Is there no way to scale resistance though? Some kind of intermediate steps with amplifyers perhaps?

 

[ScottyUK]

I can readily lay hands on caps down into the pF range, although you start to worry about parasitic capacitances between circuit board traces when you are in the pF range. 10nF is still pretty big - 1nF would move all your frequencies into the audio range.

Easy!


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If we learn from our mistakes I'm getting a great education!