increase the range of a variable resistor?

Whuffle · #1 Jul 21, 2005, 12:53 PM

Hi people!

I need to replace a 200k potentiometer with a touch-sensitive strip, itself being a type of variable resistor.

Unfortunately I have no choice in the matter: the strip has a resistance between 3k and 20k. Is there some way I can ensure that 200k is the highest resistance available, while leaving 3k as the lowest?

I had wondered if there is such a thing as a voltage-controlled resistor, a sort of inverse-transistor? That way, i could use the touch-strip to control a stronger resistor, perhaps.

Any thoughts?

labman · Jul 22, 2005, 07:55 AM

This question goes beyond my limited knowledge. I may have helped on the last one, but not this one. Sorry.

Whuffle · Jul 22, 2005, 09:56 AM

lol, my neighbours hate you enough already, labman!

Ok, i think i have cracked it anyway.. i can use my touch-strip resistor to control an LED, which in turn will affect a Light Dependent Resistor of much greater ohmage.

fizixx · Jul 29, 2005, 04:30 PM

Ok....what do you mean by a touch-sensative strip? Go into a little detail so folks here know what you're asking.

Whuffle · Aug 5, 2005, 09:44 AM

Touch sensitive strip:

available from http://infusionsystems.com, or can be made yourself

It is basically a conductive wire over which is placed (but not quite touching) a stip of resistant material: a semiconductor. the wire constitutes one polarity in the circuit, and the strip is the other.

Hence, when touched together, electricity is caused to flow. The device will have a resistance that varies dependent upon WHERE the strip is touched.

I am purchasing one rather than making it, since they are more durable, less than 3 mm thick, etc etc..

I intend to use this form of variable resistor, rather than the "pot" form of variable resistor that is in my Wah-wah pedal (guitarist's effects pedal for those that don't know)

However, the resistance of the strip is between 3k and 20k, depending where it is touched, whereas the Pot it will be replacing is 100k (i have aquired a different circuit, so it isnt 200k as i originally stated) and I need to ensure that everything matches-up.

fizixx · Aug 5, 2005, 10:15 AM

Ok, now it makes a little more sense. Thank you.

fizixx · Aug 5, 2005, 10:43 AM

How about you try using op-amps? Like a comparator; one for the low end and one for the high end.

??



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