Re: Analog Senors to Midi

Mark Coniglio (
Mon, 15 Mar 1999 16:57:35 -0500

Well, this may be boring technical details to some, but here goes:

The flex sensors can provide an input to simple op amp circuit, where the
changing resistance changes the output of the op amp; (you'll need to view
the diagram below with a monospaced font in order to see it correctly.)


R1 | |
/ | |- |
+V <-\/\/\/\-+----| -- |
/ * | -- |
I in | -- ----+------- V Out
GND --------------| --
| --

R1 is the flex sensor, R2 is the feedback for the op amp. (R1 could be any
variable resistor, BTW.) This is a classic example of a trasimpedance
amplifier where an changing input current (provided through R1) is
amplified and output by the op amp.

The gain of the circuit is -R2, so if R2 is 1000 Ohms, the gain is -1000.

The current at the point marked "*I in" is what is being amplified.

Remember that the output is not linear, but exponential because of Ohm's
Law: I = V/R, i.e., I (current) will grow exponentially as R (resistance)
gets lower.

For more help with this stuff, try the Radio Shack "Engineer's
Mini-Notebook - Op Amp IC Circuits" for examples and diagrams. Catalog #
276-5011. Please note that all scientific discoveries up to and including
quantum physics are covered by these little books you can purcahse at Radio
Shack. ;-)

And now, we return to our regular program...


Mark Coniglio, Artistic Co-Director |
Troika Ranch Dance Theater |