[sdiy] Log Amp revisted

[Tom Arnold]

Just again to pass on something I learned the hard way.

While making this pot -> voltage converter I found my linearity problem.
I'm doing a current to voltage circuit, pot is connected from +V to ground
through a fixed resistor and I measure the voltage drop.  Well, if that
resistor is much smaller then the max resistence of the pot, things got
non-linear real quick ( 120k pot with 10k resistor ). I did this to stay
away from the supply rails...  so I bump this fixed resistor up to roughkly
equal the pot and now things are much more linear, and I use a diode to keep
me off the supply rail so the TL0xx stays happy.

Gonna move it off protodeathboard to perfboard tonight and if it works as
well in practice as on the bench I'll post the simple schematics for y'all
to poke holes in. ( IBM joystick -> X/Y CV and two triggers ).  You can
build one of these for about $10 including the cost of the joystick, in fact
I bought 4 kraft joysticks off ebay for $10 including shipping so I think
its a definate neat toy to play with...

-- 
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 - Tom Arnold       -  Free Synth DIY webspace http://www.sdiy.org 
 - SynthGeek        -
 - BBD Fanatic      -  "...is it a virus, a drug, or a religion?" 
 - echo evho wjxo   -    Juanita Shrugs. "What's the difference?" 
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