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Instrumentation Op-Amp with Variable gain

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nealkb

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I am trying to build an instrumentation op-amp for sensing microvolts. The problem is I don't know how small the signal is, and therefor how much amplification is needed.
I am planning to use a cd4066 quad bilateral switch controlled by a CD4106 hex scmitt trigger to switch to different gain resistors.
In order to know which resistor it is going through, I am hoping to use a led. This brings up burnout, and to combat this I have been advised to use a transistor.
I need help figuring out how to get protect the LED without using the resistors that are essential to my measurement.
Thanks for the help!
Neal
 

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