Critical resistance situation

I'm in a situation where my resistance changes between two states (infinity and 500 Mega ohm ).I want to be able to notice a change when it switches from one state to the other state.

Unfortunately I can't change the value of both states.

My question is , Is there a bridge or a certain circuit whose total resistance depends on the existence of a specific resistance.

In other words, I want the bridge or circuit to give a normal total resistance (10k or 100k or whatever) when my resistance is injected into the circuit and open circuit when my resistance is removed.

Can I do that ? Can I do with passive elements ?

If this is not possible with passive elements , what circuit should I use ?

by ahmadsayed
October 14, 2018

Yes, that is possible, but very challenging.

First you must realise a very high standard of cleanliness and keep everything very dry.

Then I need to know more about your sensor, the 500M/infinity resistor.

  1. Is one end grounded?

  2. What is the highest voltage that can be applied across your resistor without causing sparking or inaccuracy?

Thanks. mike

by mikerogerswsm
October 15, 2018

The sensor is a MEMS sensor which has two terminals .. one for actuation from a dc supply and one connected to the ground of the supply..

highest applied voltage is 8 volts

by ahmadsayed
October 15, 2018

I would suggest detaching the MEMS from ground and putting in a 1M resistor. Make this one side of a bridge, and add resistors to make up the other side of the bridge. Then use a comparator to compare the bridge voltages. Will post circuit anon.

by mikerogerswsm
October 15, 2018

https://www.circuitlab.com/editor/#?id=vqq6ywz6tn3v

by mikerogerswsm
October 15, 2018

The LF111 is obsolete, use LF356 instead.

http://www.ti.com/lit/ds/symlink/lf356.pdf

by mikerogerswsm
October 16, 2018

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