Circuit that senses if resitance is going up or down

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jrstech

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Im looking to make a circuit that can close a switch when the resistance is rising or the other way around ( switch would be closed when resistance is dropping). Any ideas?

thanks
 

use the resistor in a voltage divider in which the varying resistor is in the upper arm and detect the voltage if you want to detect falling of resistance and in the lower arm to detect rise in resistance....
 

jrstech said:
Im looking to make a circuit that can close a switch when the resistance is rising or the other way around ( switch would be closed when resistance is dropping). Any ideas?

thanks
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A very simple way is to force a constant current through the resistance. Use the voltage as one input of a comparator and compare it with a reference voltage. If the resistance increases, then voltage (I*R) across it increases and causes the comparator to trip. Use the comparator's output voltage to control the switch (a simple CMOS switch).
 

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