Convert resistance to a open closed contact

[drkmaguire]

I am trying to find a device that will convert resistance to an open/closed contact.

Basically I have a security device that works on open closed conditions, I now need to be able to protect the cable from tamper and the only way i can see doing this is to use resistors at the end of the cable.

The problem is my security device does not recognize resistance, so i need to convert the resistance to either open/closed state plus a third state for a tamper, for example if i use a 4k7 resistor

4k7 will equal closed
9k4 will equal open
0k/ infinitive will equal tamper

I have tried seach for a device that can do this but have had no luck, could you please let me know if such device exists or weather it would be possible to make this device

thank you

 

[A.Anand Srinivasan]

please post your schematics... your description on where the resistor is placed and when it is opened and closed isn't clear....

 

[turbina]

if you use konstant current generator you can read voltage on you resistor and make decisions on voltage variations.

 

[elektronic]

a simple solution is to use a Wheat·stone bridge and a comparator

 

[jrstech]

Im looking to do to something similar but I need my switch to close at specified resistances that are coming of of a potentiometer. Let me know if you come up with a solution.

 

[A.Anand Srinivasan]

make the potentiometer as one arm of a voltage divider and use comparator to switch an MOSFET by the way of voltage level detection....