Resistor Detection Circuit

Thread Starter

ConnaTC

Joined Jun 20, 2020
18
Hi Guys I’m looking to build a circuit which will light an led when it detects an 420k resistor will i require a transistor circuit for this to work?

If this post is in the wrong section I apologise i am a new user?
 

ericgibbs

Joined Jan 29, 2010
10,463
hi C,
So a Bridge, made up of say one 420K and the other half of the bridge say 10k's, a AD623 INA [ OPA] driving a transistor LED or Buzzer, powered from say a 9V battery could work.
Make the circuit detect a Zero balance .
E

Update:
Is it always going to be 420K, also what resistance tolerance is acceptable.?
 
Last edited:

Thread Starter

ConnaTC

Joined Jun 20, 2020
18
That could work il have to look into AD623 to make something up


hi C,
So a Bridge, made up of say one 420K and the other half of the bridge say 10k's, a AD623 INA [ OPA] driving a transistor LED or Buzzer, powered from say a 9V battery could work.
Make the circuit detect a Zero balance .
E

Update:
Is it always going to be 420K, also what resistance tolerance is acceptable.?
 

Thread Starter

ConnaTC

Joined Jun 20, 2020
18
Many apologies i got the resistor value wrong its 470k not 420k in regards to your question it should always be 470K so the tolerance can fluctuate quite a bit if needed
hi C,
Check out my update , post #8, there maybe a cheaper , simpler way.
E
 

KMoffett

Joined Dec 19, 2007
2,899
For a Go/NoGo circuit a 470k half bridge and a window comparator with adjustable upper and lower trim pots. No need to read and think. ;)
 

ericgibbs

Joined Jan 29, 2010
10,463
hi C,
As the 'Accept on Test' resistor value is always 470k , I would go with post #12.
A DMM test meter is a useful piece of kit to have in your toolbox for other tests you may have to do.

E
 

Dodgydave

Joined Jun 22, 2012
9,307
BT phone sockets have a 1.8uF cap between pins 2,3 and a 470K resistor between pins 3, 5. .

..best solution is a DVM as posted earlier...
 
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