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Subject: how does an op amp work?

Date: 11/16/02 at 3:57 PM
Posted by: Jason Warnett
E-mail: big_bird_takes_drugs@hotmail.com
Message Posted:

how exactly does an op amp work? ive been given a circuit to detect moisture, but i only understand it to a certain extent. From what i understand leg 2 is the 'reference voltage' and whe input to leg 3 decides wheather it is inverted or not. electricity always tries to take the easiest route round and as water conducts electricity i assume this decides what is going into leg 3.
----------------o-------------o----------------------- +9v
| | |
| 100k variable |
100k resis | |
| o-----------|\| |--|>| LED-|
| | | >---680R--o o-- 0V
o--------------/\----------|/| |--|<| LED-|
| | |
=(moisture 1M ohm resis |
| sensor) | |
| | |
| | |
| | |
----------------o-------------o---------------------- -9V

This is the circuit. the circles symbolise the joins. /\ means the wires do not connect where 2 of them cross. one LED turns on when there is moisture, the other one when there is not. I dont quite understand why this happens and also which LED goes on when. Please explain it to me since i am very confuzed and this is used as one of the basic building blocks of electronics.

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