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### Topic: Memory Opamp (Read 1 time)previous topic - next topic

#### -SaRaH-

##### Aug 11, 2012, 08:25 pm
Hey.. Can someone let me know how this circuit works?

http://www.freeimagehosting.net/4iynj

#### Krodal

#1
##### Aug 11, 2012, 09:08 pm
I can see how it works, but I can't explain it.

The (-) input is kept at a voltage above the middle with the 3k3 and 10k.
The (+) input is the middle between the output and the power (perhaps 5V or 12V).

The 'set' pulls the (+) input to ground, so the (-) input is higher, resulting in a low output and the led turns on. The low output keeps the (+) input in the middle, so that is still lower than the (-) input. The output stays low.

The 'reset' make the (-) input always lower than the (+) input, so the output goes high. If the output is high, the (+) input is always higher, so the output stays high.

Does this explanation make any sense ?

#### James C4S

#2
##### Aug 12, 2012, 02:18 am
Throw it in to:
Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com

#### -SaRaH-

#3
##### Aug 12, 2012, 06:19 am
I really dont understand what you said. I can understand how, but I need to know why this is used.

Should I download something from here.. I dont know where to input my ckt.

{{{{{{{{{
Circuit:
http://www.freeimagehosting.net/4iynj
}}}}}}}}}}

#### justjed

#4
##### Aug 12, 2012, 04:06 pm

I really dont understand what you said. I can understand how, but I need to know why this is used.

The "why" can be due to many factors. The person deciding how to build the circuit would evaluate all those and build the circuit a particular way. One of those factors might be, "that's the parts I have on hand". Or maybe it's a circuit to demonstrate the use of a particular component. We could speculate endlessly on this. Perhaps you could supply some context?
... it is poor civic hygiene to install technologies that could someday
facilitate a police state. -- Bruce Schneier

#### Runaway Pancake

#5
##### Aug 12, 2012, 04:17 pm
Quote
Can someone let me know how this circuit works?

Clue:  hysteresis
"Who is like unto the beast? who is able to make war with him?"
When all else fails, check your wiring!

#### -SaRaH-

#6
##### Aug 12, 2012, 05:04 pm
Context..errmm.. This was designed by Alan Tyger. and its called Flip-Flop Memory Op-amp.

The op-amp has a positive feed back and I know that it has something to do with hysteresis..I tried to understand, but just cant figure out how this works..

#### Runaway Pancake

#7
##### Aug 12, 2012, 05:44 pm
It's an RS latch (without a complementary output.)  http://cs.fit.edu/~wds/classes/comp-org/Logic/sequential.pdf
I don't know who Alan Tyger is, but that circuit is as old as the hills.
It'd be better to use a dedicated comparator.  A comparator can be made from an opamp, but a comparator (LM339) is better suited to the task.
"Who is like unto the beast? who is able to make war with him?"
When all else fails, check your wiring!

#### -SaRaH-

#8
##### Aug 12, 2012, 05:49 pm
oh.. Ok.. so the link which you gave me is similar to the circuit which i posted?

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