Please help can't figure this out, been trying for ages

That is called a window comparator:

Best to use comparators, not opamps. You need devices with very low offset voltage, plus a precision reference, plus very narrow tolerance resistors.

--
Regards, Joerg 

http://www.analogconsultants.com/

omfg this looks like it will do exactly what i need when reading about them on wikipedia!!!. thank you so much i was trying so long to make something with mosfets, resistors and different branches and i was getting nowhere. i love you forever!!

This is a toothbrush, this is a comb, this is a resistor, this is a voltage.... Sheeeeeesh >:-} ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| STV, Queen Creek, AZ 85142    Skype: skypeanalog |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
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     Thinking outside the box... producing elegant solutions, 
              by understanding what nature is hiding. 

"It is not in doing what you like, but in liking what you do that 
is the secret of happiness."  -James Barrie

Note that those are open-collector (drain) comparators.

You could also use two active-output comparators and a logic gate to combine them.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

So we all have to start somewhere, of course with the exception of the mighty JIM born with a scientific calculator and a Rigol portable.

the "right answer" isn't to go hunting for unicorn-components to build such a circuit it's to come up with some other way to do what you need to do that doesn't involve such a yucky requirement.

Certain types of circuits you don't see very often probably not because engineers don't like a challenge but certain things just nobody knows how to do for a cost/time investment that makes it worth the trouble. I'd say a window comparator that distinguishes between the arbitrary/bizarre voltage levels of 1.5959 and 1.62035 volts would fall in that category. what process in nature requires those two voltages exactly as reference points and not some other representation? Maybe use a precision amplifier to amplify the signal first and relax the constraints on the comparator? That's what they invented DC amplifiers for, after all.

IMO the "right answer" when you've been trying to do something "for ages" and it's not working out is to stop trying and come at the problem from another angle. Not keep smashing your head against the wall.

Avoid the "sunk cost" fallacy and don't be afraid to scrap and clean-sheet designs that start frustrating you every minute you spend thinking about them, even if you've already invested time in them/it seemed like a a good idea at the time. You'll be glad you did

voltage is between 1.5959 and 1.62035 volts. The output voltage should be zero when the voltage is higher than 1.62035 or lower than 1.5959. How do I implement this using OP-AMPS, transistors and passive devices? Is this eve n possible? Thanks for any help! No digital solutions please.

That's certainly been my experience, and reflects my normal practice.

Looking at the results of a couple of hours work and deciding that that app roach isn't going to work well enough is definitely part of my design proce ss.

There's an Irish joke about somebody being asked for directions, and giving the reply that if he'd want to get there, he wouldn't have started off fro m here.

--
Bill Sloman, Sydney

I guess a bit of compassion is a far ideal for engineers.

In other words he already learned something but doesn't realize it. Whatever he's doing shouldn't be done that way.

It's not compassionate to help someone waste their time, honestly. also idk about JT but I thought my response fell under "mild criticism." One's not going to get very far in life if one falls apart under the burden of mild criticism.

It is called a window discrimintor, you can make one with 2 opamps or comparators and an AND gate. One has output high if lower than 1.62035, and the other has output high if higher than 1.5959. Both into the AND gate, and there you are.

1.62035 -- + out ----- Vx ------- - | | ---| | | AND ---- out, high if 1.5959 < input < 1.62035 | ---| --- + | out ---- 1.5959 --- -

PS you can make an AND gate with 2 diodes: + | ----|

Do you realize that the resistors you can buy have values accurate to 5% usually, 1% sometimes, and 0.1% rarely?

Do you realize that there is no way to get accuracy of 1/200th of 1% using those resistors?

0.1% or lower tolerance is easily available on rs-online. here is a 0.1% ht tps://au.rs-online.com/web/p/through-hole-fixed-resistors/1664379/ and ther e are even 0.01% tolerances:

At what budget? If you mean as much precision as your decimals imply, then expect to spend over $10 on semiconductors alone: voltage reference, low offset comparators, precision resistors.

By the way, you're specifying a digital outcome, so "no digital solutions" is self contradictory. :)

Tim

-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website:

%

and th ere are even 0.01% tolerances:

What is the acceptable tolerance of, say, the 1.62035V ?

3 decimal place precision :)

ge

n 5%

%

and there are even 0.01% tolerances:

1 3 decimals so 1.620V