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Design >> Analog Design >> Opamp circuit need help
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Message started by toma on Jan 14^th, 2010, 7:09am

Title: Opamp circuit need help
Post by toma on Jan 14^th, 2010, 7:09am

Hey.

Im an engineering student, and in need for some help.
Im working on this project, that mainly involves programming of a microprosessor which is more my area than circuit design.

Anyways, i have to prosess a dc signal between -0.5 and 1.7 volts with a freq around 2k hz. The signal comes from piezo electric sensors.

the microprosessor doesent deal with negative voltage, so i need to lift the signal with 1 volt, without masking the original signal to much.

The piezosensor producent says i need a input impedance around 10 mega ohm.

i have been working with proteus isis with some designs of opamp circuits. I created a opamp non inverting adder circuit with resistors in the megaohm area, and another in the kohm area, and the output signal looks good in both circuits. But my university contact person claims i need a capacitor on the signal input.

which totaly messes up the amplifing, which needs to be 1.

I might be going the wrong way about this, couse i have been stuck a long time now. Anyone got any ideas of how i can solve this?

thnx in advance, all help is apreciated.

best regards.

PS: Sry for spelling errors, english is not my first language.

Title: Re: Opamp circuit need help
Post by buddypoor on Jan 14^th, 2010, 7:25am

Hi TOMA,

i have to prosess a dc signal between -0.5 and 1.7 volts with a freq around 2k hz.
What does this mean? DC signal with a frequency of.....???
Please, be more accurat.

As another point, what is/are the supply voltage(s)? Single/dual?

It would be best if you could show us a circuit diagram with all relevant infos (input and output as required).

Title: Re: Opamp circuit need help
Post by toma on Jan 14^th, 2010, 9:04am

yeah lol, can see that was abit confusing sry.

first of all, thnx alot for taking the time, and the quick reply.

Since i dont have to oppurtunity to test my circuit with the true signal, im testing it with a pulse signal thats got a freq on 2k.

the piezo sensors when nothing happens is around 0v , and when applied pressure sends out a signal with max peak around 1.8v before it drops to around -0.5v.
the signal that lasts a couple of ms, before its setled around 0v again.

Im sry i cant give you any more information about the input signal then that, but the output should be the same signal, only 1 volt higher.

the supply voltage is not yet determined, gna create that aswell, but probably will be +- 12 V.

heres two screenshots of the circuits i have created so far. Here i use a +-5 volt suply. Not sure thats what you had in mind.

Sorry if my info isent enough, i should get more exact input info next week. But its rather the principle itself of "lifting" the signal one volt, than exactly determining resistors etc.

You think a opamp circuit is the right way to go?

Again, thnx for your time.

edit: only got one screenshot, the one with hight resistors on input.