Re: gEDA-user: Simple LM741 Op-Amp Example

[Michael B Allen <ioplex@xxxxxxxxx>]

On Sun, May 17, 2009 at 4:08 AM, Gabriel Paubert <paubert@xxxxxxx> wrote:
> On Sun, May 17, 2009 at 12:29:52AM -0400, Michael B Allen wrote:
>> Hi,
>>
>> I'm just paying around but I'm trying to do a simple LM741 Op-Amp
>> simulation. Here is my schematic:
>>
>>   http://207.192.69.113/~miallen/lm741.pdf
>>
>
> It can't work, but I have difficulty guessing what you want to do.
> If you want an inverting amplifier, you have to put a resistor in
> series with V2 (between V2 and the inverting inputof the opamp),
> and probably change the DC voltage of V2 to 1/2 V1.
>
> IOW, the inverting input is used for the feedback, but if you connect
> it to a voltage source with zero impedance, it can't do its work.

Hi Gabriel,

I got the simulation to work. Aside from the missing resistor my main
issue seemed to be just figuring out how to handle the dual power
supply. Here's the working version (with full netlist):

  http://207.192.69.113/~miallen/lm741_2.pdf

>> Is my voltage divider wrong? How do I get -4.5 and +4.5 to Vss and Vcc
>> respectively?
>
> By using 2 voltage sources of 4.5V in series and using the common point
> as a reference?

That's what I ended up doing. I wanted to see if I could get it to
work with one battery but it seems doing a virtual ground with two
resistors is not as simple as I thought. For now I'm just going to use
two batteries since this is really just a practice run.

The next objective is to use a TL082 "Dual BiFET" op amp that I also
got from Radio Shack to make a buffer circuit for interfacing with the
mic in and output of my laptop sound card [1]. The TL082 also needs a
virtual ground. This page has very interesting information about
virtual ground circuits:

  http://tangentsoft.net/elec/vgrounds.html

It sounds like I'll need to get a "rail splitter" like the TLE2426.

Thanks,
Mike

[1] Although depending on how that goes I might have to try the
PicoScope 2203 PC oscilloscope which can take regular BNC probes and
has a signal generator.

-- 
Michael B Allen
Java Active Directory Integration
http://www.ioplex.com/


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