On Wed, Jan 26, 2011 at 12:21 AM, RussellMc <apptechnz@gmail.com> wrote:

> Or, not if you want it to work*.
>
> However, if you use an LM324 for the opamp then using an electrolytic
> there, or a small brick, probably won't make a vast difference to the
> usefulness of the result.   :-(
>
> * Even that is not 103% true. It may work after a fashion but
> operation will be further degraded in a circuit that is already below
> optimum as designed (using LF353) and made worse again with LM324.
>
> BUT the value of C1 is not overly crucial 9probably). Using say 10 x
> 0.1 uF non polarised would probably be good enough (more lead
> inductance) and anything in the 0.1 - 4.7 uF range may be OK - maybe
> even outside that range.
>
> But, as olin notes, the circuit lives and dies on its balance
> properties, once you have an opamp that does justice to the need, and
> imbalance will destroy common mode rejection in an environment where
> common mode may be >> signal.
>
> There are some jobs where you need to come withing spitting distance
> of the correct solution to make it worth doing at all. This is one of
> them. Use of very or very very  inferior opamps, unbalanced resistors
> and out ofspec cap values is going to make life interesting.
>

I'm not saying that I don't believe you guys, but the fact that the guy got
good results (http://www.eng.utah.edu/~jnguyen/ecg/bigecg.gif) motivates me
to continue with this schemtic. He used 5% resistors, even.
--=20
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