[sdiy] Impedance / equivalent resistance calculation

[Philippe DERENNE]

Hi Bert,

Brutele is providing TV and Internet near Brussels-South Airport as well ;-)
I'm near Charleroi... and I'm glad to see that I'm not the only guy from
Belgium on this list :o)

Phil.

----- Original Message -----
From: "Bert Schiettecatte" <bert at percussa.com>
To: "'Roman'" <modular at go2.pl>; <synth-diy at dropmix.xs4all.nl>
Sent: Saturday, September 03, 2005 2:19 AM
Subject: RE: [sdiy] Impedance / equivalent resistance calculation


> Hi,
>
> > your DC impedance at IRIN1 is parallel connection of IR5 and
> > IR9, that's 750ohms. If you expect to detect the light at
> > frequency highier than, say, 40Hz (twice corner frequency of
> > filter made of IR5,9, IC9), cou could consider the cap as
> > short. Your node with IR1 and IQ1 has equivalent resistance
> > of 690 to 2.1k (again, parallel of IQ1 and IR1 in light and
> > dark), so overal AC impedance is more or less (690-2100)||750
> > = 360 - 550 ohms
>
> That's what I thought too but I was not sure I could look at
> The 10uF cap as a 'short'.
>
> Now, I do understand that IC9 and IR9 are forming a high-pass
> Filter, and that IC1 and the equivalent resistance before it
> Will form a low-pass filter. Are there any other filters I am
> Missing here? I don't see how IR5 is involved in a filter.
>
> Thanks,
> Bert.
>