> > Can you please explain how you deduced those two frequencies.
>
> This is very basic electronics:

It is.

> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 1
> Frequency =3D ---------------------------
> =A0 =A0 =A0 =A0 =A0 =A02 Pi Resistance Capacitance

In isolation, yes.

           Given Tc =3D time Constant =3D R x C.

I note that there is  a factor of about 6 (and slightly different in
each case, mainly due to rounding) between 1/Tc and the frequencies
that you stated. ie ~=3D 2Pi.

In what is essentially a passive 2 stage (one pole, one zero) RC
filter the second stage will load the first somewhat, BUT the biggest
area of 'debate' is where the 3 dB corner frequency lies compared to
the simplistic case.

At the corner frequency of the first RC stage the second 10 uF has an
impedance (of course) equal (in magnitude) to the resistance of R1, so
C1 is loaded with a series load of 148k capacitive in series with 320k
resistive. This loading is non trivial and will skew the result.

In this case the HP & LP frequencies are well enough out of desired
range (depending on what heart is being measured :-) ) and excessively
'tight' that the difference between simplistic and actual are more of
academic than actual interest.

I genuinely wont suggest that your answer was sloppy, as I don't think
that real precision is required when giving examples like this BUT I
make the point (no doubt rejected :-) ) that if somebody else had done
that, then 'sloppy" would have been the least of the epithets that you
would have used.
You can say that the difference is not important in this case, and I'd
agree, and isn't the point of the exercise, and I'd agree, and ... and
I'd probably agree :-) - but the point is that you need to allow some
"sloppiness to others in equivalent circumstances. No?



           Russell

--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.