
Re: Why trig?
Posted:
Apr 1, 1997 11:08 AM


Addressed to: Ray Meester <meesterr@mscd.edu> mathteach@forum.swarthmore.edu
** Reply to note from Ray Meester <meesterr@mscd.edu> Tue, 01 Apr 1997 07:01 0700 (MST)
> Tell the teenages that their touch tone phones work because of trig.
How is it involved?
This much I know: Each row of buttons is assigned one tone frequency. Each column of buttins is assigned one tone frequency.
With made up frequencies, something like this:
300hz 1 2 3 350hz 4 5 6 400hz 7 8 9 450hz * 0 #
5 5 6 0 5 0 0hz 0hz 0hz
So each button has a unique pair of frequencies. A filter (something that has a resonant frequency that matches one of those listed) lets the signal go through if it matches the filters frequency. So two of the filters have an output voltage and the other 6 filters have no output signals.
(Only operators and kids with black boxes have the forth, 650hz, column of buttons, so there are 8 filters, 4 for the rows and 4 for the columns.)
This, at least, is my understanding. My guess is that trig is involved in designing filters, but I've no idea how. Maybe somebody could explain?
************************************************************************ * George Yanos * * GYanos@uic.edu * * 7088484221 * * Fax:6303230924 * ************************************************************************

