lairdkb@mentor.cc.purdue.edu (Kyler Laird) (10/05/90)
Well, Radio Shack discontinued one of their neatest chips right when I fried (ring signal) the two I had for a project due soon. Where do I find a 276-1303 or SSI202 or whatever - just as long as it easily decodes DTMF? This must be a common item, but I can't find it locally. Any help will be greatly appreciated. --kyler
cgordon@vpnet.chi.il.us (Gordon Hlavenka) (10/09/90)
After you get this thing replaced, do this:
input ----||---/\/\/\/---+----+------to decoder input
1uF 1.2K _|_ |
\ / ---
V A (Silicon diodes, like 1N4148)
--- /_\
| |
+----+
|
GND
This should block the ring voltage for you... It takes off any DC, does a
current limit (which shouldn't affect sensitivity since the decoder input is
Hi-Z) and then limits the voltages to 1 diode drop -- about .7V
Plenty of signal is left over for the decoder, but ring voltage is reduced
to non-injurious levels.
If you're looking for _any_ DTMF decoder, look for the SC11204 from Sierra.
(Sierra: 408-263-9300)
-----------------------------------------------------
Gordon S. Hlavenka cgordon@vpnet.chi.il.us
Disclaimer: Sierra who? Never heard of 'em!