problems with a cm8880 dtmf decoder
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i am having problems with a cm8880 app kit that i bought from parallax, the
problem i am having is that it dosn't decode all the tones,
the first time i build the circut on a soderless bread bord and all tones
worked except #. my dtmf sorce is a 16 keypad radio, the other thing that
is different is that parallax substituted a resonater insted of a cristal.
the second time i built the same chips on a bread board, my thoughts were
that mabe stray capacitance was throughing off the frequnacey standard.
after building and cleaning the hell out of the board things got worse, now
3,4 and D work intermitently and i cant ever get # to work. I have shielded
the pcb to eleiminate any rf interfreance.
I also tried a 9 v battery across a phone set like the documentation said
but i could not get that to work at all.
any ideas?
Lincoln
problem i am having is that it dosn't decode all the tones,
the first time i build the circut on a soderless bread bord and all tones
worked except #. my dtmf sorce is a 16 keypad radio, the other thing that
is different is that parallax substituted a resonater insted of a cristal.
the second time i built the same chips on a bread board, my thoughts were
that mabe stray capacitance was throughing off the frequnacey standard.
after building and cleaning the hell out of the board things got worse, now
3,4 and D work intermitently and i cant ever get # to work. I have shielded
the pcb to eleiminate any rf interfreance.
I also tried a 9 v battery across a phone set like the documentation said
but i could not get that to work at all.
any ideas?
Lincoln