ive constructed the circuit exactly like the one here. i have'nt assemble the relay parts yet bcoz i wanted to make sure the dtmf decoder n the few main ics are working. first i proceed to check for the required output frm the decoder by using the input frm the telephone line paralel to the telephone instrument. i tried to press for diffrnt keys to get the desired output but unfortunately all attempts have been a failure so far.
i am in a despair right now because i dont know wat izzit tat is wrong. im sure the circuits are connected properly. even my lecturer is not sure wat the problem is.
can some1 shed som light on me???
thank you vr much..
Check the simple things first. Battery and ground in all the right points at each IC.
Next, trouble shoot the problem by using the half-split method. Go into the 154 decoder IC inputs, simulate an input and check for the desired output. If that is OK you know problem is in the DTMF decoder half of the circuit, if not OK you know it is in decoder or downstream from there.
Dialtone