Hi.
There is a sample caller id project by sm8223 chip, sm8223 is a FSK/DTMF decoder its ideal for telphone circuits. This project is ok and test by me, its correctly decode recive dtmf/fsk code, but maybe have a problem in detect hang up tel line, for debug you can change value the resistor of input of opto coupler. this circuit is ideal for MT8870 or MT88e43 to make a caller id or signal detector of tel line.
My circuit decode signal by 3 different protocol and send decode data in 1200 baud rate.
If you can see the circuite you can advertent the ring circuit is not used!!!
It is not very hard, Plese see to the circuit of SM8223.
Now see section of ring detector:
The ring circuit is not relevance to decoder circuit !!!, ring circuit is a filter to improve the level signal ring to detect ring signal, that not used for my project.
I use a circuit for detect line of tel for decode hook up or hang up, because bandwith of fsk decoder is 1200Hz to 2200Hz, so frequency of voice is 50Hz to 8KHz, so fsk decoder mistake between sound signal by fsk code, line detector know to micro discard incoming signal when tel line is hookup.
For get Shematic and source code click here.
