Post by thread:DTMF receiver to telephone line without transforme

Does anyone know how can I connect DTMF receiver (MT8870 for example) to telephone line. I have some circuits but there is transformers. Is it possible to do this without transformer? Thanx in advance. Emil __________________________________________________ Do You Yahoo!? Talk to your friends online with Yahoo! Messenger. http://im.yahoo.com

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 At 09:42 AM 2/25/2000 -0800, Emil Hristov wrote: >Does anyone know how can I connect DTMF receiver >(MT8870 for example) to telephone line. I have some >circuits but there is transformers. Is it possible to >do this without transformer? Depends on what you're doing with it, but in general, that IS the easy way (at least the easy way that also works!) If you're doing anything other than totally isolated, battery or line powered equipment, you need the isolation. You can do it with optoisolators, but that's not a simple project. -----BEGIN PGP SIGNATURE----- Version: PGP for Personal Privacy 5.5.2 iQA/AwUBOLa/coFlGDz1l6VWEQJiggCg29ABdarCa4fPnrrUOaHqAtczuEsAoPqY buC6ucFHwNHKzt1qeJiKnGT6 =tAl0 -----END PGP SIGNATURE-----

a crude simulation of a phone line transformer could be: 220nF ______ o---------o----||----o---|______|-----o--------> | | R 100 | phone | | .---' To the Device line | | | | A | | | | | 5V Zenners R | | R | | V 680 T 2k2 T .---' | | | o---------o----||----o----------------o--------> 220nF

At 09:42 AM 2/25/00 -0800, you wrote: >Does anyone know how can I connect DTMF receiver >(MT8870 for example) to telephone line. I have some >circuits but there is transformers. Is it possible to >do this without transformer? > Check out http://www.hut.fi/Misc/Electronics/circuits/teleinterface.html for all kinds of telephone circuits. - Dan Michaels Oricom Technologies http://www.sni.net/~oricom

In a message dated 2/25/00 12:44:25 PM Eastern Standard Time, spam_OUTe_hristovTakeThisOuTYAHOO.COM writes: > Does anyone know how can I connect DTMF receiver > (MT8870 for example) to telephone line. I have some > circuits but there is transformers. Is it possible to > do this without transformer? > > Thanx in advance. > > Emil Yes it is possible. Motorola MC34014P does a great job. It is not recommended for new designs at this time, meaning that it will be discontinued in the next few months. They also have another one that, I think, is going to replace it. I can't remember the part number but it is maybe MC34018P; not sure. Hope this helps, Max