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I am trying to find a message waiting indicator (MWI) circuit that I can connect to a phone line and have an LED glow or flash to indicate that there is a message on the telephone companies voice mail system. I (believe I) need to detect the stuttered dial tone that the phone company uses to indicate a message is waiting. I have seen this function on several phone units, but as yet have been unable to find a circuit or even functional description. An internet search results in all sorts of phones for sale with the function. I eventually would like to build a small box that plugs into my wall jack (rj45 - 4 individual lines) and display an LED for each line. Any pointers would be greatly appreciated.<p>Thanx

found a little bit more info - I am looking to implement a visual message waiting indicator (vmwi) prefereably with the ability to detect either the FSK signal or the stutter dial tone.<p>Any links to circuits or chip specs appreciated.

dig though here - there ought to be some ideas to draw on.
http://www.discovercircuits.com/T/telephone.htm<p>[ March 07, 2005: Message edited by: philba ]</p>

As far as I know, you don't get any sort of dial tone while the phone is on-hook, so I doubt if this is possible.

Thanks philba - tried Discover Circuits - no luck yet. I have found spec sheets for "Zarlink MT88E39" and "MXCOM CMX673" whose application noted indicate a 2 chip scenario - one chip handling the FSK the other chip takes the line off-hook and "listens" for the stutter tone, then goed back on-hook. I guess my original thought bias was going to be some sort of simple detector circuit. I wonder if anyone might have ideas on working with any of these chips - maybe with a microcontroller.