Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!wsrcc.com!wolfgang
From: wolfgang@wsrcc.com (Wolfgang S. Rupprecht)
Newsgroups: sci.electronics
Subject: Re: >> WANTED: ScHeMaTiC FoR TeLePhOnE LiNe "In UsE" bLiNkEr
Message-ID: <1991May27.184109.10126@wsrcc.com>
Date: 27 May 91 18:41:09 GMT
References: <76376@eerie.acsu.Buffalo.EDU> <1991May14.122242.15062@rodan.acs.syr.edu> <4647.283a2400@iccgcc.decnet.ab.com>
Distribution: na
Organization: Wolfgang S Rupprecht Computer Consulting, Washington DC.
Lines: 48

>>>     I want to add a phone line-powered L.E.D. blinker on one
>>>     phone which will activate whenever any other phone in the
>>>     house is off-hook.

How about the following circuit I just hacked up?  This circuit has
the following good properties:

        1) takes NO current from the phone line when the phone is on-hook.
                (very important !!!)

        2) takes minimal current (1 ma. max) when the phone is off-hook.
                (not as important - as long as the impedance is a few
                times higher than the other phone on the line.)

	From the advertise a bug as a feature category:

	3) detects ringing also.



                        +---------------+---------o +10v  
                        |               |        
                        Z               |        
                        Z 10k           |  
                        Z               v E   
                        |        B    |/      
                        +-------------|   PNP - 2N2907
                        |             |\              
                        Z               | C           
                        Z 10k           |     
                        Z               Z     
                        |               Z  1 k 
    o--------|<|--------+               Z      
                                        |      
                                        -      
  to phone                              V   LED   
    line                               ---     
                                        |
                                        |
    o-----------------------------------+----------o PS return    
                                                     (not ground !!!)

If you hook it up and it doen't work - reverse the phone leads.

-wolfgang
-- 
Wolfgang Rupprecht    wolfgang@wsrcc.com (or) uunet!wsrcc!wolfgang
Snail Mail Address:   Box 6524, Alexandria, VA 22306-0524