Path: utzoo!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!sco!deanr
From: deanr@sco.COM (Dean Reece)
Newsgroups: sci.electronics
Subject: Re: Wanted: Phone-in-use Indicator
Message-ID: <4176@scolex.sco.COM>
Date: 19 Dec 89 23:19:27 GMT
References: <6375@nigel.udel.EDU> <1989Dec18.101522.20175@santra.uucp> <4174@scolex.sco.COM>
Sender: news@sco.COM
Reply-To: deanr@sco.COM (Dean Reece)
Organization: The Santa Cruz Operation, Inc.
Lines: 64


In article <4174@scolex.sco.COM> I write:
>
>In sci.electronics neumann@udel.edu (Brian R. Neumann) writes:
>>
>>Does anyone know of any simple circuit I could build or of any device
>>that I could by to show when the phone is in use?
>
>Sure, I built one into my phone, and it works great.  The schematic is
>available on page 668 of "The GIANT Handbook pf Electronic Circuits"
>published by TAB books, ISBN= 0-8306-9673-3 in hardback, or ...-9662-8
>in paperback
>
>It needs a 6 volt (or 5 volt) external supply.

I meant that the circuit needs 5 volts, not the book :-)  Anyway, I thought I
would try to post the schematic.  The branch of the circuit that contains
C1, C2 & R5, R6 is only used as a passive tap. (So you can record the line
when the rest of the circuit says 'off hook'.  It can be removed if not needed.
If used, it can directly drive a microphone input to a portable recoreder.

The Output of Q2 completes a path to ground when the phone lines gives an off
hook reading.  This can drive a relay (for a tape recorder motor) or an LED.
Be sure to include a current limiting resistor if an LED is used.  Also, D1
may be ommited if a non-inductive load is used (Relays and incandescent (sp?)
lamps are inductive)

The LED thingy like this that I made for my phone flashes nicely when the phone
rings (at the 20..25 Hz ring freq), so I can turn the ringer off, and still
get silent ring indication (a feature, not a bug)

Well, its not exactly postscript(tm), but if you stand back and squint, you'll
get the idea.

      R5
<----+^v+                       +----------+--------* +6vdc (I use 5 volts)
   R6>  |                       |        D1_
     <  |                     R3>          ^          ___
<----+  |                       <          +--------> Out
     |  |                       | R8   Q2|/
   C1=C2=                       +-^v-+---|
     |  |   R1 BR1__        Q1|/     |   |\v
*----+------v^---|  |--+--+---|    R4>     |
        |        |~+|R7<C3L   |\v    <     |
        |   R2   |~-|  >  T     |    |     |
*-------+---v^---|__|--+--+-----+----+-----+--------* Ground
                       |_
                      ///

R1, R2	2.2M				Reproduced (kind of) without
R3, R4	470K				permission.   Copyright 1980
R5	470				TAB BOOKS Inc.
R6	100
R7	100K
R8	220K
C1, C2	0.01uf, 100V
C3	1.0 uf
BR1	Full wave Bridge Rectifier, about 200 VDC (or higher)
D1	HEP R0052 (I use 1N400*)
Q1, Q1	HEP S9100 -or- NTE-172a
 ______________________________________________________________________
| Dean Reece     Member Technical Staff |"The flames are all long gone |
| The Santa Cruz Operation 408/458-1422 | but the pain lingers on"     |
|___________deanr@sco.com_______________|___________________Pink_Floyd_|