brendan@otc.otca.oz (Brendan Jones) (02/19/91)
There have been a few calls recently in sci.electronics for phone in use
circuits (ie a circuit that lights a LED when an extension phone is off
hook).
Following are two circuits I archived some time ago from sci.electronics.
The first appears pretty complete and requires an external 5V power supply.
The second seems to be a loop current trap that enables you to move from
one extension phone to another without leaving the first phone off hook.
I don't know how well either of these circuits work as I haven't actually
built them.
---8<-----8<-----8<-----8<-----8<-----8<-----8<-----8<-----8<-----8<-----8<---
PHONE IN USE CIRCUIT
--------------------
I thought I would try to post the schematic. This circuit requires a separate
5 volt supply. 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
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From: barber@beowulf.ucsd.edu (Terri Barber)
Newsgroups: sci.electronics
Subject: Re: How Do I Make a Phone In-Use Light?
Date: 2 Jul 90 21:30:58 GMT
Sender: news@sdcc6.ucsd.edu
Organization: CSE Dept., U. C. San Diego
Lines: 40
In article <4633@milton.u.washington.edu> wiml@milton.u.washington.edu (William Lewis) writes:
>In article <904@eplunix.UUCP> raoul@eplunix.UUCP (Nico Garcia) writes:
>>In article <1558@yenta.alb.nm.us>, dt@yenta.alb.nm.us (David B. Thomas) writes:
>>> Another neat phone circuit (VERY simple) uses an scr, a couple of resistors
>>> and a button. If you wish to switch phones, you hold in the button (gating
>>> the scr), then hang up. The scr maintains loop current. An led could be
>>
>>Ummm, can you post this one? Enough of us do occasional phone hacking that
>>I'd like one as well.
>
>
> I second that. It would be extremely useful around here ...
Okay, let's see if I can remember how to do it (I didn't post the original,
I just want to stick my $.02 in....
Please excuse the ascii graphics....
-------------------+------+----
| |
| /
| / momentary switch
| |
| /
| \ 1200 Ohm
| /
-----____|
/ \
/___\ SCR
|
/
\ 600 Ohm
/
| ^^
----- //
/ \ //
/___\ LED
|
|
-------------------+---------
---8<-----8<-----8<-----8<-----8<-----8<-----8<-----8<-----8<-----8<-----8<---
I hope this helps...
--
Brendan Jones | ACSnet: brendan@otc.otca.oz.au | What does
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