Detecting a telephone RING

(Circuits -> Telephone)
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From: unknow

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  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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