Telephone Recorder

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This nifty little circuit lets you record your phone conversations automatically. The device connects to the phone line, your tape recorder's microphone input, and the recorder's remote control jack. It senses the voltage in the phone line and begins recording when the line drops to 5 volts or less.


This is the schematic of the Telephone Recorder


Total Qty.
R11270K 1/4 W Resistor
R211.5K 1/4 W Resistor
R3168K 1/4 W Resistor
R4133K 1/4 W Resistor
C110.22uF 150 Volt Capacitor
Q1, Q222N4954 NPN Transistor
D111N645 Diode
MISC1Wire, Plugs To Match Jacks On Recorder, Board, Phone Plug


  1. The circuit can be placed anywhere on the phone line, even inside a phone.
  2. Some countries or states require you to notify anyone you are talking to that the conversation is being recorded. Most recoders do this with a beep-beep. Also, you may have to get permission from the phone company before you connect anything to their lines.

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Add A Comment

Telephone Recorder
Wednesday, November 23, 2022 3:24:01 AM
I agree with the previous comment. An isolation transformer in the recorder Mic output is necessary. Also, a small bridge rectifier placed in the telephone input serves to iron out any reverse polarity issues. With those two modifications, this circuit works very well and is far simpler than most. Substitute freely--the switch mechanism is not that fussy. Thanks.
Telephone Recorder
Saturday, April 27, 2013 11:57:01 PM
If you connect any expensive recording device to a telephone line without complete DC isolaation you risk burning out componnets on the device, not really woth wrecking a PC or its soundchip just to save on a cheap audio isolation transformer. Nowadays PSTN lines are often fitted with incorrect polarity too... without isolation you will lilkely get a nasty hum if you are fortunate or silence of a fried motherboard if you are not so fortunate.
Telephone Recorder
Monday, March 21, 2011 7:11:15 PM
wihout a line isolation with transformer its a bad idea to plug your mic to phone.
Telephone Recorder
Friday, April 02, 2010 9:52:42 AM
Can somebody mail me the circuit details. I need this to record my meeting and will help me plan my communication/actions better. Currently I use the speaker phone and have problem with noise when I speak into it.
Telephone Recorder
Thursday, September 24, 2009 10:13:23 AM
This Telephone Recorder is fucking rad!
Telephone Recorder
Friday, October 31, 2008 12:39:15 AM
its a nice circuit idea. Simple one. Nothing new though.
Rao Waseem
Telephone Recorder
Thursday, May 08, 2008 3:40:12 AM
this is very useful project.i liked it very much if u can any comments u can mail me.
Telephone Recorder
Thursday, February 28, 2008 3:57:06 AM
if u dont mind pls mail me the complete info,block diagram,circuit diagram&major advantages ,applications of this project which helps me in doing my mini project
Telephone Recorder
Tuesday, February 19, 2008 6:40:26 AM
would youmind pls mail me the complete info,block diagram,circuit diagram&major advantages ,applications of this project which helps me in doing my mini project. what is remote control jack stands here for?
Telephone Recorder
Tuesday, January 22, 2008 12:13:53 PM
where should we connect the inputs (on which phone line)
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