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.

Schematic

Parts

Part	Total Qty.	Description	Substitutions
R1	1	270K 1/4 W Resistor
R2	1	1.5K 1/4 W Resistor
R3	1	68K 1/4 W Resistor
R4	1	33K 1/4 W Resistor
C1	1	0.22uF 150 Volt Capacitor
Q1, Q2	2	2N4954 NPN Transistor
D1	1	1N645 Diode
MISC	1	Wire, Plugs To Match Jacks On Recorder, Board, Phone Plug

Notes

The circuit can be placed anywhere on the phone line, even inside a phone.

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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Comments

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anonymous 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.

anonymous 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.

osmus 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.

Harry 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.

anonymous Telephone Recorder Thursday, September 24, 2009 10:13:23 AM

This Telephone Recorder is fucking rad!

anonymous 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.

sagar 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

navaneeth 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?

antany Telephone Recorder Tuesday, January 22, 2008 12:13:53 PM

where should we connect the inputs (on which phone line)

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anonymous	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.
anonymous	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.
osmus	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.
Harry	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.
anonymous	Telephone Recorder	Thursday, September 24, 2009 10:13:23 AM
This Telephone Recorder is fucking rad!
anonymous	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.
sagar	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
navaneeth	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?
antany	Telephone Recorder	Tuesday, January 22, 2008 12:13:53 PM
where should we connect the inputs (on which phone line)