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Old 1st April 2011, 07:30 PM   #1
two0 is offline two0  United States
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Question need design help with a phone call recording schematic

RadioShack used to sell a device they called "Wireless Phone Recording Controller" (part 17-855) that would hook up between your phone and headset to record voice conversations. Their design was an active circuit, and required batteries to operate. They've since pulled it from their shelves (for legal reasons, I assume). I've been trying to come up with a way to do this passively, hopefully with just a few resistors. I drew up this schematic, and would like to get some advice on how to make this work, and what the proper resistor values would be. If passive can't be done, can anyone provide a schematic for an active circuit? Thanks.

PS. I'm aware of the laws concerning phone conversation recording. I take down a lot of customer information over the phone at work, and just need to be able to go back occasionally to verify that I heard a piece of information correctly.
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Last edited by two0; 1st April 2011 at 07:36 PM.
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Old 1st April 2011, 10:51 PM   #2
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I'm pretty sure is all you need to do is get the signal off of the handset speaker and you will get your vioce and the parties vioce at the same time. jer
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Old 4th April 2011, 02:55 PM   #3
two0 is offline two0  United States
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Thanks geraldfryjr. If that woks, it would certainly simplify things. I'll give that a try when I get a chance, and post my findings.
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Old 5th April 2011, 06:05 PM   #4
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Years ago radio shack used to sell a pickup coil with suction cup on it that you would just stick on the handset and it would plug into the microphone input of a portable cassette recorder.

Recently I saw a device that plugs into to a cellphone and records the conversation in a MP3 format. jer
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Old 5th April 2011, 09:40 PM   #5
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When you use the term "phone" I asume you mean telephone.
The telephone line is a 600 Ohm balanced circuit with DC and a bunch of other stuff riding on the line when the phone is off-hook. There are very strict regulations as to the loading of that line. Any imbalance caused by your equipment will be quickly noticed by the service provider.
If you do record a conversation you are required, by most laws, to send a "supervisory" tone the other party can hear and therefore know that the call is recorded.
But the circuit in itself is dead simple...E
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Old 5th April 2011, 10:36 PM   #6
tomchr is offline tomchr  United States
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In many places - the US included - you also need the permission of all parties to record. What tends to happen is that the interviewer will ask off the record, "is it OK if I record this conversation?". If the answer is yes, then the recording is started and the interviewer will repeat the question and have the permission recorded.

~Tom
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Old 5th April 2011, 10:55 PM   #7
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Laws vary from state to state in the US. Some require both parties to be aware of the recording, some require just one. If neither knows, that's illegal phone tapping, without judicial authority of course. If two0 just wants a work aid, I for one am not going to alert the Feds.
The type of phone used makes the most difference for the final circuit, as the different methods suggested above point out.
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Old 6th April 2011, 08:43 PM   #8
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Here is some info for those interested in knowing more. jer


Wiretapping and Eavesdropping on Telephone Calls | Privacy Rights Clearinghouse
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Old 7th April 2011, 06:38 PM   #9
two0 is offline two0  United States
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perhaps I wasn't clear enough in my first post, so let me clarify here. Most wireless phones these days have a 2.5mm jack that lets you plug in a headset for hands free calling (see attached). Most cell phones have this jack also, or at least some type of adapter that gets you to the standard 2.5mm headset jack. That headset jack is where I want to tap into the audio of both sides of the conversation.

What I'm trying to make is make a Y adapter with a male 2.5mm that will plug into the jack on the phone, then splits into a 2.5mm female that the actual headset plugs into, and a male 3.5 mono plug that plugs into the recorder's mic in.
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Old 7th April 2011, 10:03 PM   #10
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The phone-to-headset part of the Y connector can just be straight-thru, so I don't think you need the bottom two 220-ohm resistors. The other resistors provide some isolation to the recorder, but I think actual values depend on the sensitivity of the recorder input. Your values can be starting point, but they may need to be increased or decreased for satisfactory recording levels. Hope this helps you.
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