Record landline telephone calls with a mobile phone.

This video shows you how you can use a mobile phone to record with full safety isolation from the telephone line.
Most telephone adaptors available on the market do not have full galvanic isolation, they simply use a couple of capacitors, and this can affect the phone line safety and quality of the recording.
My design improves the isolation by using a 1:1 transformer salvaged from and old fax-modem card. As well as having excellent isolation, it provides high quality sound recording. As the adapter is fully isolated, the phone can be permanently on charge without any problems.
The cable between the adapter and mobile phone was taken from an old hands-free mic/headset, and should have a 4 pole jack plug. The other end has a 3 pole stereo jack plug with L and R channels joined together.
A recent comment reminded me that the mobile phone jack usually has the microphone connected to the sleeve (first ring) and the ground to the second ring. Check your phone as these may be reversed. This link may help thecablesland....
You can use any mobile phone that has a headphone socket or headphone adapter. I re-purposed my old Galaxy S4 as it provides a recording timestamp and the ability to use a meaningful filename. As an added bonus, the phone may be connected to wifi and the audio files accessed via the network.
I have made the schematic and suggested layout available here -
drive.google.c...
Your comments will be welcome!

[@simonmcguire1988]

Well made Richard :) reminds me of the big Clive channel on youtube

[@andrew_langner]

liked, commented, and "smashed" that subscribe button...

[@captmohelsaadany6751]

Well done 👏👌

[@bulletstrongholder644]

Great idea but i guess the first ring is mic and the second one is ground

[@richardlangner]

Thank you very much for your comment. Indeed the sleeve is the microphone connection on the Samsung S4 which I used here, and next ring is ground.
But be aware that it is reversed on some phones, so always check first. I have updated the description, thanks again!
See this link
help.longtailproducts.com/hc/en-us/articles/207970396-Smartphone-Headset-Standards-Apple-iPhone-AHJ-CTIA-OMTP

[@hamzakaose7712]

I want this gadget

[@richardlangner]

I'm glad you like it. My schematic and suggested PCB layout are here drive.google.com/file/d/1qoD6K_yVWtq31sW3qaElEONbOBO7mOBT/view?usp=sharing
Please let me know how you get on.
And click 'like'!

[@bulletstrongholder644]

I tried this the voice from line is excellent but cant hear voice from cellphone

[@richardlangner]

To hear playback from the phone you need to disconnect the jack plug, as the phone thinks a headset is plugged in and mutes the speaker.

[@bulletstrongholder644]

@@richardlangner thanks for your response my problem is that i can hear my voice only in playback but cant hear the voice from the other phone

[@richardlangner]

@@bulletstrongholder644 It sounds like your voice is only being picked up by your phone's microphone. Plugging the jack into the phone should switch it to external microphone. Try plugging in a normal headset to see if the phone actually switches to the headset's mic. In my schematic the 2k2 resistor signals to the phone that a headset and mic are connected (just a few ohms would indicate it's headphones only, and no mic). Also check your wiring. Let me know how you get on.

[@richardlangner]

To clarify, ensure the mono-jack plug on the interface is wired such that the sleeve and tip are connected properly. With the mono-jack plugged into the recording interface, check other end (the phone end, when disconnected from the phone) of the lead - it should read 2k~-4k between the ground and mic connections (first and second ring of the 4 ring plug). If you use a stereojack socket on the interface instead of a mono-jack, it's the same test - ensure the the phone end sees the 2k-4k which should enable external mic.

[@bulletstrongholder644]

@@richardlangner thanks for your help i really appreciate it, i guess there were multiple issues with my board here are my guesses :
1.transformer was faulty or was not 1:1
2.isolation capacitor was too low so it wouldn'T allow low frquencies
3.circuit resistance was too high
I mixed up your idea and electrobooms idea and a commercial phone recorder protection part and made a new circuit it works really well and also protects phone from overvoltage using 2x9 volt zener diodes in series with each other and in paralled with phone recorder
I would prefer adding isolation transformer but for 2 reasons i didn't/couldn't one was that i didnt know the turn ration of my transformers in hand second was that i guess the self resistance was too high it would block some high frequencies from transmission,
Thanks for your videos keep up the good work
The funny part is i'm year 4 pharmacy student and i do these electronic projects as a hobby

[@captmohelsaadany6751]

R1& R2 please

[@richardlangner]

My schematic and suggested PCB layout are here drive.google.com/file/d/1qoD6K_yVWtq31sW3qaElEONbOBO7mOBT/view?usp=sharing

[@captmohelsaadany6751]

@@richardlangner
Thanks for your cooperation 🙏🤗