23rd 2005f November, 2005

Simple Skype VoIP analog adapter

by @ 11:25. Filed under

Skype/VoIP phone adapter

If you have questions – my contacts are:

Pictures on the last page

or USB version (you don’t need external or battery supply)

It’s a very cheap Skype/VoIP interface to your wired or wireless phone.

Just imagine: You can walk with your wireless phone chatting with Skype friends for free, you can make free call to your mom if she is connected to the Internet. You can make your telephone network with servises, voicemail, etc and chat there using your old phone. Skype wireless phones are expensive, VoIP adapters cost ~$60, but you can make it for free if your have details.. from old TV, Radio or other electronics.

You can use such variants as:

1. Using your own PBX (Computer-based telephone station).

Old PC computer as server in your basement and wired/wireless phone.

Software: Windows XP + VMware (running Asterisk@Home 2) + X-Lite softphone + this interface + wired/wireless phone.



2. Using Skype

PC + Skype + this interface + wired/wireless phone.



3. Using X-Lite softphone

PC+ X-Lite + this interface + wired/wireless phone.



1st variant: Using your own PBX (Computer-based telephone station).

You need:

Windows, VMware, Asterisk@Home,Chat-Cord@DialerXT (1.1.0), X-Lite ( 2.0.1103a)

  1. Make new virtual machine in VMware->Typical->Linux->Give a name for example A@H2-> Next, next, next…
  2. Double click on CD-ROM in Properties of this Virtual Machine, choose Use ISO Image, choose your downloaded Asterisk@home iso.
  3. Run virtual machine, clicking Play button.
  4. Asterisk@Home automatically installs. Default account is root, password is password
  5. When you log in, you will see your IP address or type ifconfig.
  6. You can access there using browser, for example AMP account is maint and password is password
  7. Make SIP account in sip.conf for your softphone X-Lite (http://your.server.ip -> Asterisk Management Portal (AMP) ->Maintenance -> Config Edit -> sip.conf and insert this:

    callerid="Your Name "

    201 is your new number, secret = 201 is your password. You can add friend to your network using same things. OK, click Update, click /etc/asterisk at top to return to folder

  8. Make extension for your softphone X-Lite in extensions.conf
  9. ;<201>
    exten => 201,1,Ringing
    exten => 201,2,Dial(SIP/201,40)
    exten => 201,3,Voicemail(u${EXTEN})
    exten => 201,4,Hangup
    exten => 201,102,Voicemail(b${EXTEN})
    exten => 201,103,Hangup

  10. Install and run your X-Lite, in properties put your username and password what you have entered below, SIP Proxy IP. Make sure that it works.
  11. Now Xlite can use your VoIP server for making calls to your friends
  12. Connect your home-made adapter to your Mic input and Speaker out and to your wired/wireless phone
  13. Install and configure Chat-Cord@DialerXT. Now when it is calibrated you can dial and speak using your wired/wireless phone.
  14. Enjoy it :)

2nd variant: Using Skype

You need:

Windows, Skype, Chat-Cord@DialerSK (2.1.0)

  1. Connect your home-made adapter to your Mic input and Speaker out and to your wired/wireless phone
  2. Install and configure Chat-Cord@DialerSK. Now when it is calibrated you can dial and speak using your wired/wireless phone.
  3. Enjoy :)

3rd variant: Using X-Lite softphone

You need:

Windows, Chat-Cord@DialerXT (1.1.0), X-Lite ( 2.0.1103a)

  1. Connect your home-made adapter to your Mic input and Speaker out and to your wired/wireless phone
  2. Install and configure Chat-Cord@DialerXT. Now when it is calibrated you can dial and speak using your wired/wireless phone.
  3. Enjoy :)


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This article has been reposted with the permission of the author.
The original article can be found here

80 Responses to “Simple Skype VoIP analog adapter”

  1. Patricio Campos Says:

    Thanks for the information I did mio asks when receipt a call of skype must sound the bell of the telefonico apparatus? . for that software I must install not to be listened to when I use I telephone? Install the software of the adapter but it does not recognize the keyboard to me that can be.

    Santiago de Chile

    Gracias por la informacion la hice el mio pregunta cuando recibo una llamada de skype debe sonar la campanilla del aparato telefonico ?? . para esto que software debo instalar No me escuchar cuando utilizo el telefono ?? Instale el software del adaptador pero no me reconoce el teclado que puede ser.

    Santiago de Chile

  2. jess Says:

    sir I try to connect a 12 volts direct to power supply of my pc instead of
    9v battereis is not workig it is possible to work my analog phone pls. help me.

    if you have video guide how to assemble un analogphone for skype pls send me to .Thank you very much

  3. Chris J. Says:

    jess: If it only works with a battery (for some people that’s the only way to get it to work) then I would do just that. Use a battery and skip the usb / 12v solution.
    There’s no video guide but the information in the article should be enough for you to understand how to make it.

  4. Demon Says:

    AFAIK, shield contacts (mic&spk out) are connected together in the sound card? Then what is the function of 500 Ohm resistor, it’s contacts are connected throu the sound card … And what does the right picture (2 jacks) mean? What jack’s contacts must be used?

  5. Bob Says:

    I tried this circuit, and it works like a charm. Assembled two of them, for two diferent phones, and the sound was really cheasy in one of them, but cristal clear in the other one. Nevertheless, what’s up with the 500 ohm pot, it doesn’t make any difference when you adjust it, so on the second circuit i just replaced it with a 400-something OHM resistor. PS, i integrated the circuits into the bases of the phones, and used power from their powersupplies, witch leaves me with only two cables sticking out the back and into my PC.
    Gonna try to take some shots later on, but my camera just died, R.I.P.

  6. Gori Says:


    Resistors : 100 ohms – how many watts ? 0.5 watt ?
    Rheostat : 500 ohms – how many watts ? is wattage relevent here ?
    Capacitors : 3.3 uf – how many volts ? what are the maximum and minimum permissable values ?

    If i am unable to get non-polarised capacitors, how do i deal with the polarisation ?



  7. avig Says:

    can you explain me please what it mean usb1 + usb2. isn’t it the same ?

  8. eviltwin Says:


    to “transform” 5 V to 10 V. a phone needs at least 9 V to work.

    5V + 5V = 10 V simple, huh?

    but I have a BIG question: Probably the same as Gori’s)

    Specs to all the components?

    capacitors: what kind?

    resistors: how many watts? etc.

    and if someone would make a a working pack with all the components, i would buy it. (christmas- present, see?)

  9. Iftikhar Ahmad Says:

    I have build the adapter and found it working satisfactory. Used the following.
    1. Old rotary dial phone (no active components)
    2. 100 ohm Resistors used 1Watt type (1/2 watts are ok)
    3. Large Carbon type 500 ohm variable resistance is ok. I set it in the middle position about 250 ohms.
    4. Capacitors are 3.3uf/25 volt Bipolar type (these are small).
    5. It worked ok with 9Volt battery but later replaced with
    an old mobile (cellphone) adapter rated at 11 volts.
    (any 9v to 12v type is ok)
    (if you use this type of adapter then place 1000Uf/25 volt capacitor to smooth the power supply) It seems convenient/efficient solution instead of USB type.

  10. andrew Says:

    I think it will be possible to use this adapter with existing phone line and use its power(48VDC) instead battery. I can use old’s modem board with phone connectors, first use to connect phone, second to connect phone line. Can someone help me to select wright components for such configuration?

  11. Huy Says:

    Can you explain how to wire microphone and speaker out to the circuit? I almost complete this project accept these parts. Thanks.

  12. tamir Says:

    using Iftikhar Ahmad list, ive builed the cuircet but all i got was loopback on the phone,
    my guess is that the mic/spkr are not connected correctly on my board

    on mic connection ===|==|==>
    ive connected ^ ^
    the middle and end tip | |

    on spk connection ===|==|==>
    ive connected ^ ^
    the base and end | |

    any suggestions ?

  13. Chris J. Says:

    tamir: It sounds to me that there’s something else wrong then the connectors, so check your circuit again. Regarding the mic connection, you can try to connect it as you’ve connected the speaker connector. That’s how I did it.

  14. tamir Says:

    Thanx for the tip Chris
    I am really new in building electric stuff so its figures youre right but
    I have checked the diagram and the board and couldn’t find anything wrong
    Could you shed some light on the diagram ?
    I tried switching the capacetors connection direction but it didn’t got me any forther,
    I used your tip on the mic/spk connection as follows:
    The mic is connected using a sterio connector the base and middle segment are connected to the
    board while the end tip (white usally) is not connected at all (is there any diffference wich direction ?)
    The spk is connected also using a sterio connector and the base and middle segment
    are conneted to the board and here also the end tip isn’t connected.
    still all i get when i plug the board is a loopback on the phone i can hear myself speak but nothing is
    is identified on my PC (iv’e tryed MS-recorder for mic check and playing an mp3 for spkr check)
    HELP Please

  15. eviltwin Says:

    Try EVErY posibillity with the jacks maybe?

    the jack settings are for MONO only so… if you want stereo phone out then you need to connect left and right at the same line logically.

    Have ordered the parts now! Weee!

    Pictures on the settings will be delivered as soon as get finish! (using the easy way – my server with skype and the software Chris released on the other skype – pstn hack)

    btw the adapter will be putted INSIDE the pc case, with a rj 11 plug out as a normal card!

    nifty eh?

  16. Iftikhar Ahmad Says:

    Ref tamir post,If using stereo plugs and cables for mic/spkr, at the adapter end, the ground wire goes to the screen of sockets, tip and middle points are looped and connected to other connection.You can use multimeter to verify the connections.

  17. Alan Says:

    I suspect that the circuit takes more current than a single USB port is able to supply, hence the second USB port (?)

    Rather than tying up two USB ports, a quality AC/DC 9V adapter would probably work just as well, and leave your USB ports opened for other purposes.


  18. tamir Says:

    got it to work here are the settings (from a eletronic-newbee)
    1. the capacitors are direction oriented – hence you must connect them on the right polarity
    the (-) is marked on the capacetor by a gray band at one side
    2. the phone jack is to direction oriented make shure the right pin goes to the right whire
    3. the mic connection are as followes: middle segment to one whire and tip segment to th other (orientionless)
    4. the speaker connection is as follows: base segment to one whire and middle+tip to the other (alsow orientionless)
    5. iv’e placed all the cuircit on a board and put it into an old logitech-mouse i had laying around for a case …pictures will follow soon


  19. jacktr Says:

    if my phone does not need a power supply what do i need to build an adaptor,

  20. Eviltwin Says:

    the battery must work as an amplifier, i think

    so i’d perfer using a battery instead of the usb ports, because then you’ll have one noise source less 😛


    two usb’s for AMPLIFYING TO 10 VOLTS! 5 + 5 = 10. serial wired, does that say something to you?

  21. Carlossp Says:

    I’ve just finished to assembly my interface.
    It is working perfectly but the sound is a little bit low and the other side also complained about the volume low.
    I think that this is normal using a resistive bridge, only using a transformer the volume will be perfect.
    Any way I am very satisfied with the circuit.
    Very good.


  22. Hannibal Says:

    I have the same experience with the sound. Can anybody tell me how to solve this?

  23. Daniel Foo Says:

    Hi Chris, this circuit really works! I tried it on my wireless existing phone and incoming calls made using skype
    sounds clear and totally lack of background noise, except it sounds faint somewhat from the calling party.

  24. john Says:

    Just connect a simple lm324 op amp ( or simple single stage transistor amp at the speaker end. Amplification should be between X5 and X10. It’s that simple and it works.

  25. Daniel Foo Says:

    Anybody can come out with a ringing tone circuit to notify when skype phone rings? I think that would be cool.

  26. Arios Says:

    Ok. Guys! Look at this circuit. It’s phone rings.

  27. Fergyc Says:

    why not use an adsl filter as a case???

  28. Fergyc Says:

    and can you use a spare mobile phone

  29. Daniel Foo Says:

    Guys, anybody tried gettting it work on a mobile phone? I mean change the cable that plug to RJ11 to hook up to a mobile phone instead?

  30. Greg N Says:

    The two USB connectors are wired in parallel, so 5+5 =5 volts, not 10. Does that say something to you? I hope so.
    Anyway, USB lines can be very noisy. A cheap 6 volt lantern battery from the supermarket won’t generate noise and will last for a very long time.
    Also, the purpose of the 500 ohm variable resistor is to adjust the load impedance to 600 ohms, as seen by the phone. It can’t do this if it is shorted out by the microphone ground, as it is in the diagram and as pointed out by other readers already. Obviously the diagram was copied incorrectly. The microphone ground should be connected to the same place as the speaker ground, not to the RJ12 socket*. In that case the circuit will work as intended.
    * RJ12=phone socket. RJ11=handset socket, slightly narrower. Yes I like to split hairs. Try fitting a RJ12 plug into an RJ11 socket and you will find out why.

  31. Robert Says:

    I made this circuit and it appeared to work fine at first.
    However, those on the recieving end complain about echo.
    I think this is caused by the circuit, because noone complains when
    I use the computer’s microphone with headphones.

    I would like to understand how this ciruit splits/joins the mic and ear
    signals so they fit on the same wire, then I might be able to figure out
    why my circuit doesn’t work. It maybe that the voltage isn’t high enough,
    or maybe the capacitors aren’t working properly.

    Where can I find this information? Any ideas?

  32. Robert Says:

    Some further experimenting shows that with the adapter plugged in,
    when winamp plays, audiograbbers VU meter is going up and down. This is
    without battery or phone attached. Clearly, there is crosstalk between my
    speaker and mic connections. Should this be so?

  33. Goran Says:

    Hi, I am curious what happened with ringing circuit tweak for this adapter. Has anyone found some working solution?

  34. Fraide Says:


    Your solution seems rather interesting, but, my PC is a Mac !
    I noticed on the Skype accessory page that the wireless adapters and headsets, although they are expensive, are not supporting Mac os system (for some unknown reasons, skype never answered my question about it).
    Do you think your solution would work nice on a Mac ?

  35. Hasan Bazerbashi Says:

    This was very usefull and easy! thank you very much Chris J for sharing and thanks for grynx for hosting :)

    You guys make the world a wonderful and interesting place 😛

  36. P.O. Says:

    In the newest version of SKYPE (2.0) you can click in a checkbox so the built in speaker of the computer rings. If you use a longer cord from the computer to an external speaker, you will be able to hear the rinsignal. Perhaps this is an idea for someone to build something to use together with our housephone.

  37. James Says:

    I live in the US. Can somone get me the part numbers for everything that i need. I was going to try and just shop for everything on Radioshack. Thank you guys in advance this is a great idea.

  38. Saeed Says:

    can i use two resistor of 250 Ohm instead of 500 ohm veriable resistor?

  39. Saeed Says:

    i m looking for help on polarity of capacitors,keeping in veiw this diagram + or – of capacitor will\
    be connected mic and + or – spaker one cable

  40. Vincent Says:

    I have testified the ciruit and in reply to Demon (Q4) and Saeed (Q38 & Q39), the 500 Ohm resistor can be removed as the mic
    and speaker out use the same ground on the sound card. For the polarity, put spk–>( + – ) and (+ – )–>mic back into the circuit
    or they maybe reversed with the the reversion of the battery polarity. Battery with smaller voltage, say 4.5V and
    capacitors with lower capacitance like 2.2uF(225) may also work. The volume level is better than that with isolation transformer.
    Please leave your e-mail address for a modified circuit.

  41. saeed Says:

    Thanks Vincent for guiding it working now but as other people say in microphone test voice is some what low. Any body got solution for this problem? i also got help from this web link

  42. Jay Says:

    James, I just built mine from RadioShack. Used the 4.7uF as they did not have 3.3 and 100 Ohm. Left outh the 500 Ohm Riostat and used the 9v battery. I have a little bit of static but that is my cordless mouse. Other than that it works great.

  43. gamati Says:


    there is something interesting for skype, you just do NOT have to have your PC turned on all the time.

    i found that at:

  44. m Says:

    hi all –
    i built this circuit and encountered a very annoying problem. on my part it works perfectly but everyone who wishes to talk to me hears what she sais again (with a latancy of about 0.5 – 1 sec, matches pretty well the roundtrip time of the data). its some sort of crosstalk/feedback (from SPKR OUT to MIC IN). i’m pretty sure the circuit is built correct – any suggestions on how to resolve this matter?
    thx m.

  45. Greg Says:

    Hi M. Thanks for confirming the circuit error (in post #286 at: ). I was waiting for that, after commenting on it myself.
    Regarding the echo problem you described, if the person you talk to hears a delayed echo, it usually means your audio output is too strong. Usual remedy is to switch off mike boost and turn audio volume down. If doesn’t fix, then reduce audio output level using a voltage divider, or (easier): plug chatcord into LINE IN on soundcard instead of microphone input.
    Regarding resistor-based “chat-cord” circuit versus the transformer solution, transformer probably offers better protection for the soundcard, but the resistor method seems to work just as well in terms of performance.
    Regards, Greg

  46. Greg Says:

    Sorry I mixed up two people: Thanks Amateur for your info about this resistor-based circuit, which is very useful.
    See post #286 at
    Regards, Greg

  47. Nit Says:

    I’m wondering if using a 9V battery, how long will the battery last?

  48. Adam Says:

    Could somebody please make the revised version into a schematicas I am confused by the explanation

  49. Vitali Virulaine Says:

    Listen people. I’m the publisher of Simple skype voip analog adapter.
    I saw how to improve this device, but I have no time for experiments. Please if anyone can improve this – send me the schematics at and I will publish it on this projects main site
    Thank you.

  50. enbee Says:

    I built this unit yesterday and after a bit of frustration (before finding my old power supply unit was dead)got the unit working just fine. Thanks for the easy to follow instructions.
    I have a lot of feed back coming through both the ear piece that I can hear and the mic that the other end can hear. I assume it comes from the power supply but I’m not sure.
    Any ideas on howe to reduce the noise?
    Thanks in advance.

  51. gahbahj Says:

    i built this interface and insatalled the chatcord dialer software which attempted to run a setup wizard for audio etc. but froze and eventually gave an out of memory error. starting the app again tells me its expired. is there another source for [chatcord] dialer software?

    enbee – how were you able to setup and test yours? thanks for help

  52. Marcelo Says:

    Hi Guys… I was having echo problems as well. I tried using MSN instead of Skype and it’s gone! I think because
    MSN cut’s off the conversation (doesn’t send MIC and SPKR same time).

    Ok, but still trying with Skype or
    google talk… i figure out that the echo problem is caused by your voice coming in MIC IN (but in the other
    side of conversation), so you have to tell your friend abroad to turn the PLAYBACK MIC sound recording on MUTE,
    and leave turned on, just the MIC on RECORDING MENU, NOT THE PLAYBACK. (You can make this on your computer as well)

    This should solve.

    One Doubt: What the 500 POT resistor do ???? Is it for telephone gain ?
    Thanks man, help with any ideas!

  53. DD32 Says:

    The main echo issue is that the remote person will hear their own voice back, usually at a louder volume than local persons voice.
    This is caused by the audio coming from the computer, going through the phone and coming back out to be picked up by the micrphone input.

    So far, i’ve not found a way around this..

    This one is better for it:
    I cant fiund any Center tapped transformers locally though, So i’m going to try a different one from here: (Search for “Operational amplifier based hybrid circuits”)
    it uses an Op Amp to remove the remote persons voice.. I’m yet to pick up an IC yet tho for it..

    I’d like to know if anyone else has any other kind of ideas.

    Also, the 500ohm pot was mainly to reduce teh volume i thought, I didnt even bother putting it in the circuit at first, and it didnt help the echo issues by putting on in either..


  54. DD32 Says:

    Also an IMPROVED VERSION was put out recently:

    direct link:

    Not that it seems to change much.


  55. Greg Says:

    Chat-Cord DialerSK software stopped working a month or so ago and just gives a message to the effect that it has expired. The software has been withdrawn from the Chat-cord site too. I don’t think these two observations are coincidental. I tried other versions of the software, but they all give the expired message.
    I’m just guessing, but you probably have to buy a Chat-Cord in order to get a working (non-demo)version of the DialerSk software. Oh well, it was fun for six months. Thanks Chat-cord people (he he!!).
    Regards, Greg

  56. Greg Says:

    The improved circuit
    corrects an error in the original circuit. The 500 ohm pot is to adjust the impedance to 600 ohms, as seen by the phone line. In the original (incorrect) circuit, the pot was shorted out, so it did nothing.
    If the person you are talking to hears a delayed echo, turn off the microphone boost and turn down the mike gain. Alternatively, use LINE IN on the sound card, instead of MIC (adjust soundcard control panel accordingly so the recording source is LINE IN, not MIC).
    Also, avoid listening to the audio through the PC speakers instead of the phone earpiece, otherwise your mike will pick it up and feed it back, giving delayed echo.
    Cheers, Greg

  57. Greg Says:

    Nit (post#47), re: How long will 9 volt battery last? Current draw at 9 volts is about 20-25 mA (depends on phone), so small size 9v battery will not last long in continuous operation, maybe a week, or longer if alkaline (expensive!).
    Better to use lower voltage and larger capacity batteries, eg AA alkaline. I use two (=3 volts) with a cordless phone which draws 5 mA only at this voltage and still works fine; so batteries will last hundreds of hours (and have done so).
    Some phones need 4.5 or 6 volts to work. Current drain increases with voltage, so use lowest voltage that will still power phone properly. Could never get USB power to work properly: too noisy. Cheap motherboard?
    Regards, Greg

  58. Toyo Says:

    I have just assembled my adaptor using the 9V batery, 2 – 100 ohm resistors, 2 – 2.2 uF (25V) capacitors and 1 – 300 ohm resistor (parts that I had available). Built using the improved circuit ( Everything fit in an old DSL filter case and it is working great! Thanks !

  59. Marcelo Says:

    reply #53
    Thanks DD32,

    have you tried
    this ?
    i´m still having echo problems… still thinking like a trick to close MIC when SPKR is on…
    any suggestions ?

  60. DD32 Says:

    I didnt get around to trying it. I Ended up giving up trying to get that method working, and went back to connecting the wires directly to the phone pcb.
    Not that i anylonger have a use for it..

  61. Marcelo Says:

    I was trying to put a inverting ampop in the speaker, processing and subtracting the signal from mic… but it wasn’t perfect….
    If anyone want to try…

  62. CDG-Video Says:

    The echo problem problem that is heard by the far-end is caused by the portion of his audio that is across the 100 ohm Mic input resistor. This is sent out via the Mic Input and the far-end hears this as echo with about a 1 sec delay. I solved the echo problem by connecting the audio card ground to the junction of the two resistors (100 ohms, I used 150 ohms).
    Connect the other end of one resistor to the audio card’s Spk Out via a 1.ouF non-polar capacitor and connect other end of the other resistor to the Mic-In via a 0.001uF cap in series with a 200K ohm resistor which will reduce the mic’s audio level. (You may have to experiment with value from 100k to 620K.)

    If you remove Chat-Cord@DialerSK, change date to before 1 Jul 2006, and then re-install, the ChatCord dialer will work.
    …have fun !!!

  63. Vitali Virulaine Says:

    Hi people! I had published new version of it’s adapter! WITHOUT ECHO problem (as i think). I hadn’t tried it yet. But people say that ir is working!

  64. Vitali Virulaine Says:


  65. Marcelo Says:

    I solved the echo problem as well…. i just put a ampop subtracting, with the
    references between the signal from SPKR OUT and the OUT Signal (from the circuit). The ampop
    will just subtract the signal from SPKR of the mixed signal (OUT from the circuit)…. So a
    clean signal will be free to MIC… no more re-gain….
    If you wanna try i can send details….

    I didn´t tried this other version of the circuit, does anyone know if works ??
    see you guys,

  66. CDG-Video Says:

    Hi Marcelo,
    Congrats on another method for fixing the echo problem.
    I would suggest that you send your schematic and info re the op-amp solution to Vitali at and he will post it on his web site and thus share the info with all. Thats what I did with my mod for fixing the echo.

  67. Marcelo Says:

    Ok! i will send a schematic of ampop solution. i didn´t try (CDG-Video) solution,…it seems to be
    easier and cheaper, ….

    I´m busy at this weekend, as soon as possible i´ll send the email…

    another doubt,.. using the skype, do you guys know how to disable default mic molume control ?
    i have already disable the skype control, but it still increasing mic volume….
    see you…

  68. Tim Says:

    I tried the CDG-Video solution and I still get echo.The only thing I didn’t have the exact values for were the R1 and R2, which are 100 Ohm instead of 150 Ohm. I’m not sure how much of a difference that should make, but that’s my experience.

  69. CDG-Video Says:

    My experience has been that there is a slight echo only when both parties talk at the same time.
    If yout have a lot of far-end echo, you should double check your wiring of the adapter. The audio card’s ground must be connected to the junction of the two resistors (ie connect resistor juncion to the sleeve (or screen) connection of the mini-plugs for Spk-Out and Mic-In). If your wiring is correct, then try lowering your recording microphone volume when the far end complains about echo. This should reduce the echo. (Also mute the playback mic volume)

    I have since increased R1 and R2 to 300 ohms, thus putting a total of 600 ohm across the tip-ring of the cordless phone, to better match the telephones AC impedance and this has further reduced the far-end echo. Now R1=R2 = 300 ohms, and the tolerance of R1 and R2 is 1%. (I used four 150 ohm 1/4 watt; 1% tolerance resistors. I got a package of 20 for $2.99 at Active Components store here in Canada). Hope this helps.

  70. CDG-Video Says:

    I also forgot to mention that within the Skype software, under Tools ->Options ->Sound Devices make sure to select “Let Skype adjust my sound device settings”. This will keep your mic volume from getting too high, which otherwise would cause echos. Give it a try and let us know if you get any improvements.

  71. Tim Says:

    CDG-Video. Thanks for the feedback–I was actually hoping that I had done something wrong. I’ll check the wiring and other things you suggested. I’m guessing that my ground/signal are mixed since I didn’t pay any attention to that when wiring it together.
    Thanks again for the help. I’ll post back here with my results once I get the time to try your suggestsions.

  72. Marcelo Says:

    Yes, Tim, letting us now about a feedback, is important….
    Anyone know a good/cheap ampop to audio signal ? (i used tl071)
    i’ve a got a little, little, distortion, but it’s ok…

  73. Tim Says:

    I checked the wiring and it was indeed flipped around. I don’t have the echo problem anymore–it’s amazing what happens when you construct the circuit correctly :). Thank you for the help.

    And does anyone know a good replacement for the chat-cord dialer software that can dial numbers in skype using the phone keypad? I tried using that, but it says that the program is expired. I found a similar program called Phone Converter, but it hijacks the skype window so that I can’t open it up–very annoying.

  74. CDG-Video Says:

    I have revised the adapter to version 1.2. This overcomes two problems…speed-call dialing now works reliably and the mic level has been adjusted to near-max so that the “AGC action” of the mic level by the software, is now resticted and this reduces far-end echo. For version 1.2; both caps C1 and C2 were eliminated and a new additional resistor R4(1K)is connected from the Mic-In to ground. The attenuator formed by R3 and R4 is used to set the Mic level to near-max value. For my audio card (Ensoniq ES1370), R3=100K. You may have to adjust R3 to set the “near-max” level for your particular audio device. The telephone termination(R1+R2) is now 600 ohms to better match the telephone’s impedance. I used four 150ohm; 1/4W; 1% tolerance resistors for this termination. The other resistors can be 1/4W, 10% tolerance.
    I have sent Version 1.2 schematic to Vitali.

  75. Marcelo Says:

    Nice one man!
    works great!

  76. Bob3 Says:

    Where does version 1.2 its power? I can’t get it to work.

  77. lalit jain Says:

    sir i am getting a lot of echo from the calling person.please provide me with the complete circuit diagram.

  78. KraftWerk Says:

    Im the atenna catching vibrations, youre the transmitter…give information!

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