“Skype” is a powerful tool for Voice over IP (VOIP) and it’s beneficial for every problem with transmitting audio signals over the internet. However it’s limited: Free talking without any costs is possible only if both partners are online. Not everybody is sitting all day long in front of a computer!
The standard way-out is using the feature “Skype out”, that means buying credits. With this you can reach every (also cell) phone around the world. My aim is:
Making your own gateway from the internet to the telephone network.
One possible solution:
The first thing you need is a “skype server”. In my case a “ssh”-server was already running using “cygwin”, which is a Linux- emulation for windows. After installing skype and creating a user-name this skype user is available all the time.
For phoning out you also need a link to the telephone system. I use a “DECT- Headset” for a cordless phone network. The handling is very easy: Follow the instruction manual of the headset and the DECT- base unit. There is only one difference to a normaly hand- unit of a cordless system:You can’t dial with the headset but this is not important in our case.
After testing the basic function of “skype” and the headset we need the gateway.
Step 1: Open the headset. Cut off the wires to the microphone and to the speaker.
Step 2: Carefully solder one screened cable to the points of the printed circuit board where the microphone was conducted.
Step 3: Another screened cable solder to the points, where the speaker was connected to.
The cables will be linked later on to the “sound in” and “sound out” connectors of the computer. Take care: At least one of the cables have to be insulated also from ground to ground between headset and computer, the most simple way is using a small AF-transformer.
Step 4: Be very,very carefully when soldering 2 wires to the middle contacts of the multi-function switch on the bottom of the headset. It’s a SMD- switch, so you need a fine solder spike.
After all the open headset should look like this one:
We still need a way to get the dial tone of the telephone in case of calling via skype. Usually you have to push a small button on the bottom side of the headset. In our case we have to find a possibility to remote this with a function of “skype” only.
In the settings you find a helpful feature for this: select for calling sound of incoming call also the PC- speaker!
In normal operation mode of the server the PC-speaker rings only if somebody calls from skype. So we have to trigger the ringing to get the dial tone for the telephone. For this we still need an “AF VOX – circuit”:
The input is connected to one end of the PC- Speaker and triggers finally the headset-switch for getting dial-tone. P1 adjusts the sensitivity, P2 the duration-time of the signal. After the end of a telephone-talk it’s important calling the server via skype once again to shut down the telephone dial-tone. Every call to this skype user leads to a switching of the dial tone, so it’s important to set the rights in the userlist only for people you allow to use the skype-relay.
The dialing through “skype” is simple: take a “DTMF-dialer” (hardware is cheap as it’s also used for remoting answering machines or software) and generate the tones in the AF-way of VOIP. In my case the dial-software is installed on the “skype-server” and can be remoted with VNC.
The hardware-switching is shown here:
Thank you for any questions or hints! Frank Bosse