The UK system of telephone wiring is different to many others because it uses three wires to interconnect the phones unlike the American system which only uses two. The third wire is the bell wire. This carries the ringing current between the sockets. At the Master socket there is a capacitor between the "B" wire on terminal 2 and the "Bell" wire on terminal 3.

By disconnecting this wire from the master socket it will stop the bells from ringing on all other phones in the house although the master socket will always ring. The circuit shown below will disconnect the bell wire to all the secondary sockets when the relay is operated.

The most simple method of operation is to operate the relay at night so that the phones don't ring in the middle of the night and wake you up. If you have an answering machine connected to the master socket it will take the calls without you being disturbed.

Taking this idea a step further, by connecting a Caller ID aware modem or similar PC interface device to the master socket, your Home Automation system can take control of the bells on your telephone line. You can now use the Caller ID information to control the ringing.

• This may be as simple as allowing certain number to make contact at any hour of the day or night. If the relay was operated to silence the bells but the Caller ID indicated that the call was from someone you allow to call anytime, the system releases the relay and the phones start to ring.
   
• Call Screening can be accomplished by keeping the relay permanently operated so that the phones never ring. If the Caller ID is someone you wish to speak to then the system releases the relay and the phones ring. Once again the answering machine will pick up any calls you don't want to handle.
   
• *%!# OFF you unwanted telesales person. With some of the higher spec modems it is possible to dispense with the answering machine and have the PC play a suitable message down the phone. Again this can be a tailored response based on the Caller ID to give a courteous message, a personalised message or a DONT EVER CALL ME AGAIN BECAUSE YOU ARE BLACKLISTED! message.

I cannot guarantee that this circuit will work with all telephones as some of them do not conform to the UK three wire wiring. Please dont ask me for software for the PC as this will be different for almost every user and I havent got this in use on my system. There are several software packages available on the net for Caller ID interfacing and if anyone has some good links I will add them to this project.