This simple add on circuit prevents misuse of Land Phone and also indicates whether the Phone lines are Ok or not .It is an ideal tool to test the Telephone lines. It lights LEDs to confirm the signals coming in the Telephone lines. It can also be used as a simple Telephone lock to block outgoing calls.
Just connect the circuit to the Telephones lines as shown in the diagram. LED indications as follows.
1. Handset lifted – One LED turns on – Phone is OK
2. Dialling – LED blinks
3. When the other phone attends the call, other LED lights.
4. LED blinks without using the phone – Misuse. Somebody is tapping the lines.
5. When switch SW1 is in OFF position ,no outgoing calls made. Phone gives Incoming calls only.
6. If the switch is in Off position, it should be turned to On position before attending the call to hear voice.