A practical phone lighting

This telephone lighting is designed based on the principles of telephone, photocoupler and thyristor. The working principle is as follows:

1. D1~D4 form a bridge rectifier circuit, and L1 and L2 are connected in parallel with the telephone.

2. When the machine is on-hook, the line voltage is about 48V. The current is limited by R1, causing the voltage regulator to break down, the optocoupler IC to turn on, the thyristor to be cut off due to the lack of trigger voltage, and the indicator light is off.

3. When a call comes in, the ringing current is rectified into pulsating DC by D1~D4, which makes the optocoupler turn on and off continuously. The thyristor is triggered by the pulse to turn on and off, and the bulb emits a flickering light.

4. After picking up the phone, the high internal resistance feeding voltage immediately drops to ≤l2V, the voltage regulator tube cannot be cut off, the optocoupler IC is cut off, the voltage on its 4th pin rises, the thyristor is triggered to conduct, and the light bulb lights up.

The characteristics of this circuit are as follows:

1. When there is no phone call, the lights are off and almost no electricity is consumed.

2. The light will turn on after the machine is turned on, and can be used as a dial light.

3. Reminder to hang up: After hanging up the phone after making a call, if the light is still on, it means the handset is not properly placed, reminding the user to hang up correctly.

4. Anti-theft function: If you are not calling and the light is on, you can pick up the receiver and listen. If there is a voice, it means someone is stealing your phone line. If there is no sound, it means the outside line is disconnected, and you can notify the telephone company for repair.

5. Incoming call light prompt: The elderly with hearing loss may not be able to hear the ringing sound; people in noisy shops may not be able to hear the ringing sound. When you see the light flashing continuously, you will know that there is an incoming call.

6. If you are worried that the light will waste electricity when answering the phone during the day, you can also turn off the light.

This circuit has a simple structure, low production cost, and easy-to-buy components. You can choose a 1/8W ordinary resistor. The photoelectric coupling IC uses a four-pin optocoupler such as PC817, and the thyristor can use any IA/400V unidirectional thyristor, such as MLRIOO-6, BT33, etc.