Additional device for the telephone not-hang-up reminder circuit

If the user does not hang up the phone properly after answering the call, and the other party happens not to hang up the phone properly either, it will often cause additional economic losses to the user. Therefore, the author introduces a novel telephone attachment device, which can issue an alarm when the handle is not pressed properly or the hands-free key is not reset after the call is finished, so that the call is still in the state of not hanging up.

Working principle: The circuit is shown in the attached figure. When the phone is picked up and connected to the phone load, during the positive half cycle of the external line pulse current, the current passes through LED1, R, VD3 and the phone to form a loop, and LED1 is forward-conducted and lit. During the negative half cycle, the phone, VD2, R, and LED4 form a loop, and the current flows through LED4 to light up, prompting the phone to work. After hanging up, the current loop is cut off, the LED goes out, and the phone does not work. R is the current resistor, and the resistance value depends on the performance of the LED. The circuit can be installed in the power supply external line box, and two small holes are drilled on the box surface to expose LED1 and LED4. If you want sound and light prompts, you can connect the beeping music sheet to both ends of the LED.