Telephone call display equipped with self-powered and self-charging

The author used existing electronic components to make a telephone call display equipped with a self-supplied and self-charging power supply, so you no longer have to worry about changing batteries.

After installing as shown in Figure 1, the assembled circuit board can be installed in the phone. Install the rechargeable battery in the battery compartment, and connect the positive and negative polarity to the power supply of the local telephone line terminal block. It is recommended to set the multimeter to the DC voltage range to confirm the polarity. Solder the "+" and "-" leads of the self-powered self-charging power supply to the "+" and "-" power terminals in the battery compartment, respectively.

The self-powered, self-charging power source draws 50V DC from the telephone line voltage, passing through diode VD1, half-wave rectification, and current limiting resistors R1 and R2. The resulting voltage is approximately 3.8V DC, which is then stabilized by VD2 to approximately 3.1V. In addition to rectification, VD1, due to the diode's characteristics, conducts in the forward direction and blocks in the reverse direction, ensuring that the rechargeable battery does not discharge into the external circuit. After all components are connected, the entire circuit is secured in the spare space of the telephone. As long as the wiring is correct, installation is complete. VD1 uses a 1N4007 silicon rectifier diode; VD2 uses a 4.5V-6V, 0.25W silicon Zener diode, most commonly 2CW52 or 2CW51. R uses a 1/4W carbon film resistor, and C uses a CD11-12V electrolytic capacitor (1000μF).

G is to use AAA rechargeable battery. The area of ​​the circuit board is determined according to the space inside the machine.

If your phone is equipped with the above circuit, the battery will normally maintain voltage, with a low charging current (known as float charging). This will prevent the battery from heating up and provide a service life of 5-6 years. The battery will only power the phone during field maintenance or a power outage, ensuring the preservation of existing data.