A Simple Wireless Charger For Smartphones

This DIY wireless smartphone charger operates on the fundamental principles of resonant-inductive coupling and electromagnetic energy transfer. The circuit uses a DC power source—either a 9V battery with a connector or a USB cable—coupled with a BC547 or TTC5200 transistor acting as a fast electronic switch. By pairing the transistor with a 1k resistor, the circuit forms a basic oscillator that rapidly switches direct current into a high-frequency alternating current. This fluctuating current is fed into a custom-wound transmitting coil made from 5 metres of 0.3 to 0.4mm diameter enamelled copper wire. As the alternating current flows through the transmitting coil, it generates a rapidly changing magnetic field around the wire loops. When a receiving coil, tuned to a similar resonant frequency and connected to an LED, is brought into close proximity within this magnetic field, Faraday's law of induction comes into play. The external magnetic field induces an electromotive force (voltage) across the receiving coil without any physical wire connection between the two sides. This transferred energy drives the LED to illuminate, demonstrating the physical transmission of power through open air. While actual smartphone charging requires specific voltage regulation and rectification stages, this foundational analog circuit demonstrates the core wireless power transfer mechanisms utilized in modern consumer electronics.