This Instructable will explain how to build a circuit meant to wirelessly light up a LED using induction, inspired by earlier Instructables.

Step 1: Components

The necessary components are:

Battery: 6 Volt (output smartphone charging device will work as well)
Transistor type BF494 or similar
Capacitor 0.1 μFarad
Inductor 330 μHenry
Resistor 33 kOhm
Copper wires (for coil)
Red LED (smallest requirement of voltage)
Breadboard
Wires
Tools for soldering

Step 2: The Circuit

In short the circuit changes the DC output of the batteries to a high frequency switching (AC) current. This current is led through coil 1, where it creates a constant changing magnetic field. When coil 2 is placed exactly above coil 1, this changing magnetic field induces an electromotive force in coil 2. This force causes the LED to blink. Due to the high frequency power transistor (BF494) in the circuit the frequency of the generated current in coil 2 is so high that the blinking will be perceived by the human eye as if the LED glows continuously.

Step 3: Construction

First, test if all electronical components are working. After verifying this, we build the circuit shown in step 2 on the breadboard. Then we created coil 1 and 2 by wrapping the copper wires around a round object. Coil 1 was soldered to the circuit, coil 2 to the LED (no need to worry about the polarity of the LED, as explained in step 2 the current in coil 2 is an AC). Then we connected the circuit to the battery.

Step 4: Testing

When coil 2 was placed exactly above coil 1, the LED would shine lightly. It is important to keep both coils parallel to each other and make sure they do not touch. The test showed us that the circuit was working.

Step 5: Further

The next step in our project will be the creation of a circuit that could wireless charge a smartphone. In order to be able to do this, the output of coil 2 must be changed to a 5V DC. In order to do this a bridge rectifier (change AC to DC), capacitor (filter output) and a linear regulator or buck converter (change current to 5V) are needed.

The final result will be a bartop on which smartphones can be charged using induction between coils in the bartop and in the beer coasters. The coil in the coaster is connected to a micro-usb output to which a smartphone (or other device) can be connected. Since regular cardboard coasters don't have a very long lifespan, this coaster will be sealed in plastic to make it waterproof.