The company Apple, recently introduced the wireless charging technology. It is a great news to many of us, but what's the technology behind it? And how does wireless charging works? In this tutorial, we are going to learn how does wireless charging works, and how to actually build one ourselves! So lets not waste anymore time, and start our journey to success! And I'm your 13 yrs old tutor, Darwin!
Step 1: How Does Wireless Charging Works
Now let's see how does wireless charging works. You may know that current flowing through a wire creates a magnetic field, as shown in the first picture. Magnetic field generated by the wire is very weak, so we can wind up the wire to form a coil, and get a bigger magnetic field, as shown in the second picture.
Also in reverse, when there is magnetic field near and perpendicular to a wire, the wire will pick up the magnetic field and current will flow, as shown in the first picture.
Now you might have guessed how does wireless charging works. In wireless charging, we have a transmitter coil which generates magnetic fields. Then we have a receiver coil which picks up the magnetic field and charge the phone.
Step 2: AC and DC
AC and DC also known as Alternating Current and Direct Current, are very basic concept in electronics.
DC, or Direct Current, the current flows from a higher voltage level to a lower voltage level, and the direction of current does not change. It simply means that if we have a 5 volt and a 0 volt (ground), the current will flow from the 5 volt to 0 volt (ground). And the voltage can change as long as the direction of current flow does not change. As shown in the first picture.
AC, or Alternating Current. However as the name suggested that it has an alternating direction of current flow, what does it mean? It means that the current flow reverses after a specific time. And the rate of the current flow reverses is measured in Hertz (Hz). For example, we have a 60Hz ac voltage, we will have 60 cycles of current reverses, which means 120 reverses, since 1 cycle of AC means 2 reverses. As shown in the first picture.
These are very important to wireless charging circuit. We need to use AC to drive the transmitter coil, since the receiver can only generate electric signal when there is a alternating magnetic field.
Step 3: Coils: Inductance
You know how a coil creates magnetic field now, but we are going to dig deeper. Coil, also known as an inductor has a inductance. Every conductor has an inductance, even a wire!
Inductance is measured in "Henry" or 'H'. milliHenry(mH) and microHenry(uH) are the most commonly used unit for inductors. mH is *10e-3H, and uH is *10e-6H. Of course, you can even go smaller to nanoHenry(nH) or even picoHenry(pH), but that is not used in most of the circuits. And we usually don't go higher than milliHenry(mH).
The higher the number of turns for coils, the higher the inductance.
An inductor resists changes of flow of current. For example, we have a voltage difference applied to an inductor. Firstly, the coil doesn't want to let current flow through itself. The voltage keeps pushing current through the inductor, the inductor started let current flow. At the same time, the inductor is charging up magnetic field. At last, the current can completely flow through the inductor and the magnetic field is completely charged up.
Now, if we suddenly remove the voltage supply to the inductor. The inductor doesn't want to stop the flow of current, so it keeps pushing current through it. At the same time, the magnetic field started to collapse. Over time the magnetic field will be used up and no current will flow once again.
If we construct a graph of voltage and current through the inductor we will see the result in the second picture, the voltage is represented as "VL" and current is represented by "I" the current is shifted around 90 degree to the voltage.
At last we have the circuit diagram for an indcutor(or a coil), it is like four half circles, as shown in the third picture. An inductor has no polarity, which means that you can connect it to your circuit in any way.
Step 4: How to Read a Circuit Diagram
Now you've know pretty much about electronics. But before building something useful, we have to know how to read a circuit diagram also known as a schematic.
A schematics describes how components connect to each other, and it is very important as it tells you how the circuit is connected and gives you clearer idea of what's going on.
The first picture is an example of a schematic, but there are so many symbols that you don't understand. Each specified symbol like L1, Q1, R1, R2 etc. is a symbol for a electrical component. And there are so many symbol for components just like as shown in the second picture.
The lines connecting to each component is obviously connecting one component to another, for example, in the third and fourth picture, and we can see a real example of how a circuit is connected based on a schematic.
The R1, R2, Q1, Q2, L2 etc. in the first picture is called the prefix, which is just like a label, to give the component a name. We do this because it's handy when it comes to PCB, printed circuit board, soldering.
The 470, 47k, BC548, 9V etc. in the first picture is the value of each component.
This might not be a clear explanation, if you want more detail, go to this website.
Step 5: Our Wireless Charging Circuit
So here is the schematic for our design of wireless charger. Take some time to look at it and we will start the build! Clearer version here: https://easyeda.com/darwinenergy/Wireless-energy-driver
Explanation: Firstly, the circuit receives 5 volts from X1 connector. Then the voltage is being stepped up to 12 volts for driving the coil. The NE555 in combination with two ir2110 mosfet driver to create an on off signal which will be used to drive the 4 mosfets. The 4 mosfets turns on and off to create an AC signal to drive the transmitter coil.
You can go the the above listed website and scroll to the bottom to find the BOM(bill of material), and search for those component except for X1 and X2 in lcsc.com. (X1 and X2 are connectors)
For X1, it is a micro-usb port, so you need to buy it here.
For X2, it's actually the transmitter coil, so you need to buy it here.
Step 6: Begin the Build!
You've seen the schematic, and let's begin the build.
Firstly, you'll need to buy some breadboard. A breadboard is like on the first picture. Each 5 holes of the breadboard is connected to each other, shown in picture two. In the picture three, we have 4 rails which is connected to each other.
Now follow the schematic and start the build!
The finished results are in picture four.
Step 7: Adjusting the Frequency
Now you've finished the circuit, but you still want to adjust the transmitter coil frequency a bit. You could do that by adjusting the R10 potentialmeter. Simply take a screw and adjust the the potentialmeter.
You can take a receiver coil and connect it to an LED with a resistor. Then place the coil on top of the transmitter coil as shown. Start adjusting the frequency until you see the LED is at its maximum brightness.
After some trial and error, your circuit is tuned! And the circuit is basically complete.
Step 8: Upgrading Your Circuit!
Now, you finished your circuit, but you might think that the circuit is a bit unorganized. So that's why you can upgrade your circuit, and even turn it to a product!
Firstly, it is the circuit itself. Instead of using breadboard, this time I designed and ordered some PCBs. Which stands for Printed Circuit Boards. A PCB is basically a circuit board that has connections on itself, so no more jumper wires. Each component on a PCB also has its own place. You can order the PCB at JLCPCB for very low price.
The PCB that I designed was using SMD compoents, which is Surface Mount Devices. Which means the the component was directly soldered onto the PCB. Another type of component are THT components, which we all just used, also known as Through Hole Technology, Is that the component go through the holes of the PCB or our circuit board. The design is shown in the picture. You can find the designs here.
Secondly, you can 3D print a enclosure for it, the link for the 3D stl files are here.
That's basically it! You've successfully built a wireless charger! But always check if your phone does support wireless charging. Thanks a lot for following this tutorial! If there are any question, feel free to email me at email@example.com. Google is also a big helper! Bye.