Ok, this project is not any research for serious Wireless Power, with high efficiency, it is just some free time Microcontroller project, and all the variable and setting in this project is being obtain through try and error, and it doesn’t involve any complex calculation for electromagnetic stuff. Do comment if you have any idea or better way to improve the system.
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Basically, I have a Sun Jar, which is a solar powered lamp, that it is like you could store the sunlight in the jar. Charge it up at daytime, and use the light at night. (you can Google “Sun Jar” for more information)
Solar panel inside, with a switch to choose Blue or Orange light, and a Light sensor, to automatically turn it on when it is dark. 1x AA battery to store the “sunlight”.
My problem is I don’t have direct sunlight into my room at daytime, that I could use it to charge up the Sun Jar. To charge it, I’ll have to bring this Sun Jar out to my corridor to charge it up, and bring it in at the night. So, I decide to power the Jar up using my USB port, but the whole jar is made of Glass, that I cannot drill a hole for my wire to go into the jar, so, I come out with this idea of creating wireless power to power up the jar.
The main part of the Wireless Power system is the wire coil. I am using small (I don’t know the exact size) multicore wire, and i made it at the size of around 10cm diameter, 15 turn (number of turn, I simply choose 15, no special reason, do leave comment if you have any idea how the number of turn affect the wireless power system). You will need two exactly same coil (one for the LED at the Jar, one to be connected to UMK8), its like one transmitter and one receiver.
The overall system is something like a transformer, where there are primary coil and secondary coil. The UMK8 will generate a pulse at certain frequency to the primary coil, and at the secondary coil, we will have the LED collecting the “wireless” power from the coil. We all know normal transformer works only for AC system, and that's the reason we need UMK8 to generate pulse at the primary coil side.
At the UMK side, I add in external 20MHz Crystal to enable UMK to generate higher frequency for the coil. The complete schematic for UMK8.
Besides of the Crystal Oscillator, I also add in a push button, a LED, and for the output, I use 2N2222 transistor to drive it, to ensure that it provide sufficient current to power up the coil. About the push button S1, there is no need to put extra pull-up resistor because PIC12F683 do support internal weal pull-up on its I/O. You’ll just need to configure that in your coding.
One thing to take care while soldering the UMK8 is try to leave some space between the Crystal Oscillator and the PCB, because it is double layer pad, try to prevent the body of the Crystal Oscillator touching the pad, or it is better if you have a plastic spacer in between them.
More information about UMK8 Here:
UMK8 Product page
For the LED in the Jar, I cut off some part of the “head” (refer to the image) of the LED using wire stripper, because normal LED is design to focus all the light to the “head” of the LED. For this application, to light up the Jar, its better if more light could be reflected to the side of the LED. So, it do light up the jar better with the “head” cut off.
Then, connect the coil to the LED, directly, one wire to one pin, and mount that LED together with the Solar LED in the Jar. I keep the whole Solar system of the Jar, that I could still “capture” sunlight if I want, and this wireless power will work independently. So, I could use either “sunlight” or Wireless Power, and they didn’t affect each other.
Secure the Wireless Power LED to the Solar LED using Shrink tube. Try not to put them side by side that they might block each other lighting.
Placing the cover back, and both LED work nicely.
So, the coil will be place inside at the bottom of the Jar, and the wireless power comes from the bottom, while the solar power from the top.
At the UMK8 side, connect the 2nd coil to normal Female Header, and its ready to transmit the power wirelessly. If you want, you can also create a base plate for the Jar. I am using some kind of foaming material, and a cd envelop. Cut out some of the foam for the coil, and use some transparent tape to hold the coil to the foam. Insert it into that envelop.
For the coding for UMK8, you can download the complete project at the end of this article. The coding basically generating a pulse to the coil, and the button is to turn the pulse On or Off. Try to refer to the comment in the coding and do leave comment here if you have any doubt about the code.