**The Project**

I am trying to build a circuit that will allow gadgets that are usually charged by USB to be charged wirelessly. As an example I am reverse engineering an A4tech battery-less mouse. However it is too great a challenge for me and I am seeking help from you. I thought it would be better for me to turn this into a group effort than to ditch the project. I will give a detailed description of what I have built and learnt and hopefully you can tell me where I went wrong.

**Signing Up**

## Step 1: Background Information

The mouse I was talking about (see other picture) in the introduction is exactly the same as the Splashpad it uses induction to transfer power across an air gap. This is the same technology as RFID; in fact it uses this to communicate with the pad. To make our own wireless device we need to know more about induction.

Regarding your question about voltage across the primary, I assume you mean a.c. voltage. The drop across the primary is proportional to the impedance of the primary at the signal frequency. This will depend partly on the reflected impedance from the secondary. And, I couldn't find the refrence to your operating frequency, but check the specs on your meter to see if it measures at that frequency.

One solution If your portable device can be kept in one position during power transfer and it does not need to be movable during transfer like the mouse, then you might want to consider taking a ferrite core and saw it in half (probably need a carbide blade for this). On one half wind your primary, on the other half wind your secodary. Mount the halves of this transformer in their respective devices so that you can re-contact the two halves by placing one device on top of the other.

This way, using a ferrite core, you would have better coupling and you could operate at a lower frequency than with an air core transformer.

Hi , i want to build wireless transfer coil antenna to get 12 v and 5 v , how do i calculate the number of winding of the coil and the diameter and thickness of the coil , whats the right formula to be calculate to get the right coil please.thanks

Alan Yate's site has a very nice outline for this entire project. Highly recommend checking his stuff out. About higher frequency, the higher your frequency the less inductance you'll need.

or

.00018 uF

here's a handy link:

http://www.electronics2000.co.uk/calc/capacitor-code-calculator.php

You say throughout the instructable that you want a high frequency. For an inductive coupling application, however, high frequency is not a good thing. To fix this you could try adding a capacitor in series with the coupled signals, as sort of a filter. You could also try lowering the frequency.

PLEASE!

Would increasing the voltage and number of coils on the primary also provide a marked improvement?

Also, how did you wind such nice coils?

4 pegs and a pegboard

4 pencils and two friends

A very well-trained cat

...basically anything that has the ability to have four rectangularly spaced supports ought to do the trick

Anyone has infomation on how to determine the mutual inductance or coupling factor? And also the equation to determine the inductance of the coils?

hope if anyone can help me :(

rgds

alex

M=N1*N2*Phi=K * (L1*L2)^.5

where N1 is the # of turns on the primary, N2 is the # of turns on the secondary, and Phi is the permeance of air.

From this you can extract K, the coupling factor,

K= (N1*N2*Phi) / (L1*L2)^.5

As for determining the inductance of the coils, if you do not have a multimeter or some other device to measure this, you can sweep the frequency on a frequency generator looking at the voltage across a parallel cap and your coil. The peak voltage is then related to 2*pi*f = 1/(L*C)^.5

also, where is the power regulation for the mouse?

why not sine wave ?