I need your help. IPT (Inductive Power Transfer)

THIS INSTRUCTABLE IS NOT YET COMPLETE. I have been trying to build a wireless charger but have come across a problem. I have documented what I have done and learnt so far. Hopefully from this you can see my errors and help me out. Please read the last page to see what I think the problem is and suggest any ways to get around this. THANKS

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.

Step 1: Background Information

Transferring power wirelessly is reasonably simple. If you think about it, all transformers are wireless. But we want something that's truly wireless. Like the Splashpad (see picture). It is pretty much a transformer with an air core.
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.

Comments

[aaronmurray]

Great post, thanks for all the accompanying info. Is it possible to dim the secondary by way of reducing the voltage through the primary or does that mess up the tuning of teh coils?

[akshaya ladwa]

i need to charge my mobile by wireless system using wifi radiations & signals

[davelanda]

very well...

[MadScientist101]

how many microfarads is 181K ?

[spark light]

180 pF
or
.00018 uF
here's a handy link:
http://www.electronics2000.co.uk/calc/capacitor-code-calculator.php

[awmayhall]

So I tried using your circuits in a circuit simulator. I couldn't get them to work properly.

[ARJOON]

i need to connect one of the circuits to a transformer without a centre tap how can i do it

[Aiden1015]

 I think your problem is you're having 2 different resonating frequencies. the primary may be at one, but the secondary is at another, thus a low, almost 0 voltage. the easiest thing would be to play with inductor lengths. or figure out which capacitors on the mouse, with the inductor, create the resonator, figure out the capacitor value and calculate the needed inductance for your secondary.

[cerincok]

From your video, the circuit seems to be working greatly. But less power are transferred. What voltage did you get at your secondary coil?.

[puffin_juice]

I dont think my meter can measure such low voltages at such high frequencies. I got a reading of 0.015mV while the LED was glowing.

[BinnX]

Can you tell me which transistors you used.... its no. and what is your wire gauge for primary secondary coil.

[cerincok]

Yep...i think you're right. Maybe you should use an oscilloscope to measure the exact voltage value..

[faham]

Your problem is simple: you have an impedance mismatch. This means that your primary coil is not well matche to the signal source, and to make it work you will need to match the signal source impedance to the coil impedance. Also you can consider the coil and the parallel cap as an LC resnance circuit acting as once circuit. You need a transistor driver and voltage multiplier, do not worry too much about the current now but please lift up the voltage as of now so you can get more transfer of power. Also remeber that the USB is limited in power and the manufacturer have made accurate calculations on how much power to transfer vs matching the impedance. What I would do is the following: The antenna coil must be driven by higher voltage higher current signal source first, since the USB cant provide higher current lets focus on higher voltage. Now charge up this high voltage in a cap and drive it to the coil via a MOSFET transistor with low ON rDS resistance and proper gate charge. I bet once you do that you should be able to then measure much higher voltage than what you reported. The secret to solving your problem is impedance matching... Please let me know how it goes and call me if you have a problem. Good luck... By the way I worked with high voltage security circuits and TV and power transfer circuits and I can help you as my time allows me. 

[EvilMika]

I'm currently working on a similar project.  Have you looked into using a FET Driver instead of a 555 timer?  This will lead you to much higher voltages and current, thus a stronger magnetic field. 

Also, how did you wind such nice coils?

[killersquirel11]

4 Nails and a wooden board
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

[acmefixer]

"A very well-trained cat" -- Hahahahahah!  Cats don't have masters, they have staff!!  ;-)

[framistan]

It is possible your circuit is using more milliamps than your charging circuit is delivering...  Ohms law works only when your source of AMPERAGE is UNLIMITED...  In the real world, you are limited by what your SOURCE can deliver.  For example, if you place two tiny 9volt batteries in series, you will have 18 volts... connect this to your automobile in place of your car battery.  Ohms law says it should work... but you know there are not enough AMPERES AVAILABLE to do that job.  The same is true on little circuits that only draw milliamperes.  If the current source is too low, then amperes will not be delivered and THEN you see the voltage sag down low as result.

[acmefixer]

In the Real World, you're telling us what you observe on the outside of the battery.  But inside the battery there is actually an _internal resistance_.  If that were very, very low, then the 9V battery would deliver as much current as a car battery, but it's not low.  So when you attempt to run your car with it, the voltage drops across the internal resistance, and all you get outside the battery is a very low voltage, what's left after the V drop across the internal resistance.
BTW, if you try to run the car with the two 9V batteries, they will get hot because of the power dissipated in the internal resistance.

There are these car starting packs that you can buy that are very small, and put out a very high current because their internal resistance is very low.  Thus they are able to turn over the engine and start the automobile.

[Gjdj3]

I don't know if you still check this instructable, or if you're even an active member of the community, but I think I may have found the problem.

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.

[arhodes18]

 Can anybody explain the part of the schematic he added in step 10 I can't for the life of me understand it!!
PLEASE!

[hms1018]

Check out this person's instructable!     http://www.instructables.com/id/Wireless-Power-Transmission-Over-Short-Distances-U/     It's pretty cool!

[DarStarr]

Dont power it off the pc. Grab a more powerful adapter that plugs straight into the wall.

[Masteroffencing]

i agree with darstar u should just get a wall mount for it

[gamerjunky09]

Yeah I also agree. I might try to start my own project for my black berry. I will post my figures as soon as i start.

[acmefixer]

A few observations. The smaller coil looks like it doesn't have enough turns. More turns should help. When I say more, I mean double or even more. The full wave bridge is a power waster. I would remove two of the diodes and double the number of turns in the smaller coil, turning it into a center tapped coil. This and the two diodes make a full wave rectifier. The diodes should be low loss, use 1N5817 schottky diodes for these.

[killersquirel11]

Also, with what little I know of electronics...
Would increasing the voltage and number of coils on the primary also provide a marked improvement?

[breadpig]

Hi

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

[EvilMika]

Breadpig, this is simple an air-core transformer so M should follow as such:
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

[paulm]

 Make sure you are perfectly aligned with the primary coil, at an angle of 90 degrees, you will get no power.

also, where is the power regulation for the mouse?

[freeh18]

 why are you using square wave?
why not sine wave ?

[Xellers]

http://www.youtube.com/watch?v=SSgo_N-5JOg

[robotkid249]

PLEASE READ:

What is you simply had an wall wart that supplied 9VAC after it conevrted the '120 VAC. Then run a transistor so the 555 timer, turns the Wall Wart on and off at 120 kHz, providing you with the 120 kHz square wave, AC signal at 9VAC

[edfel01]

wow u put alot of work into this good job even if its not done yet

[headcipher]

Have you tried using a much lower frequency? I know it may not be exactly the same thing, but I am a utility locator, and I use inductive antennas daily to apply a alternating current to a pipe or wire. I do not pretend to understand the physics, but I can tell you the results I see. When using induction I have various transmitters that project signals at these frequencies: 9.82khz, 33khz, 65.5khz, 83khz, and 200khz. My most advanced couple of recievers also measure the milliamps applied to the target for identification purposes I. E. the signal with the highest rating is the target. The lower the frequency the higher the amp reading, but on the otherside of the coin the lower frequency has less penetration. If you ever have an opportunity to use one of these pieces of equipment, turn it on on a plate of any kind of metal and the lower the frequency you use the more likely you will hear the metal vibrate.

[TheMaskedAvenger]

I recently read about an MIT experiment that took this kind of thing to the "next level." It involved using something called "evanescent waves." Here's the article: http://technology.newscientist.com/article/dn12014-wireless-power-could-have-cellphone-users-beaming.html
Does anyone here know more about this? It seems to me that a magnetic field, unless it was really, really strong, would not be able to do this kind of thing.

[tanmanknex]

well, TECHNICALLY it's not really a magnetic field. it's really an electromagnetic field, AKA radio/gamma/microwaves/light.

[Meigus]

I think the problem here is that you simply don't have enough magnetic field strength. The whole point of this newer style transmission of energy is specifically that it's not transferred through light-based resonance. Even if you multiplied the antenna alot, it'd be like someone with a radio near an x-watt transmitter - the inductance of the wire is too small to pick up enough signal to blow. A design advice: try copying speakers. The whole point of speakers is to drive sound, however, speakers work by a permanent magnet being pushed back and forth, in your case it would create a pulsed magnetic field with no modification, other than the possible removal of the springy styrofoam cone (unfortunately, that foam also holds it in place, so you should probably leave it in as it doesn't impede magnetism). This would be a perfect starting point as a second speaker (say, part of a two speaker set) at most, like, 1 inch distance away and proper orientation (facing head on or completely away - any other would incur loss) would feel a significant change in magnetic field, and induce current in it's own winding. A more extreme scientific use: Using the all-purpose magnetic field "resonance" that occurs for any ferromagnetic material, there've been experiments where a magnet was put in someones fingertip. With short training, they could detect positive fields, negative fields, and even low-hertz fields by the magnet pushing/pushing/vibrating. I think the whole point of what I'm trying to explain is this: Instead of a pure electromagnetic wave, which I think you're trying, I believe you MUST transform a constant field into a waved constant field, whether it be normal-magnet based or a DC electromagnetic. This would make a resonant magnetic wave, but not nearly as high frequency as what we'd consider light. A too high frequency actually would be counter productive, there should be a push or pull, too fast and the reciever doesn't have enough time-strength to act, this exact same principle applies to a specific efficiency of a DC motor (I remember the term now, it's called "slip" look it up on wikipedia). An electromagnetic field would only be useful for the transmitter (to strengthen the range and locking strength). I'm pretty sure the constant field is necessary, so for a test, try using a speaker laying face down on your inductor plate (the one you want your mouse on). A speaker should have significantly more windings than your mouse or pad, so a volt-meter should read a high voltage being induced in the speaker. Just try to keep the frequency under 20,000 for the speaker to resonate properly (it should even make an audible tone if the wires from the speaker are shorted). Try a speaker-test after you make adjustments to the pad to improve the efficiency of the transmitter, should make it faster, easier, and more consistent than modifying the mouse. And if you claim "well a low frequency would have to low resistance" then you either need more windings, or a better inductor, or some such thing to increase inductance. The resistance should be basically infinite when the opposing inductor isn't allowed to short/do work. The inabilty to have an infinite resistance is why wall transformers are ALWAYS drawing power, even when the opposite windings aren't connected to anything. And again, if your inductor is in the field but "switched off", 0 ohm transmitter resistance change is failure to transmit power, infinite resistance is perfect transmission.

[tanmanknex]

um... you have pushing twice in the third paragraph on the last line. did you mean to do that?

[thermoelectric]

After looking at the picture of the primary inductor (the close up shot) it seems to have only a couple of turns, Is that true or are my eyes decieveing me? If it's only a couple of turns, it is probably set up sort of like a tesla coil in some ways. That might help you... Just have a look at tesla coils and see if there are many similarities, I think there are..

[viking_r]

HI, I am working on the same project.(for my final year). right now i am working on the primary coil and acc. to my calc. i need to transfer .24 henry though it. for that purpose i need a 32awg wire(copper). my question is do i have to use copper windg. or can i use aluminium wndg also??? i think puffin_juice is usin al wire in video. for rest of the circuit i am currently using function generator.... one more thing is it possible for you guys to post the full circuit diag.(or the one used in the video by puffin_juce) thanx

[puffin_juice]

It doesn't make a difference, any conductor that is carrying current will produce a magnetic field.

[evildoctorbluetooth]

The aluminium wire, (or the lower resistence wire) will draw a higher current, this will mean that a larger magnetic field is induced. if you cooled the primary circuit, you would notice an improvement (although alot of energy would be wasted on the refrigeration.

[frikkie]

the only difference with copper and aluminium wire will be resistance with heat i believe

[Oorspronklikheid]

not really when magnetizing  any element and demagnetizing it again you get a energy loss called hysteresis loss. basically it takes energy to magnetize an element and energy again to demagnetize it again. copper has a very low hysteresis loss compared to other metals, in other words it doesn't stay strongly magnetized.

[viking_r]

is it possible for u to send primary circuit diagram?? if yes pls send it to [e-mail] Thanx

[tanmanknex]

so, the AC circuit DOES work, but not for your purposes?

[-Aj-]

usb ports supply 5v at a max of 500ma

can you not simply use all the stuff from the mouse to power it?

OH also i just remembered, you can buy cheap electric toothbrushes that use inductive charging. they have 2 AA batteries in them that charge through it.

one thing you may be able to do is what i am currently doing, use a dc/dc converter to up the voltage going into your primary circuit.

this instructable
http://www.instructables.com/id/A_high_power_LED_torch_using_a_single_AA_battery/
is the one i am using, also just look around

[ptdamore]

I've looked through most of the comments here, and I see that you've decided to go the forced switching route for your drive circuitry. I was wondering if you ever tried to build the resonant converter in the Univ. of Auckland PDF. I originally went down the same basic road you are on with trying to get everything precisely tuned to the frequency of my 555. After coming across this instructable, I spent a lot of time reading on the interwebs about resonant converters, and I've tried several of the topologies I found out there in a simulator before settling on one to actually build. A lot of the circuits assume you are going to have a split-rail power supply. The converter in that paper works great with a single rail. I built a stripped-down version of that circuit last week (lots of "spare" parts removed) and it's impressive! I took my secondary winding and hooked it right to a 50 Ohm 10W resistor and wound up with about 20.6Vrms. That's about 8.5W. Don't touch that puppy! You won't just be lighting LEDs you'll be making them explode in no time. I've already done this, as I didn't originally think it was going to work very well :). The nice thing here is that the circuit will oscillate at the frequency that is best for the load. I'm not saying that the whole thing couldn't benefit from some math to get the impedances better matched (the sort of math I've sadly long since forgotten), but since the frequency self-adjusts, you are not worrying about the massive switching losses that can mount if your drive frequency is not exactly right, and that seems to be a huge part of the battle. Your switching components will thank you, too. The schematics in that paper are sort of daunting, and with all due respect to the creator, not without some flaws. Some components could be better specified, and his gate wiring is not right. Reading through the rest of the doc, though, you can figure out what he was going for. If you know your load kinda well, don't need the data transfer part, and can find your power somewhere else, you can eliminate a lot of parts and it becomes a lot more simple. I'm currently working on getting my component count down, and making the tiny45 I'm using to control the power-up to do as much work as possible. If anyone's interested, I can post what I did once I get it to the point where I'm happy with it.

[puffin_juice]

Hey Thanks for your post, I have kind of lost motivation in this project and due to all the comments considered taking it down. I just cant answer every comment without actuallyy working on the project. I dont think I'll get back into it anytime soon, maybe once I have learnt how to program microcontrollers because I have realised that the circuit needs some intelligence. I'm telling you this because I think you should definately write an instructable for your circuit, many people could benefit from it. Probably even me.

[8bit]

Well, I better hurry up and save it to my HDD if you're threatening to take it down! I plan on using this - just don't know when.

[robotkid249]

Why don't you use a volt meter to find where (on the receiver circuit in the mouse) the mouse is being powered. Then simply solder two wires on that point and attach it to and LED, PDA, cell phone?

[myfcr]

low tech: magnets spinning as in a homemade ac generator, a single coil in the device (or device charger) with ac to dc circuit + zenner

[8bit]

Is this still a running project? How is it coming?

[cerincok]

hi...puffin, i just want to say that i just did it...I got 2.5 V at the secondary circuit... I'm using Power Pulse Controller circuit...
http://www.rmcybernetics.com/projects/DIY_Devices/homemade_pulse_controller.htm
I'm really exited now and for your info, my supply is just only 9V battery....
To increase the voltage output at the secondary, i just increase my supply voltage..
Once again, i don't this this circuit is using the resonance effect..

Thanks...Hope This can help you..
TQ

[puffin_juice]

Have you got a circuit diagram, I'd be interested in seeing how it works.

[apple perez]

nothing can u give me

[cerincok]

no...it was the close loop voltage...this time i was able to ON the wireless A4 tech mouse with my design circuit.... I'm really impressed myself..because my supply just only a 9V battery. Once again my measured voltage was 4.5V at the secondary. I think this circuit is really working perfectly..I'll post it to you later with pictures and circuit diagram because I've to attend the class right now..

[technopenguin]

Umm.. Don't you need to power the transistor's base to allow current through?

[apple perez]

yes

[technopenguin]

Oh I forgot to look at the top schematic again. Sorry

[Ferenczyg]

I think that basically your antenna input impedance is not matched to the output impedance of your circuit, both in the emitter or the receiver side, or both. normally this is resolved via a adapting network done with resistor and condensers in the emitter or the receiver side, or both. Try to go to microchip side (www.microchip.com) and download the application note AN710. Is for RFID but as 13.56 MHz RFID transmission is done via inductive coupling rather than classic electromagnetic coupling this may be helpful.

[cobra6romeo]

Your project is very cool. I am currently working on something similar. Here is what I have learned about inductors and switching circuits. I hope it helps.

[dciocoiu]

looks like you are trying to make an radio circuit. are you?

[Th3H4rRy]

Hes making a wireless charger for USB devices. Adapted from a batteryless wireless mouse, I thought it looks similar to a radio, Its not

[dciocoiu]

well it shore looks like an radio circuit to me to be more precice an squere wave trasmiter.

[chriskarr]

Yes, this is a radio circuit. That's why it looks like one. The idea is to transfer, without wires, electricity, and it will be in square waves, due to the capacitor. This radio transmitter isn't for transmission of intelligence, however, but, instead, a transmission, via radio waves, to the receiver coil which will pick up the electrical energy (at as little loss as possible) and use it to power small devices.

[frikkie]

If you can build a strong rf transmitter it might work.If you can make an bulb glow from a certain distance then you should be able to charge battery of an usb charged devices.They use very little current so they should charge quick.

[dciocoiu]

how is this circuit going to produce electronic energy?

[yewie56]

Hello Puffin_juice, the Solution is just so simple: First: How many energy would you like to transfer? Charging with 500mA is really fast. Charging a mobile or an USB-Device ist mostly done by 5V. Therefore you need 2.5Watt. Think about efficiency of 50% (If you use metallic cores). Makes 5W transmission energy. Buy a small audio-amplifier module or kit 5-10Watt. These amplifiers can amplify clean sinus-signals. As generator you can use a simple sinus generator schematic. Check, if it can amplify your high frequency. Maybe you need more power because of the falling frequency response curve (If you use a D-Class amplifier module there should be enough headroom). Connect the transmission inductivity via a (safety) series resistor of 4 ohm instead of the laudspeaker. That must be all for your transmitter. Thats the old fashion from Germany to transfer audio signals to disabled persons without the need of a rf-transmitter. They only need a headphone and a receiving inductance. The transmitter inductivity has been mounted around the walls of a room. Let me know, if its functioning. Yewie56 from Germany

[puffin_juice]

Hi Yewie56 Your Idea of using a audio amplifier is fantastic. Now that I have finished my semester I once again have time to concentrate on this, I'm also somewhat smarter :). I'm going to give this a go. I'll let you know of any results. Cheers for the idea, If I use your idea in a instructable I'll make sure it has your name on it. Regards

[guyfrom7up]

that won't exactly work... at least what I'm doing the higher the frequency the more efficient and farther away the device can be. I was thinking of using 1 or 2 megahertz. You then have to calculate the "resistance" of the coil at that frequency, and then you need enough voltage to drive enough amps through. Plus your amp needs to be able to handle the frequency. I'm also working on this... I'm stuck at the sine generator part, lol

[Manriquea]

you need to add a capacitance to your coil specifically for your driving freq, then you will have only omic resistance of the coil to worry about. Read tesla, hes all over this stuff.

[puffin_juice]

Try a triangular wave, that will give you a similar power output. Its also easy to generate because opamps and 555 timers can do it. But if your determined to use sine waves you could consider such oscillators as the colpitts or hartley oscillator. After all those oscillators are used for RF purposes and hence can probably handle high currents unlike digital electronics.

[guyfrom7up]

I was going to go with a pierce oscillator, but I might try a triangle wave, it's much more practical

[Prometheus]

As I read your project, you state that you are having trouble getting power to trnasfer efficiently from primary to secondary. You uses a 555 astable vibrator circuit (which only does on/off operations), and a 556 astable vibrator (same as the triple-5, but regulates duration as well)....

NE555 timer tech page: http://www.uoguelph.ca/~antoon/gadgets/555/555.html

The problem seems evident to me as the following:
The vibrator circuit cannot reach the frequency that might become helpful with this project. This is how TV flybacks work. At 25kHz, you can use only about 3-5 turns of 18AWG wire around a 10mm core and induce 12VDC on that coil, where as static DC would be a direct short. The balance is that higher frequencies degrade to a larger degree in an air-core transformer, so you need to make your switching speed higher, but also increase the efficiency of your transformer.

If you need a few ideas, take apart the head motor of a VCR, noting the contactless coupling between the heads and the drum itself. Magnetic fields decrease by a factor of 4 per distance. For example, if the field is (x) gauss at 1mm, it will be 1/4 of (x) gauss at twice the distance, and continuing exponentially by a factor of exponential decay.

I dunno if this helps, but I hope it at least inspires some thoughts/ideas with you....good luck.

[puffin_juice]

Could you further explain what you said in the second paragraph, I didn't quite follow?

[Prometheus]

Higher frequencies inherently increase the mean resistance of a given conductor. It's hard to explain, but higher frequencies allow you to force a higher voltage through a transformer primary (assuming it responds to that frequency) to get the same results from a smaller unit than typically required by normal Ohm's Law and Faraday's principles. At the right frequency, only a few turns on the primary can be used to push higher voltages through a transformer to increase the output voltage without increasing the size. Television flyback transformers often use only a few turns for the primary, with a result on the secondary at a higher yield than with a 60Hz unit of the same rating. The trick is that they use a higher frequency to "cheat" the laws of impedance, but flyback transformers only respond to frequencies between a certain range, like 20-25 kHz. This allows one to use a turns ratio previously forbidden by low-frequency power, such as 10 turns on the primary at 19V to produce the required 30kV on the secondary, to charge the CRT and allow the h0orizontal divergence to work properly. If this were done with a 60-Hz method, it would take a transformer far larger, like needing a neon-sign transformer for every CRT, which is easily 100x the size of a standard flyback transformer used today, due to the frequency-response required of the transformer core.

[Zorink]

Isn't the turn ratio voltage increase kind of how Tesla coils work?

[Prometheus]

Yeap, that's how all transformers, including Tesla coils work.

[Manriquea]

This is slightly incorrect, actually in a tesla coil Faradays law of induction is at work, and it has more to do with the make and break speed rather than the turn ratio.

[puffin_juice]

Thanks for your reply, It really helps my understanding? I guess few coils at high frequency is the way to go if I want to keep the primary compact.

[baburam83]

High frequecy results skin effect in the conductor, making the use the thick wire useless so, the idea of using 1.5KHz is not appropriate, similary in the other the hand to reduce the skin effect if you use thin wire then it again increases the resistance of the wire, thus effecting the primary voltage to become very low, So the frequecy must be selected in such away that it satisfies both the condition for low resistance and desired power efficiency

[NullFlux8ight]

As I understand it, what is happening is what I would be expect. The spinning magnets induce a current in the larger coil(primary). This sets up a doughnut(toroid) shaped flux field. This flux field induces the smaller coil(secondary), which lights up your Led. The reason that the Led is so much brighter is that the secondary coil is encompassed in the primary field as compared to the secondary coil being on the outside which reduces the primary flux fields' boundary.

[duckythescientist]

Allright... I've tried something like this in the past and it didn't work for me either but I'm gonna be a hypocrite anyway and tell you what I think. For the charger circuit in one of the pictures you have the inductor and the capacitor and the AC generator all in series. That is not what you want. You want them all in parallel. In parallel they will draw the least current at resonance. In a parallel configuration the only current drawn will be from the resistance of the circuit and whatever is sucked away by your receiver. Also I believe a better amplifier from your timer in necessary. I would use mosfets instead of regular transistors. I would also use an H-bridge configuration. After all that I would blame a mismatch in resonance. I hope this helps! Ask me specifics if I wasn't clear in my explanation.

[Zorink]

PopSci had an article on this not to long ago.

[thermoelectric]

How could I make something like this to supply 12 volt from a batery through 10-20mm thick floorboards and have a 12 volt output?

[puffin_juice]

Well I cant really give you a circuit. After lots of research I have learned that it is very hard to build IPT without a microcontroller. Its just not efficient to have a set frequency when there are so many variables for example distance and resistance. For this reason I haven't been working on this for a while because I first have to figure out how to program microcontrollers. Sorry that I wasn't more helpful. I would recommend that you do some research on this. I think I did list some of my bookmarks on this instructable which have some good information

[thermoelectric]

What typeof microcontrollers?

[puffin_juice]

Whichever, they all do pretty much the same, the reason why you'd wnat to use a microcontroller is because it is a matter of changing a line of code to change the frequency. You could also make it smart so that the microcontroller automatically sets its frequency to that of the receiver. I dont know much about microcontroller, because I have only just started to look at them. You could try the atmega range. The benefit of starting with a more complex microcontroller is that there are no limits, and you can use the same skills on more advanced atmega products in later projects. So dont use a basic stamp, They just aren't very flexible. Hope this helps, I could send you a introductory document on the atmega microcontroller if you wanted me to?

[thermoelectric]

Thanks,If possible can you send the document to me. I have started looking into programming the ATtiny range but i haven't got very far

[puffin_juice]

I'll post it as a new step in the instructable. OK?

[thermoelectric]

I don't think i'm going to read all that tonight heck

[thermoelectric]

OK, Thanks

[guyfrom7up]

here's another question, what's the best wire gauge? the higher the frequency, the higher "resistance", yet the more magnetic field is created with more windings, but you need higher voltage to push the amps... So what's the ideal gauge size, coil size, volts and amps?

[puffin_juice]

This is a question I don't know the answer to, maybe a bit of research might help you find the answer. But I don't think it really matters. The difference in efficiency would be very small.

[TheNerdGroup]

Hi _{Im new here but i seen this and thought i would chime in. I have found a new form of mutual inductance as a result of my research in the joe newman motor saga} I am founder of The N.E.R.D. Group and i thought you might be interested in seeing my video of this effect happening

I have read faraday's own laws on mutual inductance and you can see it here Laws of Mutual Inductance
and they clearly state
The magnetic flux through a circuit can be related to the current in that circuit and the currents in other nearby circuits, assuming that there are no nearby permanent magnets.
My newman motor works from permanent magnets, so I know its not any standard form of mutual inductance _{but i sure do get a huge back emf and back spike up into the 100's of volts from just 12v input.}

Bill - TheNerdGroupTheNerdGroup

[IgnatiusMonk]

In connection with the previous comment

good waves:
http://www.sc.ehu.es/sbweb/fisica/elecmagnet/induccion/variable1/fem1_3.gif

bad waves:
http://www.sc.ehu.es/sbweb/fisica/elecmagnet/induccion/variable1/fem1_2.gif

[IgnatiusMonk]

It can`t work using an square wave in the primary. Better try an easy to do triangular wave circuit to feed the primary coil. You can use a 555 too. Explanation: the wave induced in the secondary by an square is a tip form wave without no area below it. this area is the power you're transmitting. Otherwise when you use a triangular in the primary you obtains an square wave in secondary. (a perfect wave to rectify and with a big area below the line)

[Plasmana]

Hi, I had built a wireless power project a while ago and it worked very well for me. Its operating frequency was around 2KHz, I am not too sure and the primary coil has 30 turns and the secondary had 1000 turns, the voltage output from the secondary coil was around 100vac

[Leroy]

How can I increase the voltage across the primary coil?

Inductor is another name for a coil. The voltage across an inductor equals its inductance in Henrys times the instantaneous rate-of-change of current through the inductor in Amps/s. The coil's inductance is a fixed property of the coil once you've made the coil. It's the second factor--the rate-of-change of current--you can change. How? -- By increasing the frequency you apply to it.

Do you have access to an oscilloscope? If you do, you can measure the frequency coming out of your 555 circuit, measure the voltage across your coil with a voltmeter, then divide to find your coil's inductance in Henry's. Then, using the same equation, you can figure out what rate-of-change of current you need to get a desired voltage across the coil.

[puffin_juice]

Thanks that clears things up a lot!!!

[glsanch]

I you can reach to produce small amount of energy try to put together 2 or more circuits on parallel to have more power thats own of my theory. why you don't try to use the energy thats already used for transmit thighs like tv or other frequencies only to produce energy, the only thing that may be you need is to receive all the energy in a lot of frequencies and sum all togeter in parallel circuits. Other thing that I think is may bee you nee do increse I (ampers) sorry english is no my first lenguage. but I think the first idea is better put a lot of frecuencys that all ready have enough power and catch all of them togeder in parallel. an maybe this will be enogh energy to use in a wire less charger.

[puffin_juice]

I dont know how much energy is available from air waves at any one time. I dont think its much. Surely you've heard of the crystal radio which uses the energy in the radio wave to power it. Unfortunately this is a very small amount of power. Even if you captured all the waves in the sky you would struggle to generate a useful amount. I could Imagine that it wouldn't be enough to charge a battery, Perhaps a capacitor. It would be cool if someone could prove me wrong! I think it would be fun to try and see how much power you could get by adding the power from different frequencies. Maybe there is an easier way to do collect the power from multiple frequencies at the same time by having only one coil. I might have a look into this once I've got my IPT thing going

[nf119]

If you are using general purpose transistors, the voltage drop on each is around 0.7 V. So on your oscillator circuit you have a transistors so the output is a max 4.3 V and than this drives the H-Bridge where you have two pairs of transistors in a series so there is a 1.4 V drop, that lowers the output voltage to the coils to <3.6V. Plus the bases are only getting 4.3 V not 5 V. Also the transistors may not be able to switch at such high frequency, thus only giving out a weak harmonic. I would just use a simple Wien bridge oscillator with an op-amp. And use two op-amps in variable gain circuit (one inverted, one non inverted) so you can control the output voltage. I believe that a sinusoidal output will also be much more efficient than a square wave. Or if you want to try to savage your circuit, just try amplifying the output with op-amps instead of using an H-Bridge.

[puffin_juice]

I am not actually using the H-bridge. It was one of the circuits I considered using. At the moment I am using a voltage divider and two transistors. The circuit diagram is in step 10.

Oh and I may not have made it clear. I'm not actually running it from the USB port. I'm using a stepdown transformer. From mains to 6VDC, max 800mA.

I had a look at the datasheet of the transistors I'm using. Does this have anything to do with the max switching speed?
High Current Gain - Bandwidth Product -
fT= 2.0 MHz (Min) @ IC
= 500 mAdc

[nf119]

Can I get the values of the three resistors and the N-numbers for the three transistors from the right side of that circuit?

[puffin_juice]

The two resistors in the voltage divider are 3.9ohm, the other is 1kohm. The two power transistors are MJE2955T & MJE3055T and the other is an average BC548 Is that what you wnted to know??? I dont know what you meant by N-numbers

[nf119]

Yea those are the numbers. I think I found your problem.

On your diagram from step 10, you have those two 3.9 ohm resistors across Vs+ and 0V in series. The resistance of resistors in series are additive and thus 3.9 ohm + 3.9 ohm is 7.2 ohm. Using ohm's law, V=IR we find the current:
6V = I * 7.2 ohm
I > .833 Amps
thats over 833 mA

You said your power supply was 6VDC max 800mA, so there is basically a short across the Vs+ and 0V across these resistors. The resistor should be really be hot since 6VDC at 800mA is 4.8 Watts dissipating through these resistors. Voltage dividers are not meant to drive large loads. Their outputs are meant to be amplified.

I think I am gonna do something like this for my ap physics class, so if you want to collaborate PM me your email or IM, I don't usually check my instructables account.

[puffin_juice]

I somehow overlooked that. I wanted a higher voltage across the coil and just kept decreasing the resistances. Thanks, I'll make sure I wont do that again.

[nf119]

Yea. I been thinking about this and I don't think you need a voltage divider. The two circuits (two coils) are electrically isolated so only voltage differences are transferred not the actual voltage values. The receiving circuit will not sense the difference between -3V/3V pulses and 0V/6V pulses, all it sees is the difference (6V). Try the circuit below, you can keep the 3.9 ohm resistor and also the same transistor, put the transmitting coil between them. That should work. I am pretty sure it will.

[puffin_juice]

After a bit more thinking.....does that mean that a rectifier is not needed on the secondary coil....or do we still get a negative voltage when the field dies?

[nf119]

You'll still need a rectifier. The "ground" of an AC single is the average of its voltage over time. So in a square wave (w/ equal length low and high pulses), the ground theoretically is in the middle of the high pulse and the voltage of the low pulse - so there is still positive and negative. Can I ask why you are trying to tune the receiving circuit in resonance? If it was in resonance, wouldn't there be a erratic build up of voltage that will well exceed the voltage of the transmitting coil? I would just rectify the received single and than attach a single capacitor (6V 100 to 200 uF) parallel to rectified DC lines to regulate the voltage during the slight disturbances caused by the switching (between high to low) on the square wave.

[puffin_juice]

Thanks for the explanation. So now that I know that I can pretty much finish it. I'm very excited to announce that it does work, I had 1.7 volts across the secondary and lit an LED. The only reason why the voltage is so low is because I have less windings on the secondary coil than the primary. I know that I can increase the voltage by increasing the area of the primary coil or incresing the number of turns. I could also increase the turns on the secondary coil but I dont want it to get too bulky. Now I just have to find out how I can get others to build it. The problem is that the coil will have over 150 turns ( I know its not like the mouse with its compact coil, but they have some tricky circuitry to up the voltage on a low resistance. well thats not actually physically possible so they must use some other technique). I have to somehow instruct people to construct an identical coil, and thats not easy.

[guyfrom7up]

I think that it's just a simple boost converter inside the mouse, mouses take next to no current, kinda like a tv remote if it's conbtinously on, but you have a continous power source.

[puffin_juice]

Very good thinking. I wish I had thought of that. I'll try it tomorrow. Thanks for your help!!!

[nf119]

ugh I messed up, you need a higher ohm resistor. I think 600 mA is enough for the coil (200 mA left for the rest of the circuit).

6V = .6A * R
R = 10 ohm

yeah use them 10 ohm or higher

[puffin_juice]

lol i made the same mistake as you by using your numbers. lol. I have made these changes and also wound a coil with more turns (4ohms). I also bought an LCR multimeter. Now ill be able to measure inductances and capacitances accurately. I'll update this instructable soon if I make any progress

[alfonso]

Wait, I was reading the comments below, and I would like to build this, but is it done yet? Are the instructions updated? Great instructable so far! + and fave!

[puffin_juice]

No its not complete. I'm still working on it. and as you can see cerincok is doing pretty well. I'm sure that there will be a working circuit on here soon. I cant say how soon but with the help of you guys I haven't given up yet. Thanks.

[TheAirSpecialist]

ok... how do i explain this. you are, as they say (reinventing the wheel) this just simple works like a TRANSFORMER!, yes a transformer, you got a primary and a secondary, you are making a coil which makes and brakes a magnetic field! and your secondary coil would pick it up and create electricity and that is sadly a transformer! if u understood how this worked you could make 1 in like a day!

[guyfrom7up]

bit more complex... it uses RESONANCE to EFFICENTLY transfer electricity through air. A normal air transformer would be much much much more inefficent in this situation.

[guyfrom7up]

I think I know the problem check me back on this, I'm too lazy to read the instructable again, it's 11 on a school night. I'm working on this same thing. I believe the problem is that putting a high frequency through the coil (inductor) is creating a high resistance, not allowing enough current through. For example, lets take a design I'm working on. with a uH of 2915, to allow 2 amps through at 9 volts (i thyink, I erose what I did since I'm changin the design) the frequency must be 265 hertz. I think by using a smaller coil You can fix this. good night!

[maker001]

exactly how far are you trying to transmit the electricity?

[puffin_juice]

pretty much on contact, but the further the better!!!

[skrubol]

I would think your first problem is that big resistor divider network. That's sapping most of your power. You need to get that 4 transistor bridge working. I'm not sure how it would be effecting the functioning of the oscillator, but for the second input to it, you need an inverted version of the first input.

[judtoff]

What about charging a capacitor with the USB, and then periodically dumping it into an inductor. A large enough value cap could certainly deliver enough current into the coil, even it it is a low impedance. If you could get the timing right I think it would be feasible. Also, why USB? Most computers can source over 30A from the 5V rail. All you need is a molex connector...it won't even waste your USB ports! Just a thought. Keep up the good work.

[offlogic]

Here's a [Microchip app note]http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1824&appnote=en011766
on designing an RFID system. Might have some pearls in it.
Good luck!

[cooblades]

I built a device that does exactly this, except for an i-pod. I never packaged the design into something compact. Here is what we used. Target frequency 120kHz transmitting circuit 555 timer oscillator MOSFET trigger (make sure it can switch at a high enough frequency) wound inductor coil (wired in parallel with a capacitor for a natural frequency of 120kHz) receiver circuit 1 receive coil wound and balance with a cap for 120kHz natural frequency 1 radio shack h bridge 1 radio shack 5 volt regulator end product that was all we used and it transmitted about 4 volts and 280mA and charged an i pod

[puffin_juice]

Aw awesome. So it does work. I actually haven't been working on this for a while but want to get a working instructable up that anyone can follow soon. Thanks for your comment

[Aerospaced]

Great project. It's nice to see that so many folks pitched in for you. Remember that magnetism decays exponentially too. I would strongly recommend "Grobbs basic electronics" the perfect text book for all.

[ry25920]

Fave +1

[brokengun]

I've read quite a bit on these and eventually plan on messing with one myself. From what it looks like, I think your just not putting enough juice through the primary coil. I know when I build mine I was told to use a "power transistor," to put more current through the system and make the waves have a larger amplitude. I would look into putting a power transistor on it and also how much power a 555 timer can take, you might need another circuit in addition to the 555 that will beef up your amplitude. It looks good though, I think your definitely on the right path.

[mattccc]

change the freouence to 11khz

[cerincok]

i'm really sorry made you waiting all this time...forgot to post the schematic circuit..I'll reply your mail later...

[technopenguin]

I found this circuit a week ago on edn.com . It utilizes two circuits, a transmitter and a receiver. The transmitter uses a crystal to transmit power at a frequency, while the receiver circuit uses a full-wave rectifier to smooth the received power back out. Look at figures 1 & 2.
Here's the link:
http://www.edn.com/article/CA6501085.html?text=power+transmitter
Hope this helps! Ever since seeing the article, I've been considering trying this out for myself.

[puffin_juice]

Thanks! this is pretty much the same circuit as some of the ones talked about in this instructable. It has all the values. Which is nice. I would like to hear if anyone can get it going

[cerincok]

im preety buzy lately....sorry..this is the image from what i've got...

[puffin_juice]

Hey look at that. You have a similar mouse. I can see that you have the right setup. 5V is the recommended voltage for these mice. If you have the same brand? And I see that the LED is glowing. You Have gotten further than me! Today I thought I should try using the coil from my batteryless mouse. I only managed to get 1.5V after the rectifier on the mouse. I am using a lower voltage. 6.88V. I think I made this instructable a collaboration. If I'm correct that means it can have more than one author. If you would like you could document yours on here too. I just dont know how it works? and how to set it up?

[cerincok]

the circuit diagram is simple....just replaced the load with the coil...

[cerincok]

Hi there.....what about your project progress for now?. Have you finished it? i am really exited to know coz i know this was really great project....I found this and it might be help you a little more... Pulse Controller Circuit
It also uses an IC555 and comparator circuit to generate a pulse signal. It can also be use as a coil driving circuit......MOSFET i think is the best component that produce the efficient switching signal...

[puffin_juice]

I dont know if you saw it, I have updated my instructable. theres a video so you can see what I've actually done so far. And thanks for the link, I had a look, I will probably need something like that if I want to increase the power

[zkbdda]

I am too lazy to go through the whole comments, but I strongly feel that I should help you. I have no idea how far you have come with the help of the previous comments, so if my suggestions seem stupid or if you have already thought of this, let me know.

I don't want to go into the technical details, but here are my suggestions which you can try out easily.

1) The coil might need a higher frequency to resonate. Probably in the megahertz range. (Again, this is just my hunch).
2) The power amplifier circuit I see might not give you enough power. Something looks fishy, but I dont know what exactly.

Try wiring the coil as a flyback convertor, with a simple feedback coil. The circuit will be much simpler and the frequency can be much higher. See the link below for example.
http://www.powerlabs.org/flybackdriver.htm
The transistor in this circuit can be replaced by any decent NPN power transistor. Althought the circuits shown use ferrite cores, it should work with air cores too.

I have to go now, I'll try to add more details as soon as I get home.

[puffin_juice]

I have already seen this. The same principle is used in the camera flash of a disposable camera. Unfortunately its not quite as easy to determine the frequency as it is with a 555 timer

[DonQuijote]

ok. i really have little suggestions about this. i am aware of the theory behind it, i just learned of these things in school last year (although specific formulas and other mathematical gadgetry are missing form my memory), but my practical skills equal the void. however, I'd like to build it, when you fix the bugs. here's another idea, for people that might wanna try it: when you guys have sorted out the bugs with the wireless power transmission, someone might come up with ideas of how to add EXTREMELY short range USB data connectivity to this. i am thinking perhaps at building for example a Pad for my SonyEricsson W300 i, where i can just put it down when i come home, and it should connect through it to the usb port of my computer -> data transfer AND charging. no plugs, no breaking connector holders (people with sony ericsson phones know what i am talking about). how about that?

[puffin_juice]

I'm not a fan of programmable IC's ill leave that to someone else. Of course its possible. The mouse demonstrates that quite well.

[DonQuijote]

ok, but if ANYONE does that, would anybody please mail me? i rarely have the oportunity to check new instructables. e-mail at [e-mail] . thank you

[llamafur]

put a metal plate inside the coil transformers have a metal bar

[firemanfu]

well your a hell of a lot smarter than me already

[puffin_juice]

Not really, I'm a first year uni student. Started this about 3 months ago. You can do anything if you put your mind to it (and you have access to the internet!!!).

[firemanfu]

im 13 and this is the first report card since third grade were i havent gotten at least 1 C or lower, you have to give me some credit though im in all gt classes

[mspitze]

FYI, take a look at this guy's site, I think it will answer your questions.

http://bea.st/sight/levitation/

Mike

[puffin_juice]

Thanks, its hard to find stuff like this because its not used for the same purpose. I'm glad I posted this instructable. It gives you many point of views and ideas. Thanks a lot

[mspitze]

I don't think your USB port could supply enough current to the primary winding. The resistance of your primary winding is very low and probably requires about 1-3 Amps in order to see a substantial secondary current and voltage. I have had luck with this type of circuit when I built a POV clock years ago I do remember my primary current was up there. An air core transformer is not very efficient even at resonance you are limited by copper losses, distance between windings and frequency response. You should be able to select the ideal freq. by looking on a scope while you tune your freq. and duty cycle(should not need to be > 50% duty). If you get 100mA or better your doing good. Multiple smaller primary loops in parallel may give you better coupling as well. Seems as if the pad center is the weakest point.

[puffin_juice]

If I dont have enough power, multiple loops are a good idea. THANKS

[RJSC]

I've noticed that the circuit on the mouse is a capacitor parallel with a coil.
If you want to consider an RLC model consider the Parallel RLC model, not the series RLC model. I don't have the time to think about it now, but it may help.
In a parallel RLC circuit you get the maximum reactance at the resonant frequency.
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/parres.html#c1

[puffin_juice]

Hey thanks mate, Know that you've said it "no voltage at the coil at resonance" my circuit might be working anyway. I have been looking for a voltage to determine wether my circuit works. maybe I should add the rectifier and measure DC current through a resistor. Maybe its already working. Do you know what kind of voltage I can expect from the secondary if the current through the primary is about 200mA and well..the voltage, as you said 0V

[RJSC]

Well... The primary circuit is probably not in resonance, has the USB bus provides 5 Volts and you've measured 8V. The reactance of the coil mus be high. Try to borrow an inductance meter an check the inductance of the primary coil.

[puffin_juice]

Shouldn't the voltage drop be lower at resonance? as the only resistance in the circuit is the R of the LCR circuit?

[RJSC]

If the coil really is low resistance, at resonance there should be no voltage drop a the coil at all. At resonance the circuit works as if there was no coil or capacitor, just the resistor.

[puffin_juice]

Does anyone know how the secondary circuit (set capacitance and inductance) remains resonant even though the mouse has a range of frequencies. *The range of frequencies is to elimininate interference of electronic devices.

[kllrwolf]

Several things to look at. You said you made the primary and secondary coils the same size, but the original seems to have the primary coil to be much larger. The size of the coil does matter. The smaller the coil, the more windings needed to get it to have the same inductance. Also, is the original mousepad have any magnetic properties. If so, it too will increase the inductance of the primary without changing the resistance. I have no clue how to determine the magnetic density. A third thing is the wire gauge. It does not have as big of an impact as the other two. It mostly affects the power handling capability of the coil without overheating. Since you are dealing with inductance, too high of a frequency will cause the inductor to act like an open circuit, thus there will be no voltage through the inductor, causing nothing to work. I am not saying your frequency is too high, but if all else fails, try bringing it down some. For power transfer I recommend keeping it below 1 KHz. the higher frequency does not transmit more power, just makes it easier to generate a cleaner DC signal when it is rectified. Finally, it is hard to tell from the pictures, but it looks like the original secondary coil has more windings than the primary. This is important as well. Having more windings on the secondary would help compensate for the losses that will occur between the primary and secondary coils, as well as increase the voltage of the secondary in relation to the primary voltage. I am sure I am missing other things as well, but hopefully this will give you something to look at that will help you solve the problems and not confuse you. Any more information would require me to find my books for exact formulas and such, which I just packed away since the semester just ended for those classes.

[puffin_juice]

The only reason why the primary coil is a lot larger is because it needs to supply the mouse with power over the area which you move the mouse. However changing the area and number of windings will have a similar effect as it does in transformers; it will change the voltage on the secondary coil. I am guessing that this can be calculated with a lot of tricky maths. Thats how I could increase the voltage.

[Ohm]

How far into the theory do you want to go, I have a few text books with chapters dedicated to transformers. First what are you using to test the voltage on you coil, if it is a VOM it might not be able to accurately read that high a frequency ac signal, you well probably have to use an oscilloscope to get an accurate reading. Also when you test it with a scope disconnect the primary coil and run the signal strait into the scope. If you are getting a correct voltage with the coil off you probably have too high of an impedance coil, you probably need to wind the coil to have a resonant center frequency equal to that of the frequency you are outputting to get the most efficient transfer of power. One thing you can do to determine the correct number of windings is to connect the oscope across the primary windings on one trace and the secondary on another trace and start adding or removing windings from the coil, slowly unwind the coil until the voltage on the scope maximizes, you can also add more windings to the secondary to make it pickup more voltage, again watch on the scope until the voltage maximizes. Hopefully this helps you a little. Its been a while since I looked at this stuff and we did not cover that much of it.

[puffin_juice]

I'm just using a cheap multimeter. I thought it might be giving me a false reading. Damn where am I going to get a cheap oscilloscope. Do you wreckon one of those cheap USB oscilloscopes would work?

[tangoecho]

I always thought that you needed a constant(ish) flux to generate power, which is made from the sine-wave form of the voltage (as a changing voltage produces flux rather than a stationary voltage which produces no flux). Your 555 produces a square wave which only has a sudden change in voltage and thus only a spike in flux when the voltage changes from maxima to minima. Try using a transformed (but not rectified) AC source to test it first.

Or I may be completely wrong and not know what I'm talking about.

[puffin_juice]

I know what you mean, but the current is changing direction at such a high frequency that it shouldn't matter. Plus the change in current is not instantaneous, so we get a steep curve, like a wave almost

[trebuchet03]

Afrotech

I'll admit that I haven't read your entire project (yet)... But this was the first thing that came to mind - not sure if it will help as it is a slightly different concept ;)

[puffin_juice]

Ignore my previous comment, I just found out that the "afrotech" word above your comment was the link. I'm quite impressed

[puffin_juice]

Did you mean to forget to write down the comment?

[nebula]

This looks like a really fun project. I have thought about wirelessly charging things with induction but I never bothered to try.

I am not entirely sure about the theory but maybe a this may help: http://www.evilmadscientist.com/article.php/joulethief
The device steps up voltage using a home made toroid.

Good luck with it!

[puffin_juice]

I thought about using a transformer of some sorts. However this would change the inductance of the circuit and I dont think component specifications give you the inductance

[maker12]

use splash power.

[GorillazMiko]

wow, nice work so far. if i could do this, i would. i need one. badly.

[joemonkey]

nice, i need this. be careful, some one is bound to unpublish and scold you

[sugg22]

good for you - admitting partial defeat but still persevering. nice.