today more and more smartphones support wireless charging, whether it's out-of-the-box or via an available hardware upgrade (special back cover). but there is no reason why all other USB charged devices shouldn't enjoy the luxury of wireless charging.
in this instructable i'll show you how to add wireless charging capabilities to your smartphone (demonstrated on a Samsung Galaxy S II) or practically any USB charged device (of course i can't guarantee that it'll work on any device but i see no reason it shouldn't, unless there's some other patent or technology preventing it).
Step 1: background and clarifications
*** FOLLOW THESE INSTRUCTIONS AT YOUR OWN RISK ***
take safety precautions and do not do anything you are not certain of.
i cannot be held responsible to any damage you may cause to your device or to yourself !
(now, after i covered my ass, we can begin)
there are a few projects similar to this one on the net. I've drawn ideas from everywhere and incorporated some of my own.
the whole concept and basic design is based on Palm's technology (although there are other manufacturers offering similar solutions). the Touchstone is a Palm charging dock meant for the Palm Pre smartphone, which supports wireless charging via a separately sold back cover.
there are a few wireless charging technologies made by different manufacturers that all rely on the same physical concept but they are not cross-compatible, you cannot mix coils and docks (I've tried).
i will not bore you with the physics behind the concept (although it's quite interesting) and there's nothing i can write that's not already available with more professional descriptions on the net, so if you want you can google "wireless charging" and read all about it.
Step 2: gather the components
the components and tool needed for the job :
1. a Palm Touchstone - about 15$ on Ebay
2. a charging coil - about 8.50$ on Ebay
. adhesive copper foil
4. a small piece of thin gauge wire
5. a >1000mA USB charger (doesn't have to be original Palm but the cheep chinese ones don't seem to work, i'm working with a 2.1A iPad charger) and USB cable.
6. a case \ back cover \ extended battery cover (w\o extended battery)
7. soldering iron and soldering accessories
8. multimeter (we'll need the volt meter and continuity meter in particular)
9. screwdriver that fits the screws on your device.
10. insulating tape
11. wire stripper and cutter
Step 3: see that everything works and make mods if necessary
before you start dissecting your phone make sure the components you got work.
first plug the touchstone to the charger and place the coil on top of it with the metal sticker on top of the coil.
measure the voltage between the contact points of the coil, you should get between 5.2v and 5.5V.
this doesn't mean that your phone will charge - there's a trick (this was a piece of information that was hard to find) :
the touchstone apparently only works with "fast charge" capable chargers. the indicator for this is a short between the 2 and 3 pins of the USB cable (the + and - data pins) so make sure your charger can supply more than 1000mA and you'll need to sacrifice a USB cable for this - take a USB cable and remove it's outer insulation leaving the wires intact. (no need to cut the cable although its fine too)
cut the green and white wires and expose their tip. twist them together and solder (this needs to be done only on the touchstone side, no need to shorten both sides)
close everything up with tape
note that the cable is much more delicate now, you might rip it if you yank it.
note also that some chargers just wont work (I tried with a 1$ chinese charger that's rated at 1000mA and it just wont charge - while direct connection to the phone works perfectly) try and use quality chargers, for your battery's sake too.
see the photos for a detailed pinout of the USB port, it can also be helpful in the next steps as i will not refer to specific pins but to their use (ground and +5v in particular)
Step 4: know your device
disassemble your device carefully (if you're not sure, there are a lot of disassembly tutorials for almost every device out there) and identify the +5V lead on the USB port and follow it to a comfortably solderable spot (unless you are super skilled and equipped and can solder a single micro USB pin) don't worry about the ground lead, every piece of metal in there is grounded.
in my case (galaxy s II), disassembly wasn't hard, 7 screws and a pry tool \ pick \ fingernail and it's open.
finding a place to solder was a little more challanging, it needs to be a place with enough room for the wire and not too small and delicate for the soldering iron to burn or damage.
i used the capacitor shown in the pictures (i had a little help from google and a multimeter finding it).
after you found your soldering spot, try and find the best path for your lead, it has to connect the + from the coil to the + on the USB.
in my case. i chose to work with copper foil because there's just no room for a wire running along the side and the copper foil is relatively easy to work with.
the main consideration for me when choosing the path was that i wanted the phone to seem (almost) unaltered from the outside and for all the separate parts to stay separate (i didn't want a wire or something permanently connecting the board and the cover).
finding ground :
pretty much every piece of exposed metal should be grounded.
you can check with a continuity meter to see whether a specific piece is grounded or not.
it does not matter what it is you're connecting to, as long as it's connected to ground.
choose the piece that will make your design as simple and as neat as possible.
if no grounded piece of metal can be found you can connect to the USB port ground pin.
Step 5: choose your weapon
the choice of conductive material is crucial. not so for performance but for your device to close properly. smartphones and electronic devices in general get more and more compact with more and more technology inside, which means less "free" space. that is our main challenge.
because of this i recommend using adhesive copper foil, i found that the adhesive is quite strong but non-conductive (duh..) so just placing one piece on top of another is not enough to close the circuit. that means there are two ways to go :
1. doing it all with one long piece. this method is harder because you need to carefully fold and flatten the foil without layering too much foil and without tearing the foil, which i found was pretty delicate.
2. using multiple pieces and soldering them together. while this method might be a little easier and doesn't require super fine motor skills you still need to be careful not to use too much solder and not to heat the area too much and melt your device.
of course you can use thin gauge wire if it fits.
using copper foil creates another problem - it doesn't have any insulation. my solution is just using insulation tape. one layer shouldn't be too thick. you can cut the insulation tape to shape and choose what area you want to cover (something that is much harder when using insulated wire.
Step 6: start taping (or wiring)
you can see from the photos that my system consists of 3 separate parts that together connect the leads. i did that because, as i mentioned earlier, i wanted all separate parts to stay separate.
on the device itself - a wire connects the + on the USB (via the ceramic capacitor you can see in the photo) to a copper foil that serves as the contact for the next part.
on the back housing - a (single) copper foil running from the top of the speaker (that is the contact that connects the former part) to the top right corner of the battery compartment - this is the only part visible outside the device and this will be the contact for the next part.
on the back cover - a couple of copper foils running from the leads of the charging coil to their corresponding contact points (the piece of foil sticking out of the battery compartment and a grounded plate which holds the SIM card in place - that's our ground)
it really doesn't matter how you do it, just make sure the device closes back properly and that you are not shortening any circuits.
Step 7: plan A - fitting the coil under the back cover
plan A implies that there's a plan B. well, there is.
i decided to show you this failed attempt at fitting the charging coil and its circuit under the battery cover because it might be relevant to other devices and even the same one with the extended battery cover.
it appears there is just no space whatsoever between the battery and the cover, not even for the coils circuitry.
placing the charging coil isn't that complicated, just make sure there's room where you place it and that you do not shorten any circuits (the coil and its circuit are fully exposed.
the more complicated part was placing the little metal discs correctly - i came up with an easy solution :
take the cover and coil and place them on the magnetic dock.
the coil might not magnetize well but it should be enough for it not to move too much.
now take the metal discs and place them at the four corners around the coil, they will jump into place thanks to the magnets in the dock.
move the cover around so everything is aligned correctly - the discs should slide on the cover and stay in the same place relatively to the dock. see that the coil is centered between the discs.
take the metal sticker that came with the coil and place it on top of the coil (crucial for it to work)
hold the discs in place with insulating tape.
now you can remove the back cover from the dock and use the copper foil to close the circuit and make the contacts.
Step 8: plan B - discarding the battery cover and using a simple case
well, plan A went up in smoke, unfortunately. (i wanted to use an aluminium bumper as protection for my phone but that means using the original back cover)
plan B is using a plastic case without the battery cover. this is not ideal (especially with the case i chose) but it works.
if i could find the galaxy s II extended battery back cover (without the battery) for sale that would bring us back to plan A (if you know where i can get one - please share)
well the attempt at plan A did most of the work for plan B, because everything is held together with tape i can just peel it off and move it to the case.
the only thing left is to make sure there's contact. the case has more space between it and the phone (when the back cover is removed), that means more space between the contact points.
what i did to address this was to fold some copper foil and solder it to the contact point to fill the gap. this was not enough so i just filled the remaining gap with solder. (see photo)
Step 9: close everything up and troubleshoot
close everything and try to charge.
if it's charging - your done.
if not; try these steps :
1. if there's no sign of charge check your contacts. make sure you have a closed circuit. use a continuity meter.
2. if the charging sign is turning on and off there might be a problem with the charger or the cable, try different chargers or check the cable mod.
3. if your wiring passed under or over any components that also have contact points (like the speaker on my galaxy S II) check that they work, you might have created a gap between the contacts - that's what happened to me with the speaker, opened the phone up and bent the contact springs outwards slightly with a flat screwdriver. works perfectly now.