Inductive Car Charger-holder for Pre3 With Touchstone

Introduction: Inductive Car Charger-holder for Pre3 With Touchstone

In this Instructable we will create a pivotable inductive car charger for a HP Pre3 phone using a Hp-Palm Touchstone.


  • a few days


  • HP-Palm Touchstone
  • plastic tray from the original packaging of Pre3 (*1)
  • one piece of plastic (around 70 mm x 70 mm x 25-40 mm????????)
  • 3 screws (around ⌀ 2 x 3 or ⌀ 1.5 x 3)


  • sharp blade
  • screwdriver
  • sandpaper
  • glue gun (with high temperature glue sticks)
  • drilling machine (preferably a small one suitable for fine work) or Dremel
  • drill ⌀ 1 or ⌀ 1.5 (it should be a little smaller in diameter as the 3 screws)
  • epoxy resin adhesive (not necessary, but suggested)

As a preliminary note I'd like to point out that the steps that involve cutting apart the Touchstone are only necessary from an esthetical point of view. If the position where you want to place the charger requires that you rotate the Touchstone in some way then the Palm logo will be rotated with the Touchstone and it won't be aligned.

If you happen to be able to position the holder-charger so that the Palm logo is horizontal (or you do not care about the Palm logo), then it is possible to skip the steps 3, 4, 7, 9 and get perfectly working solution too.

Step 1: Cut Out the Plastic Tray

Originally the plastic tray is a big rectangle which accepts the phone in the middle. If you don't want to ever open your Pre3 while it is on the holder, then it is enough if you cut the sides down to the point where the bending is. You should make a cut-out somewhere on the top side (I would recommend the top-right side where the power button is on the Pre3) so you can take out the Pre3 from the holder (it fits very well in the tray and the magnets will help keep it fixed, so you'll have a hard time getting your Pre3 out of the tray without this).
If you think you will slide open the Pre3 occasionally then you should cut some more from the top part of the tray to let the phone open. Measure the middle of the tray vertically, make some markings with some permanent marker. From there start to cut down the wall of the upper side of the tray - 1 mm at a time - and continuously check with the open Pre3. If you reached the point where you can put in the opened Pre3 in the tray so that the upper half of the phone doesn't touch the wall of the tray, then try to open-close the Pre3 while it is in the tray and cut from the walls so much that it doesn't rub each-other. At this point I suppose you have noticed, that the lower part wall of the tray is in the way of your finger to be able to comfortably push-open the phone. So you should cut a part (some 20-30 mm wide and 2-3 mm deep - depends on the size of your finger) from this lower wall.

Finally deburr and sand the edges, keep in mind, your fingers will meet these edges daily.

Step 2: Take Apart the Touchstone

There are some how-to's on the internet (like Palm Touchstone Teardown
Palm Touchstone Hidden USB cable ), but the main thing is there are three screws under the rubber feet. The ring shape rubber feet is put on a harder plastic plate that is fixed on the bottom of the Touchstone with double-sided adhesive tape. So if you can put a blade under the harder plastic, you should be able to cut trough the double-sided tape and take down the rubber-feet in one piece. Or you could cut small holes right on top of the screws.

After unscrewing the 3 screws of the bottom, take care as it gets hold with some small clips so you should take it out by pushing it out from the micro-USB input hole.

There is a printed circuit, that is now loose, you can turn it aside, but take care of the four cables on one side (two thin and two thicker). If you flip it to the side, you can find four screws that holds the aluminium body (the coil and the core) of the Touchstone to the plastic housing.

After unscrewing the four screws the aluminium body gets lose from the housing, but the thin cable is still glued to it with some white glue, so carefully take out the big block and take out the coil on the end of the thin wire making sure that it doesn't get bent of broken.

The housing of the Touchstone still holds the four magnets in place with some glue. Get rid the magnets of the white glue and take out all the magnets. The magnets have some cloth pads on the back side, depending on the final measures of the charger you should remove these pads, but maybe they can fit in there as well. These magnets are really strong ones, so take care that they can snap together really easily.

Step 3: Cut the Top Off of the Touchstone

With a small flat-head screwdriver pop off the ring from the top of the Touchstone. It is fitted with lots of small clips so you have to go around for each one. We won't use this ring, so if you want you can even break it down.

With a sharp blade cut down the top of the Touchstone. There are some small gaps (tenth of mm wide) that were hidden by the ring which we removed, so my solution was to put the blade in one of these opening and start cutting from there really carefully. It should be cut down right under the top, so as close to the top plane as possible, so there you don't loose any height (the magnets are placed right on the top of the Touchstone, so if you cut too deep in the side of the housing, then the magnet will stick out and you'll have lot's of trouble in the end). We will use the middle part with the logo of this top, so if the edge gets damaged, that's OK, but take care to not damage the center.

While you cut the top off, you have to cut the houses of the magnets too, there you should aim also for the smallest loss of height, but 1-2 mm is ok, since it still has some material so at the end you can still glue the magnets back to their place.

Finally do some more finishing/sanding to level up the top of the housing and deburring, so there remains a relatively smooth surface (the plastic tray will rotate very close to this edge, so if it has some sharp places it could cut trough the plastic tray with time).

Step 4: Fix the Detector Coil to the Base

The coil that is on the end of the thin cables should be glued to the core so that it doesn't have the chance to swing or move at all. This should be done so, that no glue should get on top of the coil because than it would get in the way of the logo plate.

Step 5: Create the Holder Ring of the Tray

This is the toughest part. I turned a piece of plastic with a friend of mine who had the needed machinery. Maybe if you happen to be lucky enough then a tube will do mostly for you. The turning was made so that a small groove was created on the inside (as you can see on the blueprint), this will accept the small screws to keep the holder ring in place. The width of this groove should be a little bigger than the screws which will get into the side of the housing so they couldn't jam in, but no wobbling occurs. The depth of the groove should be at least 1 mm, but it can be more depending of the thickness of the material of the holder. When you should create the groove depends on the material from which you create the holder ring. If it is soft, than the groove should be made first, maybe strengthening the ring from the outside while creating the groove to not let it bend. If it is a hard material, than it can possibly made later, maybe even after creating the shape of the tray in it. This is important, because if you have made the groove, you should measure everything else relatively to it, but if you are able to leave it to the end, than you can freely cut the material to create the shape of the tray and afterwards create the groove relative to that.

Step 6: Create the Tray Shape Cut-out of the Holder Ring

To be able to fit on the back of the plastic tray, the holder ring should accommodate the special shape of the tray. First I made a rough sketch on both sides of the holder ring and started to cut with the blade. After lots of cutting and trying, when the holder ring followed the shape of the tray came the time for sanding. At some time I even used a Dremel to be able to speed up the procedure, but warning, if you're not careful enough, you can screw up the previous half/one work hour.

The trick with this holder ring is that the Touchstones shape isn't absolute cylindrical, it is a little bit conical, the base of it has a little bit bigger diameter. So the holder ring has to adapt to this shape a little bit, because other ways the ring will tighten on the Touchstone. Creating this special shape needs some (or a lot of) sanding and probing. This probing should be done in a manner that when you put in the housing of the Touchstone into the ring, the top of the housing should be level with the lowest part of the tray shape of the ring, and in this position it should not tighten on. You should be able to easily turn on it.

The bottom of the holder ring should be cut at such length, that it shouldn't extend further than the bottom of the Touchstone housing. But this can be done even as the penultimate step when all the other parts have their proper sizes and all the screws have their place.

Step 7: Check the Magnets Back to Their Place

You should put together the Touchstone (without the screws, only snap it together). There you should check whether the middle of the core doesn't stick out from the top plane of the TS. Actually if everything was made well, it should be some tenth of mm deeper. Now you should put back the magnets in their holders. If you were really successful in cutting only the really top of the magnet housing than there should be some small plastic bars in the middle of the magnet housing which wouldn't let you put the magnets back, only from the bottom side, so you would need to put in the magnets before the aluminium body. I was that successful too. Now this makes your life a little harder because it is hard to put the magnets in to their places and put back the aluminium body without the magnets clashing together. But it can be done. If you weren't so lucky, or you decide, that those small plastic bars should go, than you could cut them out, and put the magnets in from the upper side.
You should check that the aluminium core and the magnets are still level (or something below) with the top plane of the TS. The point is, these parts shouldn't stand out as it would collide with the plastic tray, but shouldn't be too deep (to far away from the plane) because the inductive charging depends really on the distance, so the further you move the parts from each other the less power will get trough, and after a given distance (a few mm's), the charging will be impossible.

Step 8: Drill the Holes of the Screws That Will Hold the Ring and TS Together

Take the TS apart, take out even the magnets and measure the distance between the middle of the groove on the inside of the holder ring and the lowest part of the tray shape of the holder ring. The distance of the middle will be used to create the holes on the body of the TS. If you're unable to measure the middle, than measure the distance to the closer edge and the width of the groove and calculate the distance of the middle.

DISTmiddle = DISTcloseredge + ( WIDTHgroove / 2).

Pick three points on the housing of the TS (more or less equally placed around) and mark the previously measured distance on it. The point is that you should possibly compensate for the possibly protruding magnets and the thickness of the glue that will hold together the tray and the holder ring. The three points should be chosen so, that you can have access to them with the screwdriver from the inside in a rather perpendicular angle to the housing of the TS. You should drill a hole for each three screws. The hole should be the same diameter or preferably a little smaller than the screw. The point is the screw should cut it's way through the plastic and it should be quite tight. After drilling, the outside of the housing should be deburred and after screwing in the screws, you should make sure that there remains no burrs on the outer side.

Normally when the screws aren't fully screwed in, then the aluminium body could hit the head of the screws if you try to put together the TS, so if you have the holes prepared, then you should take out the screws and use them only at the last tests.

Step 9: Glue the Magnets to Their Place

Glue the magnets into their holders, using the glue gun mainly from inside the TS housing. Before gluing the magnets, you should make sure that you wiped (with some spirit, or other solvent) any fingerprints from the magnets, this way the glue will hold much better. You should press in the hot glue between the magnet and the wall of it's housing, possibly putting some on the bottom of it (the side which will touch the aluminium body on the inside), but not too much, as then it will keep away the body from it's proper place. Take care not to let any glue on the top of the magnets (the side which is facing the plastic tray) as it will keep distance and possibly confine the movement of the tray.


Step 10: Glue the Tray and the Holder Ring Together

Hold the tray and the holder ring together and put it on the TS (you should snap it together for this as the core gives the center of the TS). You should position the tray on the ring so that it is centered to the core of the TS. Mark this position on the back of the tray (around the holder ring) with some permanent marker. Take the tray and do some sanding around the marking so the glue can stick there better. Do the sanding on the holder ring too. Put some glue on the holder ring and put the tray on it centering it properly. Let the glue work as long as it needs.

Step 11: Glue the Palm Logo to the Core

The top of the TS that we cut down holds the Palm logo, so for an added fancy factor (and to hide the core of the coil from curious eyes) we should put this back to it's place. Cut out a circular piece from the top that is some 1-2 mm bigger in diameter than the hole in the tray. You can take as help the two rings on the backside of the top, if you leave some 1-2 mm over the outer ring, it will fit the hole of the tray. Put it on the core on top of the coils properly centered. Take care that it shouldn't protrude from the top plane of the TS.

Glue it there with some hot glue at least from two sides, but better from all four. Watch out for the planned topside of the whole charger, because now is the moment to align the logo horizontally. If you're planning to put the TS in a normal orientation then it's easy, but I had to rotate it some 60-70 degrees clockwise to provide the best viewing angle from the drivers seat, so I had to make some tests for the best orientation.


Step 12: Put the Whole Thing Together

Put some silicone grease or some soap on the inside of the holder ring so that the TS will slide on this instead of rubbing the two surfaces together. Some silicone grease or soap should go into the groove too, so that the screws wouldn't erode the groove.

Put the holder ring with the tray on it on the housing of the TS. Screw in the three screw so that it will hold the ring but it wouldn't tighten up. Put in the aluminium body and screw it in with the four screws in place. Put the circuit on it and the backplane too. Screw in the three screws to hold everything together.

Step 13: BONUS: Put the Whole Thing on Some Holder Plate

A few years ago I had made a holder plate from stainless steel which used to hold my THB Bury car holder for my Treo 650. The size of this plate was perfect for a TouchStone, so I had to only make three new holes for the three screws holding the backplane of the TS and buy three longer screws and three washers. I took the layout of the holes on the backplane of the TS with a thin paper and a pen, marked the place of the holes on the holder plate and drilled them. (take care of the way you hold the paper when you mark the holes, I flipped over accidentally and had to drill a fourth hole, because the holes aren't simmetrical).

Take care not to over-tighten these screws as they are tightened into aluminium, which is not that hard to withstand really big forces.

Maybe you could put back the rubber feet of the TS so that it gives some extra grip and extra shock absorption, but I dig mine so well away that I couldn't find it when I put the whole thing together, so mine goes without it for almost 2 years.

Step 14: Remarks

  1. I was using the German Pre3 versions packaging, which contains a plastic tray which fits the form of the Pre3 perfectly. As it turned out the AT&T version didn't contain this plastic tray it had only some cardboard cut-out.
  2. I was using hot glue gun to put together the whole thing. After one year, on a really hot summer day, some of the glue melted and glued together the plastic tray and the TS so the plastic tray stopped turning. So you should definitely use high temperature glue sticks.
    Or alternatively you could use some artificial resin based glue that will fix the thing once for all. Maybe first time glue sparingly with hot glue gun and if everything is perfect, than go over it with some more serious glue, and if you want maybe you can get rid of the extra hot glue with a hot air pistol (there are lots of plastic so take care not to overheat).
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