Use Your Evo 4G With a Touchstone Charger




About: Just a guy who likes building things for my family.

This Instructable is to show you how to add inductive charging to you HTC Evo 4G phone without voiding the warranty.  Your phone will remain unaltered.

Basically what we are going to do is take a Powermat inductive charging back cover for the Evo and replace the inductive charging coil with one out of a Palm Pre Touchstone charging cover.

I had a Palm Pre a few years ago and one of the best things about it was the Touchstone charging system.  Since I still had these the only cost was the Powermat back cover and a little time.

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Step 1: Parts, Materials, and Tools Needed


There are only a few items needed for this project.
  1. The phone you already have.  In my case, this is an HTC EVO 4G.
  2. Palm Pre phone Touchstone phone cover.  These are easily found on Ebay
  3. Powermat Receiver door (back cover) for your phone.  These can be found on Ebay or at the Powermat web site at  If you buy one on Ebay, make sure that the one you get has the plug that connects the back cover to the phone charging jack.
  4. Touchstone charging base.  I have one at home, one in my car, and one at work.  These are easy to find on Ebay as well.


The tools I used on the project were as follows:
  1. Soldering iron
  2. Dremel rotary tool although a sharp knife might work for you as well.
  3. Volt Meter

NOTE: If you plan on using any tool for a project please make sure you are familiar with the tool and all of the dangers associated with it. If you are not familiar with a tool then you should ask someone who is to show you the proper way to use it. A lot of communities have classes at local colleges on the proper use of tools and machinery. There are also local woodworking clubs that offer classes at very reasonable rates for beginners. I highly recommend using these resources for your safety and for the most efficient use of the tool.

Always wear eye and hearing protection.
Always work safe with the proper safety equipment and guards on your tools.

Step 2: Romove the Coil From the Palm Pre Phone Cover

The first thing you need to do is carefully remove the induction coil and 4 round metal buttons from the back of the Palm Pre back cover.  This is held down by some really sticky material.  I used a razor blade to get under the plastic and peel it off.  The 4 metal buttons may or may not come off with the cover.  If they don't peel off with the inductance coil then take them off of the back cover and stick them back to the piece with the coil.

Step 3: Romove the Coil From the Powermat Phone Cover

Peel off the heavy protective cover from the coil on the Powermat charging back cover.  This will reveal the Powermat inductive coil.  Pry this out of the back cover to leave a recessed area where we will place the coil from the Palm Pre back cover.  Disconnect the wires from the charging coil board as we will connect these to the Palm Pre inductance coil.

Step 4: Replace the Coil on the Powermat Cover

Set the coils from the Touchstone charging back cover into the Powermat back cover.  You will need to remove some of the thin plastic reinforcing webbing in the Powermat cover in order to get the metal buttons from the Touchstone charging coil to sit flush on the back.  This will help the Touchstone base magets hold it in place.

Step 5: Make the Connections

The wires that used to go to the old Powermat coil now go to the Touchstone coil. The red goes to the negative and the black goes to the positive. It seems backwards, but that is how they wired it.

Solder the wires from the Powermat back cover to contacts from the Palm Pre Touchstone charging coil.

Step 6: Put the Cover on the Phone

Now you can put the cover on the phone and start charging it the easy way.  It is great to charge your phone with this system.  One of the great things about it is that you can position your phone vertically or horizontally on the charger.  It works great if you have you phone set to keep the screen on while it is charging.  You can keep your screen on with your email open.

Have fun with the Instructable and enjoy "hands free" charging.

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    5 Discussions


    Reply 7 years ago on Step 4

    I tried the powermat back with the touchstone base and could not get any voltage out of it so I just replace it. I hoped it would be that simple, but it wasn't.


    Reply 7 years ago on Step 4

    Ok so using the powermat induction charger with the Palm coil may not work.