07/09/2010, 09:30 PM
I wanted to install the Touchstone in my car, but the location where I wanted to put it (over the ashtray) had no clearance for the USB cable, and besides, I wanted a cleaner look.
The modifications detailed here will allow you to permanently and cleanly mount a Touchstone in your car, and are only intended for those experienced with soldering and electronics. Opening your Touchstone WILL void the warranty!
You can use this mod anytime you'd like a Touchstone to work without the special Palm charger and/or mount with out using a Micro-USB cable sticking out the back. I found that after step 7, I was able to plug the Touchstone into a USB port on my Laptop and it began charging my Pre, whereas before this didn't work. Note that not all USB ports can handle the Touchstones 1 amp draw, so YMMV.
Here are a few pictures of the final result in my car:
Some Touchstone facts:
It needs 5.0V minimum at about 900-1000ma. Preferably 5.1V which is what the Stock Palm power supply puts out. It drains about 50ma when idle (bounces from 20 to 120 as it looks for a phone). You do NOT need a stock Palm charger or USB cable for this mod, only a 5V supply that is capable of 1A and will not sag under load. If the input drops below 5.92V, the Touchstone will stop charging. I do not recommend a Linear regulator, as it will get HOT when it tries to burn off close to 10 watts! I used an old Nokia adaptor rated at 1A and 5.1V. I removed the original cigarette lighter plug with a bandsaw so the unit fit into the ashtray which I mounted my Touchstone over. There was a convenient +ACC line nearby for the Heated Seat switch that I stole power from.
You should be sure to hook the Touchstone power supply feed to the +ACC line in your car, otherwise if you hook it to +BAT, the over 1/2W idle load will discharge your car battery pretty fast! Also be sure to hook a fuse up or use a fused circuit, being careless with a car electrical system is a big mistake!
How-to in 10 easy (sorta) steps:
- Use a hair dryer to gently and evenly heat up the back sticky polymer material. Once warm it should peel off with some care.
- You should see 3 small phillips screws. Remove them and put them somewhere where they will not get lost.
- Remove the back cover by carefully poking a screwdriver in the USB area and pressing toward the back.
- I unsolder the 4 connections to the front half, they are in a group towards the bottom right (as viewed with the Touchstone upside-down).
- Carefully pry the PCB out. Mine had white silicone globs in either corner holding it in.
- Locate R5 and R52. They are near the Microcontroller (large square chip with 28 pins-- Refer to first Pic below).
- Solder a blob between the resistors as indicated in the picture. This will bypass the OEM Palm charger detection, enabling the Touchstone to work with any 5V supply. Replace the board and re-solder the 4 wires leading to the front. I advise a test at this point.
- Solder a relatively fine gauge set of wires to the pads indicated in the second picture. (below) I used a red and black #22 gauge stranded.
- Drill a hole in the back of the bottom cover over the location where you soldered the lead wires, feed the wires through and re-assemble the back cover with the 3 screws (you didn't lose them, right? =).
- Mount the unit in your car. I used a square of 3M VHB tape instead of the stock sticky polymer, as it has superior adhesion. I then carefully trimmed a piece of black contact paper to cover the (now upside-down) palm logo.
Note: It's very important you observe correct polarity, and DO NOT connect direct 12V to the Touchstone, or it will be destroyed! I am not responsible for any damage, nor will Palm honor any warranties once you crack the case.