Palm Touchstone Charger Teardown
The Touchstone charger was sold with a special back cover as an accessory to the Palm Pre. The combo debuted for $69.99 USD at launch. It was one of the first commercially-available wireless charging setups for a smartphone. Due to Palm's acquisition by HP, then TCL, not much original information or documentation is still widely available about the Touchstone.
The Touchstone charger utilizes magnetic inductance, or electric current produced through a loop of wire in the presence of a magnetic field, to charge its internal battery wirelessly. The accompanying back cover houses the companion wire and four magnets that help to properly align the phone when placed on the charger.
The magnetic field generated by the base unit turns on and off rapidly, generating a magnetic pulse that is carefully tuned to the dimensions of the wire coil inside the back cover of the phone. This oscillating magnetic field induces a current inside the phone, allowing the battery to be charged.