A development effort between Microsoft and National Semiconductor Corp. gave rise to the key ICs for the Spot engine. The processor chip (National's MM9662) contains an ARM7 CPU and needed ROM/SRAM and is supported by two 512-kbyte flash memory packages from Silicon Storage (SST39WF400A). National also supplies the custom radio chip (MM9642) receiver along with op amps (LPV321) and low-dropout regulators (LP3987, LP3883). A lithium-ion battery pulse charger (LTC4052-4.2) made by Linear Technology; a Maxim battery monitor (MAX6436); and two Torex voltage regulators (XC6202, XC9801) round out the power-management circuitry. Citizen Watch of Japan was chosen for the module manufacture.
With the rich set of electronics and always-on nature of the device, low-power design was a must given the internal 3.7-volt, 150-mA-hr Li-ion battery. Extending the wireless theme, a clever induction charger is used to ac-couple fresh juice through the hanging watch stand.