Battery-free activity-sensing smart shoes

  • The Energy Harvesting Controller (EHC) manages charging a power storage device (supercapacitor, or optional rechargeable battery) from a small unstable piezoelectric power source originating in the shoe
  • Analog data from the acceleration and pressure sensors is captured by an extreme low-power 14-bit Analog-to-Digital Converter (ADC) that consumes only 3uA while operating. The CPU performs data processing and analysis.
  • The analyzed data is periodically transmitted wirelessly to a tablet or phone.
  • All energy to run the system is derived from harvested energy.

Management of Device Start-up

  • Harvested energy in extreme low power applications is typically small in magnitude and erratic. Conventional low-power MCU have a relatively high start-up current requirement, not compatible with harvested energy – they won’t power up. The Energy Harvesting Controller (EHC) of the R7F0E manages the energy source interface, and the start-up sequence to ensure robust and reliable start-up while using minimal external components.
  • The R7F0E manages pre-charging a simple external capacitor before initiating the device start-up sequence.
  • The R7F0E continues start-up management by sequencing the power to internal functions to avoid disturbances to its power supply. Separately, The EHC can also manage the charging of a larger external energy storage device such as a supercapacitor to ensure energy is available during peak loads.