SHT21 Interfacing with EnOcean STM300

The package provides all information to rebuild the extension board, and software sample code to develop own wireless humidity & temperature sensor products. It consists of
  • Application Note AN508: “I2C Dolphin interface”
  • AN “SHT21 interfacing with EnOcean STM300”
  • Extension board schematic and assembly
  • Sample code
  • Energy budget calculator
As the SHT21 is powered from 2.1 to 3.6V and STM300 I/O ports operate on 1.8V1, the SCL and SDA
communication lines need to be level shifted. Further, to optimize the overall power consumption, a sensor power switch is implemented with usage of WXIDIO pin. For I2C communication, pull-ups for data and clock line are embedded. To assure stable I2C communication it is recommended not to exceed 130kHz frequency for SCL clock line. A capacitor is used to stabilize the voltage supply close to SHT21.

With usage of the WXIDIO pin and recommended hardware implementation on the extension board, a power switch allows the STM300 module to switch the sensor on and off. As the STM300 module is in sleep mode during the sensor is performing start-up or measuring tasks, the power consumption of the system can be optimized.

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