This project uses the module RAK3172 as main controller (no need for AT commands from a host controller). It has inputs, hall switches, motion sensor, external memory and LoRa communication. Targeting small size and low power consumption, it can be powered by a single or double AA cell, solar panel or connected to the mains.

For the SW development I am planning to use the RUI3 APIs from RAKwirelles. Internal connectors are available to connect the ST-Link in-circuit debugger and programmer interface and serial monitors.


The PCB is on the way… under construction.

Block Diagram

Main Functions

  • Alternative power supply options (assembly option), reverse polarity protected:
    Line Supply: input voltage range from 6V to 32V, with a Buck converter to 3.3V;
    Battery Supply: input voltage range from 1.8V to 5.5V, with a Buck-Boost converter to 3.3V;
    Holder for 2 x 1.5V (series) AA batteries, 1 or 2 x 3.6V (semi-parallel) AA batteries for longer autonomy;
    One battery cell (Bat2) can be used as a backup for the Line Supply input.
  • RAK3172 module with an internal uController for the LoRaWAN stack and the application software: Arm Cortex M4 32bits MCU, with 256kB Flash and 64kB SRAM;
  • LoRaWAN communication, Class A, B or C according to LoRaWAN specification 1.0.4, performed by the RAK3172 module. Supported bands: EU433, CN470, RU864, IN865, EU868, AU915, US915, KR920, RU864, LA915 and AS923. Ipex 1 connector for external antenna;
  • Four Digital / Analog Inputs, configurable for High or Low active or 4-20mA sensor signal measurement (assembly option);
  • Possibility to connect the external temperature sensor ds18b20;
  • Two Hall effect switches, omnipolar, push-pull output;
  • 6-Axis motion sensor, IMU (3-Axis Accelerometer and 3-Axis Gyroscope);
  • I2C port for external Temperature and Humidity sensor;
  • 8kbit serial EEPROM for system configuration;
  • 8Mbit or 16Mbit serial flash memory for data logging;
  • Two LEDs for visual interface and warnings.

PCB

FR4, two layers, 75 x 50 mm

03/Jun/2025