Goal: To build a sensor to measure some things!

This project was more about learning things that interest me more than developing a complex product. I wanted to learn more about:

  • Creating a Bluetooth Low Energy (BLE) application from scratch 
  • LiPo battery implementation incl. charging circuitry
  • Antenna design, layout tips and tuning
  • Designing for ultra low power 
  • PCB assembly with stencils and the reflow oven

Still high on motivation I made a sketch of what I was thinking at the time

This was actually when I was considering using LoRa for communication. Of course this ended up being totally different from what I actually made in the end.

Let's break down the different subsystems:


Power management

  • LiPo Battery
  • Battery level detection - maybe voltage based?
  • Charging connector - USB micro B or USB C ?
  • Battery Protection - over current, short circuit, over voltage, over temperature
  • Charging IC
  • Load switch - to turn the sensors off during sleep
  • Voltage regulator


  • ON / OFF - Slide switch
  • User Input - momentary tactile switch
  • Charging LED
  • Status LED - RGB?
  • External headers for other sensors - 4 x male header. Will not mount unless needed. Probably I2C


  • Crystal
  • General MCU implementation - based on nRF52 reference
  • Programming and debugging connector
  • Antenna & Matching Circuit


  • Temperature 
  • Pressure
  • Humidity


Here are some more details about specific parts of the system that I thought were interesting.