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:
- 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
- General MCU implementation - based on nRF52 reference
- Programming and debugging connector
- Antenna & Matching Circuit
Here are some more details about specific parts of the system that I thought were interesting.