Hey everyone! I'm diving into a DIY project where I want to create a temperature and humidity sensor system using the ESP-NOW protocol to send data wirelessly to a central ESP32. I have some background as a mechanical engineering student but I'm still pretty new to electronics. Right now, I'm a bit overwhelmed by all the information out there and the online simulators aren't cutting it for me.
The project aims for a fully wireless, battery-powered sensor that can be discreetly hidden, sending data to an ESP32 that will display the readings on my phone. I'm estimating a battery life of about 30 days using a single 18650 cell, cycling the ESP through deep sleep and active modes to collect data at intervals.
Now, I'm hitting a wall with building a hot-swappable battery pack and figuring out how to monitor the battery percentage to know when to replace them. I plan to use two 18650 batteries: one for active use and the other on standby, switching them once the active battery hits around 3.0-3.2V. For monitoring, I'm considering two INA219 sensors and using AO3400A MOSFETs for safe battery switching. Each battery will have its own BMS protection board, and I'd like to power the INA219 with its respective battery to keep things efficient.
The setup will also power an SHT31 sensor and need a capacitor to prevent reboots during battery swaps. Lastly, I've learned about needing a 3.3V buck-boost converter but I'm unclear where to fit that into my circuit. Any advice would be super helpful—I'm really lost on how to make this all work! Thanks!
1 Answer
For your hot-swappable setup, you should consider using a load-sharing circuit with Schottky diodes, enabling seamless battery transitions. The AO3400A MOSFETs will help manage the switching. Also, place a supercapacitor near the ESP32 to prevent it from rebooting when you switch batteries. After your switching circuit, the 3.3V buck-boost converter should ensure stable voltage for the ESP32 and SHT31 sensor. Remember to exploit deep sleep modes to save power!
I get where you're coming from but I'm not quite sure how to wire it all up either. Specifically, the MOSFETs and their placement before the buck converter have me a bit confused. Any tips on how to set that part up?