Greetings! I wanted to share a personal project I've been slowly iterating on for the past 8-ish months.
This is Meshlet! It's a tiny little node based on the RP2350, which I designed to be deployed just about anywhere. You can throw it in a box outside with a solar panel and take advantage of the MPPT-like charging, turn it into a handheld communicator, leave it on a windowsill hooked up to a BBS script - whatever you want! Standout features include:
- USB C input, with a configurable charge rate limit (250mA, 500mA, 1A)
- LiIon/LiPo and LiFePO4 support
- ESD/TVS protection
- Combination DC & MPPT-like solar input
- Automatic recovery from a brownout on solar power
- Status/charge/power LED disable jumper, added with enclosed solar builds in mind
- Combination JST 2.0 & Picoblade 1.5mm battery connector footprint, so you can pick & choose depending on what batteries you've got on hand
- ~28mA idle current draw (with WiFi disabled)
- Built-in INA3221 for battery, external power, and full-board power consumption monitoring & telemetry
- Built-in BME280 for temperature & humidity monitoring
- Up to 8MB onboard flash
- MOSFET-driven external notification pins for loud buzzers & bright lights
- Optional WiFi support with a Raspberry Pi RM2 footprint
- Total footprint size of ~42*32mm, less than half the size of a credit card!
The board itself is my first ever 4-layer PCB design! I learned a lot about the importance of having unbroken ground planes as return paths wherever possible, especially when working with high-frequency designs. Revising the board was also a fantastic lesson in minimizing unnecessary parts (i.e. duplicate pullup resistors/etc) and managing/optimizing power consumption & delivery.
As for actual real-world use, I've had one running in a solar enclosure off a cheap little 5V panel and 3000mAh battery for the past few months, and it never dropped below 40% despite the gloomy Canadian winter weather. I've also been carrying one as an everyday use node, and have been running a third installed in a cheap solar garden light for around a week to test out the LiFePO4 support, and I haven't suffered a single failure, brownout, or unexpected reset so far on any of them! I'm extremely happy with the stability of these things.
This was a very self-indulgent project, so I don't sell these or have any available to buy, but the whole project is open source and available on GitHub! I also need to give a massive thank you to PCBWay for sponsoring this thing, it wouldn't have left the prototyping phase without their support & and the opportunity to lean on their PCBA services. Always super happy with the end result and build quality. I'm very glad to be able to finally share this project now that all the little bugs and issues from the first few revisions have been ironed out!