cross-posted from: https://programming.dev/post/58622590

This project demonstrates how to integrate the Renesas EK-RA4M2 development board with the Renesas CO2 Sensor (RRH47000) and the BleuIO Dongle (SSD025) by Smart Sensor Devices, built on the Renesas Bluetooth Low Energy SoC DA14695. In this setup, the dongle advertises sensor data from the CO2 sensor, including CO2 concentration, humidity, and temperature.

The sensor data is displayed using the RTT Viewer.

Yesterday, I'm building a DIY battery pack out of cells harvested from old laptops, thinking "Man, I wish I knew someone with an old broken e-bike or something".

Very next day. I go for my daily walk. 1 block from my house, e-scooter on the curb, with a sign that says "FREE". "Sold!" I said out loud, and carried the thing one-handed quickly back home (okay I only made it a few houses before I switched to two hands).

The escooter itself was held upright with zipties, rear wheel was present but not attached, rear tire was blown, and while it did power on and show something on the screen, the throttle didn't do anything, and it was physically sticky (and thus very dangerous). And e-scooters are banned in my town (my whole province really), and they're pretty dangerous, and I'm stupid enough to ride without a helmet, so I decided to scrap the scooter for batteries.

I found 30x DMEGC INR18650-26E, rated at 2600mAh at 0.5C, and rated for up to 3C discharge: https://e-foton.pl/userdata/public/assets/Testy_ogniw/DMEGC-INR18650-26E.pdf

I have no use for a 36v series battery pack or its BMS, so I pulled a single cell out of the nickel stripping and threw it in my tester, set for 2A discharge, 2A charge, 5 cycles, 10 minute rest period between:

https://i.imgur.com/egbT45Z.png

I got just over 2500mAh at 2C. Cell only rose ~3°C at end of discharge curve. Cell dropped from 4.1895v unloaded to 4.0250v under 2A, indicating internal DCIR 82.25mΩ. Datasheet states <25 mΩ(ACIR), but I don't have an ACIR tester, however these DCIR values are very good and well within the expected difference.

TLDR: Got free e-scooter batteries. All my testing indicates they are near-new, in perfect health, and quite safe. 280Wh of energy storage, enough to watch old TV episodes on my phone for the first few days of the American Invasion.

https://github.com/yucandu/ClockV3

MCU

STM32L412K8T6

Display

ST7305 168×384 2.9" MiP LCD ("Memory LCD") @ 0.25hz

Sensors

AHT20 — Temperature & Humidity
BMP280 — Barometric Pressure
DS3231SN — Real-Time Clock
MAX17055 — Fuel Gauge

The AHT20, BMP280, and DS3231SN are powered directly from MCU GPIO pins to minimize standby power consumption.

Power System

30 mAh LiPo battery (Bluetooth earbud battery)
TP4054 charger configured for 50 mA charge current
DFM8001 energy harvesting module
Two 30 mm × 30 mm × 3 mm amorphous silicon solar panels
    Recycled from dollar-store garden lights

Runs at ~150uA avg, according to INA228 coulomb counter (used as poor man's power profiler). Sitting upside down on a desk in regular indoor lighting at night, solar panels harvest ~200uA. Coded entirely for STM32CubeIDE.

It was not fun. I learned nothing. But I did beat my old low current hiscore, so that was nice.

Powered by ESP32-4848S040, an all-in-one ESP32-S3 + 4" 480x480 TFT display.

GitHub Link

A tech tinkerer has shared the full plans and resources necessary to build a compact desktop laser engraver. All the resources are available on GitHub, including the components list, 3D printer files, firmware, drivers, and software. Moreover, project creator Elias55745 is selling a fully assembled ‘mini laser printer’ created using these plans for just $64. They also intend to sell everything you need as a kit for self-assembly. However, the store is undergoing maintenance at the time of writing, so the shopping cart isn’t working, and you may see prices in Yen (I did).

GH: https://github.com/El-EnderJ/NeoCalculator

Graphics calculators are one of those strange technological cul-de-sacs. They rely on outdated technology and should not be nearly as expensive as they are, but market effects somehow keep prices well over $100 to this day. Given that fact, you might like to check out an open-source solution instead.

NumOS comes to us from [El-EnderJ]. It’s a scientific and graphic calculator system built to run on the ESP32-S3 with an ILI9341 screen. It’s intended to rival calculators like the Casio fx-991EX ClassWiz and the TI-84 Plus CE in terms of functionality. To that end, it has a full computer algebra system and a custom math engine to do all the heavy lifting a graphic calculator is expected to do, like symbolic differentiation and integration. It also has a Natural V.P.A.M-like display—if you’re unfamiliar with Casio’s terminology, it basically means things like fractions and integrals are rendered as you’d write them on paper rather than in uglier simplified symbology.

Remember tamagotchi? Those little digital pets really took the world by storm for a while, and they're still going to this day. However, unlike the early days of the digital pet, we now have the resources and the know-how to make our own tamagotchis. We can even make them open-source so people can tweak them the way they want.

If you have an ESP32 sitting around and you think it'd be better served as a cute little creature that you need to take care of, then you can do a lot worse than check out this adorable project. While it's still a work-in-progress, it's already at the point where you can take care of a cute critter in your spare time. And when you're busy. And just about all the time.

I didn't set out to avoid official ESP32 developer boards. In the beginning, the DevKitC was my default. It's the board that shows up in every tutorial, the one Espressif clearly intended as a starting point. So I bought a couple, wired them up on breadboards, and started building projects. But somewhere along the way, I realized that what I was buying weren't always official boards anyway, and as I branched out to things like the XIAO line from Seeed Studio, the gap between "official reference design" and "tool I actually want to use" became hard to ignore.

To be clear, it wasn't the price that was the problem for me. Third-party boards from reputable vendors aren't typically cheaper, and in most cases they're actually more expensive. What you're paying for is the stuff around the chip: battery charging, better connectors, basically just a form factor that doesn't fight you.

None of this should come across as being anti Espressif. Espressif makes fantastic chips, and their official boards serve an important purpose. However, these reference designs are for, well, reference. Third-party boards often feel a lot closer to being a finished developer tool rather than a physical manifestation of documentation that an official Espressif board tends to feel like. The base boards are great, but for any project you want to build, a third-party board is likely to suit your needs a whole lot better.