Mysterious Files PH

Many HVAC systems in North America operate off 24V systems, which can be readily upgraded with off-the-shelf  smart thermostats quite easily. However, there are many people living in buildings with 120-volt fan coil units who aren’t so lucky. [mackswan] is one such individual, who set about building a smart thermostat to work in these situations.

The build is based around an ESP32 running ESPHome firmware. It rocks a 2.42″ OLED screen with automatic brightness adjustment for showing temperature and control parameters. There’s a rotary encoder on the front with an integrated button for control, with [mackswan] building the physical device to look as clean and neat as possible. The device uses a relay to switch the fan coil system on and off to heat or cool as needed, with an SHTC3 temperature and humidity sensor used to monitor current conditions in the home.

If you’re in an apartment building or live in a condo with this kind of setup, [mackswan’s] build might be just what you’re after to improve your HVAC control. We’ve featured plenty of other DIY thermostat hacks over the years, too. Meanwhile, if you’re finding creative ways to better heat and cool your living space, we’d love to hear about it on the tipsline!

As we learn more about all the nasty stuff floating in the air, it becomes more compelling to monitor the air for pollution levels. [Aleksei Tertychnyi] does just that with pollutagNode2, a solar-powered pollution sensor.

The device uses a Seeed Studio Wia-E5 module for its built-in LoRa low power long-range communication capabilities. Pair that with a cheap 2 watt solar panel and a Li-ion battery, and you have a monitoring device that can stay up indefinitely — or until harsh weather gets the better of it. Even if the solar panel were to be omitted, a full charge would last you about two weeks!

It comes on an open-hardware PCB; no need for giant wire messes, just solder the solar panel, battery, sensor, and anything else you want onto the convenient pads on the side. It also integrates into the existing sensor community nicely via existing LoRa infrastructure. All this combined makes it easy for anyone to deploy one.

If you have a desktop 3D printer, you probably want something to hang filament spools on. [LVTRC] has a spool roller that fits the bill. It also incorporates a scale and a round touch screen. (Google Translate)

We’ve seen those round screens before, and now we wonder why we didn’t think of this. The GC9A01 display shows a progress ring and lets you save settings or calibrations to EEPROM. An Arduino Nano provides the brain, and the load cell connects to an HX711. The project is made to fit a specific printer, but it should be little trouble to adapt it to a different printer or to mount it in an external mount.

One of the calibration steps, of course, is to program the weight of an empty spool to subtract from the total weight. The device can store up to five specific profiles.

Not the biggest spool holder we’ve seen. We keep thinking that we don’t know why we want a circular screen, and then someone always drops in to show us another thing we didn’t think about.

Some people learning the noble art of electronics find the jump from simpler tools like Fritzing to more complex ones, such as KiCAD, a little daunting, especially since they need to learn at least two tools. Fritzing is great for visualising your breadboard layout, but what if you want to start from a proper schematic, make a prototype on a breadboard and then design a custom PCB? Well, with the Kicad-breadboard plugin for (you guessed it!) KiCAD, you can now do all of this in the same tool.

Originally designed to support EE students at the University of Antwerp, the tool presents you with a virtual breadboard with configurable size and style, along with a list of components and tools that can be placed. A few clicks and parts can be placed on the virtual breadboard with ease. Adding wires is the next logical step to make those connections that operate in the horizontal dimension. Finally, assigning power supplies and probe connections completes the process. It’s a simple enough tool to draw stuff, but drawing a layout is no use if you can’t verify it’s correctness. This is where this plugin shines: it can perform an ERC (check) between the schematic and the breadboard and flag up what you missed. Add to this that you can also perform an ERC at the schematic level, before even thinking about layout, and it’s pretty hard to make an error. Now, you can transfer this directly to a real breadboard, or even a veroboard, for more permanence once you have confidence in correctness. This will definitely save time correcting errors and help keep the magic smoke safely contained within those mysterious black rectangles.

As it stands, the tools are limited to a few select ICs, which, much to this scribe’s disappointment, did not include the venerable 555 timer; however, it would be possible to work around that with some imagination at the schematic level. The ability to drop in and document power supply, function generator, and oscilloscope probing points is nice, enabling one to close the loop on documenting a layout to make it truly transferable to physical reality.

We cover electronics prototyping with breadboards a lot because they’re accessible. Here’s a super simple computer on a breadboard. We also like seeing them integrated as tools, like here. Finally, why stick with the tired old common breadboard shapes when you could make your own?

With MCUs becoming increasingly more powerful it was only a matter of time before they would enable some more serious audio-processing tasks. [Danilo Gabriel]’s ESP32Synth library is a good example here, which provides an ESP-IDF based 80+ voice mixing and synthesis engine. If you ever wanted to create a pretty impressive audio synthesizer, then all you really need to get started is an ESP32, ESP32-S3 or similar dual-core Espressif MCU that has the requisite processing power.

Audio output goes via I2S, requiring only a cheap I2S DAC like the UDA1334A or PCM5102 to be connected, unless you really want to use the internal DAC. With this wired up you get 80 voices by default, with up to 350 voices demonstrated before the hardware cannot keep up any more. You can stream multiple WAV files from an SD card for samples along with the typical oscillators like sinewave, triangle, sawtooth and pulse, as well as noise, wavetables and more.

In order to make this work in real-time a number of optimizations had to be performed, such as the removal of slow floating-point and division operations in the audio path. The audio rendering task is naturally pinned to a single core, leaving a single core for application code to use for remaining tasks. While the code is provided as an Arduino project, it uses ESP-IDF so it can likely be used for a regular ESP-IDF project as well without too much fuss.

One of the problems facing any solar power installation comes in storing enough power for high-intensity operations such as cooking. The high-tech and expensive way involves battery banks and inverters, but [Solar Genius] is taking a more direct route by skipping the energy storage entirely.

A pair of parabolic antennas are pressed into service as mirrors, catching and focusing the sun’s energy onto a cooking pot. Of course, solar cookers like this are nothing new, so what makes this one different is the in-depth analysis of its performance. This thing can cook!

One antenna is covered in square mirrors while the other is covered in sticky chrome-effect mirror sheeting. They’re described as sun tracking, but since we don’t see any mechanism we’re guessing the tracking is done by hand. The experiment takes place in Pakistan, so there’s a plentiful supply of sunlight that those of us in more northern climes can only dream of.

This hack is part of our 2026 Green Powered Challenge. You’ve just got time to get your own entry in, so get a move on!

Keeping plants alive is easy if you’re diligent and never forget to check on your green friends. However, a little electronic help never hurts. To that end, [Narrow Studios] built a simple solar powered monitor to assist in plant maintenance, and it mostly does the job.

An ESP32-C3 development board serves as the brains of the operation. It’s set up with a capacitive soil moisture sensor, a great choice because they tend to last longer than other types. Power is courtesy of a small lithium-polymer battery and a solar panel, which keeps everything running off the juice from interior lighting alone. SK6812 addressable LEDs are used to show current soil moisture status. To avoid excessively draining the batteries with the limited power available, a HCSR505 PIR motion sensor is used to only light the status LEDs if the device detects someone in the vicinity.

There were some issues in the build. The voltage regulator doesn’t supply enough current to enable the ESP32 to jump on WiFi, so soil dryness indication is via LED only. The solar setup is a little weak, too. Still, the project was a great learning experience and with a few mods, would be even more capable.

We’ve featured some great plant monitors over the years, like this Hackaday Prize entry from 2023.