Better Air Quality Sensing With CO2

Measuring air quality, as anyone who has tried to tackle this problem can attest, is not as straightforward as it might seem. Even once the nebulous term “quality” is defined, most sensors use something as a proxy for overall air health. One common method is to use volatile organic compounds (VOCs) as this proxy but as [Larry Bank] found out, using these inside a home with a functional kitchen leads to a lot of inaccurate readings. In the search for a more reliable sensor, he built this project which uses CO2 to help gauge air quality.

Most of the reason that CO2 sensors aren’t used as air quality sensors is cost. They are much more expensive than VOC sensors, but [Larry] recently found one that was more affordable and decided to build this project around it. The prototype used an Arduino communicating over I2C to the sensor and an OLED screen, which he eventually put in a 3D printed case to carry around to sample CO2 concentration in various real-world locations. The final project uses a clever way of interfacing with the e-paper display that we featured earlier.

While CO2 concentration doesn’t tell the full story of air quality in a specific place, it does play a major role. [Larry] found concentrations as high as 3000 ppm in his home, which can cause a drop in cognitive function. He’s made some lifestyle changes as a result which he reports has had a beneficial impact. For human-occupied indoor spaces, CO2 can easily be the main contributor to poor air quality, and we’ve seen at least one other project to address this concern directly.

Ceiling Fan Adds CO2 Sensor

Ceiling fans seem to be an oft-misunderstood or overlooked household appliance. As such, they seem to have missed a lot of the IoT wave. Sure, you can get smart controllers for them to plug into your home automation system of choice, but these mostly rely on temperature sensors, simple timers, or voice commands. There’s a lot more to a ceiling fan than maintaining a comfortable temperature, as [EJ] demonstrates with this smarter ceiling fan build.

A big part of the job of a ceiling fan is to improve air circulation, which can help a room from feeling “stuffy”. This feeling is usually caused by excess CO2 as a result of respiration in an area where the air is not moving enough to exhaust this gas. Not only does [EJ]’s controller make use of a temperature monitor for controlling the fan automatically, but there is also a CO2 sensor integrated to improve this aspect of air quality when needed.

The entire build is based on a Raspberry Pi Zero, and nothing needed to be changed about the ceiling fan itself for this added functionality because it already included a radio-based remote control. With some monitoring of the signals produced by the remote, the Raspberry Pi was programmed to mimic these commands when the surrounding sensors captured a condition where [EJ] would want the fan on. There’s also a manual control button as well, so the fan control is not entirely in the hands of the computer.

For a little more detailed information about this build, there’s a separate project page which details a lot of the information about the RF waveform capturing and recreation. And, if you want to take your fan to the next level, take a look at this one which focuses on building a smartphone app to control the fan instead.

Trombone Controls Virtual Trombone

Guitar Hero was a cultural phenomenon a little over a decade ago, and showed that there was a real fun time to be had playing a virtual instrument on a controller. There are several other similar games available now for different instruments, including one called Trombone Champ that [Hung Truong] is a fan of which replaces the traditional guitar with a trombone. The sliding action of a trombone is significantly different than the frets of a guitar, making it a unique challenge in a video game. But an extra challenge is building a controller for the game that works by playing a real trombone.

Unlike a guitar which can easily map finger positions to buttons, mapping a more analog instrument like a trombone with its continuous slide to a digital space is a little harder. The approach here was to use an ESP32 and program it to send mouse inputs to a computer. First, an air pressure sensor was added to the bell of the trombone, so that when air is passing through it a mouse click is registered, which tells the computer that a note is currently being played. Second, a mouse position is generated by the position of the slide by using a time-of-flight sensor, also mounted to the bell. The ESP32 sends these mouse signals to the computer which are then used as inputs for the game.

While [Hung Truong] found that his sensors were not of the highest quality, he did find the latency of the control interface, and the control interface itself, to be relatively successful. With some tuning of the sensors he figures that this could be a much more effective device than the current prototype. If you’re wondering if the guitar hero equivalent exists or not, take a look at this classic hack from ’09.

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A Simple Web Configured BLE To GPIO Bridge

[Daniel Dakhno] kept ending up in a situation where the ability to read the status of, or control a few digital IO pins with minimal effort, would be terribly useful. Not wanting to keep compiling code, for such simple needs, they instead used a nRF51-based module as a physical interface and produced a general purpose firmware that could be configured with a simple web interface. The NRF51-IO-module was born, whose job is to pair with whatever device you have in front of you, provided it supports BLE, and give direct access to those IO pins.

Rather than acting as a rather slow logic analyser, the firmware is intended for mostly static configurations. The web application sends a configuration packet over to the nRF51 board, which then programs it into FLASH and restarts, reading the updated configuration and applying it to the IO pins. These outputs then persist as long as there is power. The read-side of the equation can also be performed via the web page, but we didn’t have a chance to verify that. The code implements the Bluetooth automation IO service as well as the binary sensor service so if you have access to applications that talk these services, then you should be able to fire it up and go with it, although we’ve not personally tested this due to lack of an nRF51 board. We noticed that the Home Assistant automation platform supports the BT binary sensor, which might be a big help for some people with a need for some wireless control and sensing.

If you need a practical example of a use for remote sensing, here’s a physical mailbox status monitor, using the nRF51. Whilst we’re thinking of Bluetooth and sensors, here’s a custom firmware for some super cheap environment sensors that frees them from vendor lock-in.

Header image: Ubahnverleih, CC0.

2022 Hackaday Prize: Plant Monitoring System Grows To Include LoRa

Change on industrial scales is slow, but if you’re operating your own small farm or simply working in a home garden there are some excellent ways to use water more effectively. The latest tool from [YJ] makes it possible to use much less water while still keeping plant yields high.

This is an improvement on a previous project which automates watering and lighting of a small area or single pot. This latest creation, called FLORA, includes a LoRa module for communication up to 3 kilometers, and the ESP32 on board also handles monitoring of soil moisture, humidity and other sensors. It also includes a pump driver for managing irrigation systems so that smart decisions can be made about when to water. Using this device, the water usage when testing was reduced by around 30% compared to a typical timed irrigation system.

Using a smart system like this is effective for basically any supply of water, but for those who get water from something like an off-grid rainwater system or an expensive water utility, the gains are immediate. If you aren’t already growing your own food to take advantage of tools like this, take a look at this primer to get you started.

Presence-Detecting Cushion Keeps You From Sitting Your Life Away

They say that sitting is the new smoking. They’re wrong — smoking is much, much worse, for you than sitting, and smoking only while standing or while jogging around the block in no way to justify the habit. But they’re also not wrong that humans weren’t made for extended periods parked on their posteriors, but we do it anyway, to the detriment of our heart health, posture, and general well-being. So something like this butt-detecting stand-up reminder could make a big difference to your health.

While like many of us, [Dave Bennett] has a wearable that prompts him to get up and move around after detecting 30 minutes of sitting, he found that it’s too easy to dismiss the alarm and just go right on sitting. Feeling like he needed a little more encouragement to get up and go, he built a presence detector completely from scratch. His sensor is a sheet of static-protective Velostat foam wrapped in conductive tape; when compressed, the resistance across the pad drops, making it easy to detect with a simple comparator circuit.

We admit to getting excited when we first saw the alarm circuit; a quick glance at the schematic seemed like it was based on a 555, which it totally could be. But no, [Dave]’s design goals include protection against spoofing the alarm with a quick “cheek sneak,” which was most easily implemented in code. So that 8-pin device in the circuit is an ATtiny85, which sounds the alarm after 30 minutes and requires him to stay off his butt for a full minute before resetting. The video below hits the high points of design and shows it in use.

Annoying? Yes, but that’s the point. Of course a standing desk would do the same thing, but that’s not going to work for everyone, so this is a nice alternative.

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Scavenging CDs For Flexible Parts

CDs are becoming largely obsolete now, thanks to the speed of the internet and the reliability and low costs of other storage media. To help keep all of this plastic out of the landfills, many have been attempting to find uses for these old discs. One of the more intriguing methods of reprurposing CDs was recently published in Nature, which details a process to harvest and produce flexible biosensors from them.

The process involves exposing the CD to acetone for 90 seconds to loosen the material, then transferring the reflective layer to a plastic tape. From there, various cutting tools can be used to create the correct pattern for the substrate of the biosensor. This has been shown to be a much more cost-effective method to produce this type of material when compared to modern production methods, and can also be performed with readily available parts and supplies as well.

The only downside to this method is that it was only tested out on CDs which used gold as the conducting layer. The much more common aluminum discs were not tested, but it could be possible with some additional research. So, if you have a bunch of CD-Rs laying around, you’re going to need to find something else to do with those instead.

Thanks to [shinwachi] for the tip!