Building (And Testing) A DIY Air Purifier

January 29, 2020 by Tom Nardi 64 Comments

Whether it’s the usual pollution of the city, or the fact that your corner of the globe happens to be on fire currently, poor air quality is a part of daily life for many people. One way of combating this issue is with a high quality HEPA filter in your home, but unfortunately that’s not something that everyone can afford to even has access to.

Which is why [Adam Kelly] decided to design this DIY HEPA air purifier that can be built for less than $100. That might still sound like a lot of money, but compared to the $500 sticker price he was seeing for the models recommended by health officials, it’s certainly a step in the right direction. Of course, it’s only a deal if it actually works, so a big part of the project has also been verifying the design’s ability to filter particles out of the air in a timely manner.

To build his purifier, [Adam] found a HEPA H13 rated replacement filter that was cheap and readily available, and started designing a low-cost way to pulling air through it. He eventually went with a 120 mm computer case fan coupled with a step-up converter that can produce 12 V from a standard USB port. Then he just needed to design a 3D printed “lid” which would position the fan so it draws air through the center of the filter.

In terms of testing, [Adam] wasn’t worried about the purifier’s ability to actually filter out smoke particles; unless the manufacturer lied about the capabilities of the filter itself, that part is a given. But he was curious about how effective the fan would be in terms of circulating air through a room.

By installing a pitot tube from one of his drones into the lid of the purifier, he determined the airflow in the center of the filter to be approximately 160 CFM. By his calculations, that means it should be able to circulate all the air in his 25 cubic meter office around 10 times per hour. That’s a promising start, but [Adam] says he’d still be interested in a more detailed analysis of the design’s performance by anyone who might have the equipment to do so.

As he lives in Australia, this project is more than just a passing fancy for [Adam]. He only has to look out the window to see that the air he’s breathing is filled with smoke from the raging bushfires. They say that necessity is the mother of invention, and breathable air is pretty high up on the list of human necessities. Our hat’s off to anyone who sees their fellow citizens suffering and tries to use their skills to come up with a solution.

An Eight-Day Home Automation Hackathon Is Inspiration For Getting More Projects Done

January 24, 2020 by Mike Szczys 11 Comments

There’s nothing quite like a deadline to cut through extras and get right at the heart of the problem. Maybe we should all follow Interpreet’s example and stop thinking about automating our homes and just make it in an eight-day hackathon. His talk at the 2019 Hackaday Superconference covers the zero-to-deployment home automation build he finished in the eight days leading up to his move from one continent to another.

Hackaday’s very own Inderpreet Singh found himself pulling up roots and moving from his home in India to teach at Centennial College in Toronto, Canada. He needed a way to keep an eye on his home from afar and the name of the game is IoT. When the only choice is “whatever works right now”, you can learn a lot about simple solutions.

He chose familiar hardware to work with, with the ESP8266 making up the bulk of the nodes and a Raspberry Pi as as a central hub for the setup. He chose to communicate between all the nodes on his system using WiFi because the hardware is robust and available. With security in mind, he keeps the automation system separate from the daily use WiFi system by grabbing an extra access point to serve as the automation network. The Raspberry Pi serves as a router of sorts; its Ethernet port is connected to the IoT device’s AP, while the onboard WiFi is used to connect to the home’s main AP for a connection to the wider Internet.

Software for the system is built on a REST API served by a Python Flask app. Many would advocate for using MQTT but Inderpreet’s testing with that protocol came up short as the broker he intended to use was no longer available. One of the interesting parts of his system design is that all nodes will check in at regular intervals; this allows them to inquire about actions they need to take, but it also allows the system to detect a malfunctioning node immediately. I’ve seen a similar trick used by Elliot Williams where he assigns a “ping” topic to all MQTT devices that causes them to report in with their IP address. Having a system to query and ensure the health of every node is a big tip to take away from this talk.

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BinDayCator Lets You Know When To Take Out The Trash

January 23, 2020 by Lewin Day 39 Comments

Municipal waste pickup is a wonderful luxury. Typically once a week, large trucks come by and pick up bins of garbage from your residence. All you have to do is remember to put them out! In a uniquely human way, this is very hard to do. Enter the BinDayCator.

The project consists of a 3D printed model of a typical council wheelie-bin. Printed in white filament, the bin is translucent enough to glow when lit by powerful WS2812B LEDs. Having four LEDs both helps fill the entire model with an even light, as well as allows the bin to display multiple colors in different segments. This means that if it’s green bin day, the bin glows green. If it’s the day for the red and blue bins, the indicator will light up segments in red and blue.

Unfortunately there’s no global standard that councils use to serve up bin day data over the Internet, so configuration isn’t as simple as pointing the BinDayCator at your local waste authority’s website. Instead, some Node-RED code is used to scrape the council website once a day and tell the ESP8266 controlling the BinDayCator which bins are due to be placed on the roadside. A later revision has a custom calendar UI that can allow for manual configuration of the relevant days.

The BinDayCator is a cute device, and one that would likely be commercially successful if there were a simple and easy way to configure the necessary data feed. We’d love one by our front door so we didn’t miss another collection day. Visual indicators are always useful, even if its just for checking the mail. Video after the break.

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A Battery Sipping Cellular Mailbox Notifier

January 22, 2020 by Tom Nardi 16 Comments

Like many of us, [Zak Kemble] has an indeterminate number of tiny packages coming his way from all over the globe at any given time. Unfortunately, the somewhat unpredictable nature of the postal service where he lives meant he found himself making a lot of wasted trips out to the mailbox to see if any overseas treasures had arrived for him. To solve the problem, he decided to build an Internet-connected mailbox notification system that could work within some fairly specific parameters.

For one thing, the mailbox is too distant to connect directly to it over WiFi. [Zak] mentions that 433 MHz might have been an option, but he decided to skip that entirely and just connect it to the cellular network with an A9G GPRS/GSM module from A.I. Thinker. This device actually has its own SDK that allows you to create a custom firmware for it, but unfortunately the high energy consumption of the radio meant it would chew through batteries too quickly unless it had a little extra help.

Not wanting to have to change the batteries every couple months, [Zak] added a ATtiny402 to handle the notifier’s power management needs. By using a P-MOSFET to completely cut power to the A9G, the notifier can save an incredible amount of energy by only activating the cellular connection once it actually needs to send a notification; which in this case takes the form of an HTTP request that eventually works its way to a Telegram group chat.

To cut a long story short, testing seems to indicate that the notifier can fire off approximately 800 requests before needing its 10440 lithium battery recharged. Given how often [Zak] usually receives mail, he says that should last him around five years.

The A9G module, the ATtiny402, a BME280 environmental sensor (because, why not?), the battery, and all the ancillary support hardware are on a very professional looking PCB. That goes into a relatively rugged enclosure that’s designed to keep the electronics from shorting out on the mailbox’s metal case as well as keeping any particularly weighty parcels from crushing it.

If you’ve got the freedom so mount whatever you want outside, then you can certainly build a more technically impressive mailbox. But considering the limitations [Zak] had to work around, we think he did an excellent job.

Reverse Engineering Yokis Home Automation Devices

January 21, 2020 by Tom Nardi 12 Comments

These days, it’s hard to keep track of all the companies that are trying to break into the home automation market. Whether they’re rebrands of somebody else’s product or completely new creations, it seems like every company has at least a few “smart” gadgets for you to choose from. We hadn’t heard of the Yokis devices that [Nicolas Maupu] has been working on before today, but thanks to his efforts to reverse engineer their protocol, we think they might become more popular with the hacking crowd.

Even if you don’t have a Yokis MTV500ER dimmer or MTR2000ER switch of your own, we think the detailed account of how [Nicolas] figured out how to talk to these devices is worth a read. His first step was to connect his oscilloscope directly to the SPI lines on the remote to see what it was sending out. With an idea of what he was looking for, he then used an nRF24L01+ radio connected to an ESP8266 to pull packets out of the air so he could analyze their structure. This might seem like a very specialized process, but in reality most of the techniques demonstrated could be applicable for any unknown communications protocol of which you’ve got a hex dump.

On the other hand, if you do have some of these devices (or plan to get them), then the software [Nicolas] has put together looks very compelling. Essentially it’s an interactive firmware for the ESP8266 that allows it to serve as a bridge between the proprietary Yokis wireless protocol and a standard MQTT home automation system. When the microcontroller is connected to the computer you get a basic terminal interface that allows you to scan and pair for devices as well as toggle them on and off.

This bridge could be used to allow controlling your Yokis hardware with a custom handheld remote, or you could follow the example of our very own [Mike Szczys], and pull everything together with a bit of Node-RED.

A Simple Auger Pet Feeder

January 17, 2020 by Lewin Day 14 Comments

Pet feeders are a popular maker project. One can speculate that this shows the great self-confidence common to the maker set, who are willing to trust their own work to keep their animal companions alive for many days at a a time. [Darren Tarbard] is one such maker, who put together this simple auger build.

The project consists of a hopper for dry pet food, into which a screw auger is inserted. Both parts are 3D printed, making them easy to produce at home for the average maker. The build was designed specifically around the parts [Darren] had to hand, namely a 28BYJ-48 stepper motor, which is charged with turning the auger. Running the show is an Arduino, which can be run with whatever suitable timing code is necessary to feed the particular pet in question. There’s also a remixed version that adds a larger food storage dish on top for longer periods of unattended operation, created by [szuchid].

It’s a basic build, but one that would be readily achievable by most makers with little more than some junkbox components and a roll of filament. Of course, if your pet prefers wet food, you might need a different design. Video after the break.

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Datacenter UPS Heads Home For Off-Grid Power Solution

January 4, 2020 by Jenny List 63 Comments

The news sites seem never to be without stories of Elon Musk and his latest ventures, be they rapid transit tube tubes in partial vacuum, space flight, or even personal not-a-flamethrowers. Famous for electric vehicles, Musks’s Tesla also has a line of solar products and offers the Powerwall home battery power system. These are tantalizing to anyone with solar panels, but the price tag for one isn’t exactly a dream.

[Nathann]’s budget couldn’t stretch to a Powerwall, but he did have access to a hefty ex-datacentre uninterruptible power supply (UPS) and a large quantity of lead-acid cells. From this he built his own off-the-grid power in the cellar of the home. It’s not as elegant as a Powerwall, but it can power the house on moderate usage, so he claims, for up to ten days.

On one level the installation is more of a wiring job than one of high technology, but the logistics of dealing with nearly 100 lead-acid cells are quite taxing. The UPS takes four battery packs, each clocking in at 288 V. The cells are joined with copper straps, and the voltage and current involved is not for the faint-hearted. An accidental short vaporized a screw and a battery terminal; if this were our house we’d put fuses in the middle of the battery packs.

The batteries are stored on wooden pallets atop brick pillars in case the cellar floods. The basement installation now is ready for the addition of solar and wind-based off-grid sources. Maybe your battery power solution will be less hair-raising, but it’s unlikely to be cheaper. Meanwhile this isn’t the first such project we’ve seen, though others usually go for 18650 Li-Ion cells, the use of lead acid remains a viable and economical solution.