Air Extractor Automatically Gives AC A Boost

Portable air conditioning units are a great way to cool off a space during the hot summer months, but they require some place to blow the heat they’ve removed from your room. [VincentMakes] got a portable AC unit for his home, but he found that the place he wanted to put it was too far from the only window he could use to dump the hot air. Having too long of a duct on the hot air exhaust increases the back pressure on the fan which could cause it to prematurely fail, so [Vincent] used an extractor fan to automatically give is AC unit’s exhaust a boost on its way to the window.

Because his AC can operate at low, medium, and high speeds, he chose an extractor fan that also supported multiple speeds and took care to match the airflow of the AC and extractor fan to avoid putting too much strain on either fan. He designed a system to automatically set the speed of the boosting fan to match that of the AC using a Hall effect current sensor to measure the AC unit’s power draw and an Arduino Nano for control. A custom PCB interfaces the Nano to the Hall Sensor and control relays, and we have to applaud [Vincent] for keeping the +5V DC and 230V AC far, far away from each other. In addition to this fine electronics work, [Vincent] also built an enclosure for the fan controller that allows the fan to be mounted on top at an angle, which helps avoid having hard bends in the exhaust duct.

If this has you thinking about smart air conditioners to keep cool this summer, check out this ESP8266-powered smart AC system, or this Raspberry Pi-based system that controls both AC and blinds!

Arduino Variometer In A Mint Tin

While humans have done a pretty good job of figuring out how to fly with various mechanical contrivances, the fact remains that our natural senses aren’t really well suited to being off the ground. For example, unless you have a visual reference point, determining which way is up is quite a bit harder than you might think. Which is why pilots rely on instruments such as the variometer, that determines the current rate of climb and descent, to guide them when their eyes can’t be trusted.

It’s also a very handy thing to have when paragliding, which is why [mircemk] decided to build a hand-held version using the Arduino Nano and a BMP180 pressure sensor. Since you don’t want to be staring at a little screen in mid-air, the device conveys changes in altitude with audio tones. A rising tone means you’re moving upwards, while a lower tone indicates downward travel. In the video below, you can see that it only takes a meter or two of vertical movement before the device picks up on the change.

Looking for a simple yet rugged enclosure for the device, [mircemk] found a metal mint tin that would hold the microcontroller, sensor, buzzer, and the 9 V battery that powers it all. We know what you’re thinking, but don’t worry; holes have been popped in the sides to make sure there’s no pressure difference inside the tin. There’s plenty of room to replace the alkaline battery with a rechargeable pack and associated charge controller, but we imagine there’s a certain security in tossing in a fresh new primary cell before slipping the surly bonds of Earth.

If you’re in interested DIY instrumentation for a glider or other aircraft that actually has a proper cockpit, this sunlight readable flight computer made from a Kobo e-reader would be a great start.

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Simple Probe Sniffs Out EMI

Unable to account for the strange glitches he was seeing on his DIY CNC router, [Daniël Van Den Berg]  wondered if his electronics might be suffering from some form of electromagnetic interference (EMI). So he did what any good hacker would do, and rummaged through the parts bin to build an impromptu EMI detector.

[Daniël] is quick to point out that he’s not an electrical engineer, and makes no guarantees about the accuracy of his tossed together gadget. But it does seem to work well enough in his testing that he’s able to identify particularly “noisy” electronic components, so it’s probably worth putting one together just to hear what your hardware is pumping into the environment.

The hardware here is very simple, [Daniël] just attached a coil of solid copper wire to one of the analog pins on an Arduino Nano with a resistor, and hung a speaker off of one of the digital pins. From there, it just took a few lines of code to read the voltage in the coil and convert that into a tone for the speaker. The basic idea is that a strong alternating magnetic field will set up voltage fluctuations in the coil large enough for the Arduino’s ADC to read.

If you’re looking for a bit more insight into what kind of interference your electronic creations might be putting out, [Alex Whittimore] gave a fantastic presentation during the 2020 Hackaday Remoticon about performing RF debugging using a cheap RTL-SDR dongle.

Automated Watering Machine Has What Plants Crave: Fertilizer

We’ve seen countless automated plant care systems over the years, but for some reason they almost never involve the secret sauce of gardening — fertilizer. But [xythobuz] knows what’s up. When they moved into their new flat by themselves, it was time to spread out and start growing some plants on the balcony. Before long, the garden was big enough to warrant an automated system for watering and fertilizing.

This clever DIY system is based around a 5L gravity-fed water tank with solenoid control and three [jugs] of liquid fertilizer that is added to the water via peristaltic pump. Don’t worry, the water tank has float switches, and [xythobuz] is there to switch it off manually every time so it doesn’t flood the flat.

On the UI side, an Arduino Nano clone is running the show, providing the LCD output and handling the keypad input. The machine itself is controlled with an ESP32 and a pair of four-channel relay boards that control the inlet valve, the four outlet valves, and the three peristaltic pumps that squirt out the fertilizer. The ESP also serves up a web interface that mimics the control panel and adds in the debug logs. These two boards communicate using I²C over DB-9, because that’s probably what [xythobuz] had lying around. Check out the demo video after the break, and then go check on your own plants. They miss you!

Don’t want to buy just any old peristaltic pumps? Maybe you could print your own.

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Eyecam Is Watching You In Between Blinks

We will be the first to admit that it’s often hard to be productive while working from home, especially if no one’s ever really looking over your shoulder. Well, here is one creepy way to feel as though someone is keeping an eye on you, if that’s what gets you to straighten up and fly right. The Eyecam research project by [Marc Teyssier] et. al. is a realistic, motorized eyeball that includes a camera and hangs out on top of your computer monitor. It aims to spark conversation about the sensors that are all around us already in various cold and clinical forms. It’s an open source project with a paper and a repo and a how-to video in the works.

The eyebrow-raising design pulls no punches in the uncanny department: the eye behaves as you’d expect (if you could have expected this) — it blinks, looks around, and can even waggle its brow. The eyeball, brow, and eyelids are actuated by a total of six servos that are controlled by an Arduino Nano.

Inside the eyeball is a Raspberry Pi camera connected to a Raspi Zero for the web cam portion of this intriguing horror show. Keep an eye out after the break for the Eyecam infomercial.

Creepy or fascinating, it succeeds in making people think about the vast amount of sensors around us now, and what the future of them could look like. Would mimicking eye contact be an improvement over the standard black and gray oblong eye? Perhaps a pair of eyes would be less unsettling, we’re not really sure. But we are left to wonder what’s next, a microphone that looks like an ear? Probably. Will it have hair sprouting from it? Perhaps.

Yeah, it’s true; two eyes are more on the mesmerizing side, but still creepy, especially when they follow you around the room and can shoot frickin’ laser beams.

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Nixie Shot Timer Adds Useful Elegance To Espresso Machine

Once you’ve ground the beans and tamped the grounds just so, pulling the perfect shot of espresso comes down to timing. Ideally, the extraction should last 20-30 seconds, from the first dark drips to the tan and tiger-striped crema on top that gives the espresso a full aftertaste.

[Marco] has a beautiful espresso machine that was only missing one thing: an equally beautiful shot timer with a Nixie tube display. Instead of messing with the wiring, [Marco] took the non-invasive approach and is using a DIY coil to detect the magnetic field of the espresso machine’s pump and start a shot timer.

An LM358-based op-amp magnifies the current induced by the machine and feeds it to an Arduino Nano, which does FFT calculations. [Marco] found a high-voltage interface driver to switch 170 V to the Nixies instead of using two handfuls of transistors. Grab yourself a flat white and check it out after the break.

The last Nixies may have been mass-produced in the 1980s, but never fear — Dalibor Farny is out there keeping the dream alive and making new Nixies.

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Negative Reinforcement: Drill Bits Edition

In theory, it’s fun to have a lot of toys tools around, but the sad reality is that it’s only as fun as the organization level applied. Take it from someone who finds organization itself thrilling: it really doesn’t matter how many bits and bobs you have, as long as there’s a place for everything and you put away your toys at the end of the day.

[Cranktown City] is always leaving drill bits lying around instead of putting them back in their bit set boxes. Since he responds well to yelling, he decided to build an intelligent drill bit storage system that berates him if he takes one out and doesn’t put it back within ten minutes.

But [Cranktown City] did much more than that. The system is housed in a really nice DIY stand that supports his new milling and drilling machine and has space to hold a certain type of ubiquitous red tool box beneath the drill bits drawer.

All the bits now sit in a 3D-printed index that fits the width of the drawer. [Cranktown City] tried to use daisy-chained pairs of screws as contacts behind each bit that could tell whether the bit was home or not, but too much resistance interfered with the signal. He ended up using a tiny limit switch behind each bit instead. If any bit is removed, the input signal from the index goes low, and this triggers the Arduino Nano to do two things: it lights up a strip of red LEDs behind the beautiful cut out letters on the drawer’s lip, and it starts counting upward. Every ten minutes that one or more bits are missing, the drawer complains and issues ad hominem attacks. Check out the demo and build video after the break, but not until you put your tools away. (Have you learned nothing?)

Okay, so how do you deal with thousands of jumbled drill bits? Calipers and a Python script oughta do it.

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