Supercapacitors In A Servo: The “Forever” Flashlight

The principle is well understood: use a motor in reverse and you get a generator. Using this bit of knowledge back in 2001 is what kick-started [Ted Yapo]’s Hackaday Prize entry. At the time, [Ted] was searching for a small flashlight for astronomy, but didn’t like dealing with dead batteries. He quickly cobbled together a makeshift solution out of some supercapacitors and a servo-as-a-generator, hacked for continuous rotation.

A testament to the supercapacitors, 17 years later it’s still going strong – leading [Ted] to document the project and also improve it. The original circuit was as simple as a servo, protection diode, some supercapacitors, and a LED with accompanying resistor; but now greater things are afoot.

A DC-DC boost converter enables constant power through the LED, regardless of the capacitor voltage. This is achieved by connecting the feedback pin of an MCP1624 switcher to an INA199 current-shunt monitor. The MCP1624 kicks in at 0.65V and stays active down to 0.35V. This is all possible due to the supercapacitors, which happily keep increasing current as voltage drops – all the way to 0.35V. Batteries are less ideal in this situation, as their internal resistance increases as voltage drops, as well as increasing with age.

When testing the new design, [Ted] found that the gears on his servos kept stripping when he was using them to charge capacitors. Though at first he attributed it to the fact that the gears were plastic, he realized that his original prototype from 2001 had been plastic as well. Eventually, he discovered the cause: modern supercapacitors are too good! The ones he’d been using in 2001 were significantly less advanced and had a much higher ESR, limiting the charging current. The only solution is to use metal gear servos

Want to read more about boost converter design? We have the pros and cons of microcontrollers for boost converters, or this neat Nixie driver for USB power.

Tiny $25 Spectrometer Aims to Identify Materials with Ease

Reflectance spectrometers work on a simple principle: different things reflect different wavelengths in different amounts, and because similar materials do this similarly, the measurements can be used as a kind of fingerprint or signature. By measuring how much of which wavelengths get absorbed or reflected by a thing and comparing to other signatures, it’s possible to identify what that thing is made of. This process depends heavily on how accurately measurements can be made, so the sensors are an important part.

[Kris Winer] aims to make this happen with the Compact, $25 Spectrometer entry for The 2018 Hackaday Prize. The project takes advantage of smaller and smarter spectral sensors to fit the essential bits onto a PCB that’s less than an inch square. If the sensors do the job as expected then that’s a big part of the functionality of a reflectance spectrometer contained in a PCB less than an inch square and under $25; definitely a feat we’re happy to see.

RCA TV Gets New Life As Interactive Atltvhead

TVs are usually something you sit and passively watch. Not so for [Nate Damen’s] interactive, wearable TV head project, aka Atltvhead. If you’re walking around Atlanta, Georgia and you see him walking around with a TV where his head should be, introduce yourself! Or sign into Twitch chat and take control of what’s being displayed on the LEDs which he’s attached to the screen. Besides being wearable technology, it’s also meant to be an interactive art piece.

For this, his third version, the TV is a 1960’s RCA Victor Portable Television. You can see some of the TVs he found for previous versions on his hackaday.io page. They’re all truly vintage. He gutted this latest one and attached WS2812 LED strips in a serpentine pattern inside the screen. The LEDs are controlled by his code and the FastLED library running on an ESP8266. Power comes from four NiMH AA-format batteries, giving him 5 V, which he regulates down to 3.3 V. His phone serves as a WiFi hotspot.

[Nate] limits the commands so that only positive things can be displayed, a heart for example. Or you can tweak what’s being displayed by changing the brightness or make the LEDs twinkle. Judging by the crowds we see him attracting in the first video below, we’d say his project was a huge success. In the second video, Nate does a code walkthrough and talks about some of his design decisions.

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Watch the Honeycomb Clock Gently Track Time

We love clocks here at Hackaday, and so does [John Whittington]. Last year he created this hexagonal honey clock (or “Honock”) by combining some RGB LEDs with a laser-cut frame to create a smooth time display that uses color and placement to display time with a simple and attractive system.

The outer ring of twelve hexagons is essentially the hour hand, similar to analog clock faces: twelve is up, three is directly to the right, six is straight down, and nine is to the left. The inner ring represents ten minutes per hex. Each time the inner ring fills, the next hex (hour) on the outer ring lights up. The whole display is flooded with a minute-long rainbow at noon and midnight. Watch it in action in the video, embedded below.

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Animated Bluetooth Bike Turn Signals

Tired of risking his life every time he had to signal a turn using his hands while riding his bicycle in rainy Vancouver, [Simon Wong] decided he needed something a bit higher tech. But rather than buy something off the shelf, he decided to make it into his first serious Arduino project. Given the final results and the laundry list of features, we’d say he really knocked this one out of the park. If this is him getting started, we’re very keen to see where he goes from here.

So what makes these turn signals so special? Well for one, he wanted to make it so nobody would try to steal his setup. He wanted the main signal to be easily removable so he could take it inside, and the controls to be so well-integrated into the bike that they wouldn’t be obvious. In the end he managed to stuff a battery pack, Arduino Nano, and an HC-05 module inside the handlebars; with just a switch protruding from the very end to hint that everything wasn’t stock.

On the other side, a ATMEGA328P microcontroller along with another HC-05 drives two 8×8 LED matrices with MAX7219 controllers. Everything is powered by a 18650 lithium-ion battery with a 134N3P module to bring it up to 5 VDC. To make the device easily removable, as well as keep the elements out, all the hardware is enclosed in a commercial waterproof case. As a final touch, [Simon] added a Qi wireless charging receiver to the mix so he could just pull the signal off and drop it on a charging pad without needing to open it up.

It’s been some time since we’ve seen a bike turn signal build, so it’s nice to see one done with a bit more modern hardware. But the real question: will he be donning a lighted helmet for added safety?

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Investigating the Tiny Salvaged UPS from a Lightbulb

Recently I had the opportunity to do a teardown of a battery-backed LED bulb, and found some interesting details on how the device operated. Essentially, the bulb contained a low voltage DC uninterruptible power supply that would automatically switch between AC power and internal battery as needed. The implications of this seemed pretty exciting. For around $12 at big box retailers, this little bulb could be a cheap and convenient solution for providing fault tolerant power to microcontrollers and other low-power devices.

The teardown was a runaway success, with quite a bit of discussion of the UPS idea specifically. Some people hated it, others loved it. But as we’ve come to expect from Hackaday readers, the comments from both sides of the aisle contained keen observations and invaluable real-world experience. From the safety of the device to the accuracy of the manufacturer’s claims, it seems like every element of the product was addressed.

I had ended the teardown with a promise that I’d continue experimenting with the tiny salvaged UPS, but even if I hadn’t, with so much feedback it seemed revisiting the subject was all but a necessity. It this little UPS really viable? Is it too dangerous to safely implement in your project? Will the thing just blow up?

So with your comments as a guide, and free of the somewhat restrictive teardown format, I set out to conduct a more thorough investigation of this little circuit that caused so much debate last month. It’s not all good news, but it’s not in the trash either. Not yet, anyway.

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It’s Not Morning Until Green o’clock

[JohnathonT] has a two-year-old who can’t reliably tell time just yet. Every morning, he gets up before the rooster crows and barges into his parents’ room, ready to face the day.

In an effort to catch a few more Zs, [JohnathonT] built a simple but sanity-saving clock that tells time in a visual, kid-friendly way. Sure, this is a simple build. But if a toddler is part of your reality, who has time to make one from logic gates? The hardware is what you’d expect to see: Arduino Nano, a DS1307 RTC, plus the LEDs and resistors. We think an RGB LED would be a nice way to mix up the standard stoplight hues a bit.

At a glance, little Mr. Rise and Shine can see if it’s time to spread cheer, or if he has to stay in his room and play a bit longer. At 6:00AM, the light powers on and glows red. At 6:50, it turns yellow for 10 minutes. At the first reasonable hour of the day, 7:00AM, it finally turns green. In reading the code, we noticed that it also goes red at 8:00PM for 45 minutes, which tells us it also functions as a go-to-sleep indicator.

When his son is a little older, maybe [JohnathonT] could build him  a clock that associates colors with activities.