Shift Register Powered Realistic Candle Flicker

[Kevin Darrah] recently went out to dinner at a restaurant that was using some cheap LED candles (yuck) instead of the real thing. And in the true spirit of a hacker, he started to notice the patterns programmed into the fake flame repeat over and over again. And like any hacker might, his mind started to devise a better way.

Now’s the time where some of us lazy hackers might grab a microcontroller, and copy and paste in some pseudo-random number generating code you found on the Internet, but not [Kevin]. The basics of his hack uses two shift registers tied together that are fed a single clock signal, and also a latch signal that is slightly delayed version of the same signal made by a RC-time circuit.

The randomness of the output is created is by feeding back the outputs of the shift registers to an XOR gate. If you want to learn more about this, the technique it’s called a “linear feedback shift register“. It’s commonly used as a poor-man’s random number generator, although it’s not technically truly random, statistically it does a very good job. You can see the results in the video after the break where [Kevin] describes the circuit.  He wraps up the hack with a battery and solar charging circuit as well to make a completed project.

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Cheap Function Generator Teardown and Improvement

In general, you get what you pay for, and when [Craig] picked up a cheap function generator off eBay, he didn’t expect much from it. But as he shows us in his blog post and a series of videos below, while the instrument lived down to his expectations, he was able to fix it up a bit.

Having spent only $100USD for the MHS-5200A, [Craig]’s adventure is a complete teardown and analysis of the function generator. While it sort of lives up to its specs, it’s pretty clear that some design decisions resulted in suboptimal performance. At higher frequencies and higher amplitudes, the sine wave output took on a markedly non-sinusoidal character, approaching more of a triangle waveform. The spectrum analyzer told the tale of multiple harmonics across the spectrum. With a reverse-engineered schematic in hand, he traced the signal generation and conditioning circuits and finally nailed the culprit – an AD812 op-amp used as the final amplifier. An in-depth discussion of slew rate follows in part 2, and part 3 covers replacement of the dodgy chip with a better selection that improves the output signal. We’re also treated to improvements to a low-pass filter that fixed a nasty overshoot and ringing problem with the unit’s square wave function.

If hacking the MHS-5200A seems a bit familiar to you, that’s because we covered another reverse-engineering exploit of it recently. That hack of the serial protocol of the instrument was by [WD5GNR], also known as Hackaday’s own [Al Williams]. Cheers to both [Craig] and [Al] for showing us what you can do with a hundred bucks and a little know-how.

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Hackaday Prize Entry: Feral Cats Phone Home with Das Katzetelegraf

Feral cats are a huge problem in some areas. Roaming freely in cities and in rural settings and reproducing with reckless abandon, colonies of feral cats can exhibit nuisance behavior that often results in unpleasant measures being taken to control their population. More humane programs, such as trap-neuter-return (TNR), seek to safely trap cats, give them basic vaccinations and neuter them, and either return them to their colony or, for a lucky few, ready them for adoption. Such programs are proving successful, but are not without issues. Enter Das Katzetelegraf.

You don’t need to understand a lick of German to figure out exactly what Das Katzetelegraf does from its name. Consisting of an Arduino, a GSM module, and a simple magnetic reed switch attached to the door of a humane cat trap, Das Katzetelegraf sends a text message to a TNR program volunteer when a cat has been trapped. Instead of waiting in the trap for the TNR workers to make daily rounds, the cats are quickly retrieved and the trap is reset for the next cycle. This reduces the time the cat spends in the trap, stressed and without access to food or water, and improves the animal’s outcome. As a bonus, each trap’s throughput is increased, so more animals can be cycled through the TNR program.

TNR can really help reduce feral cat populations, and Das Katzetelegraf can make them even more effective. But if you just have a stray cat pooping up your garden, a Raspberry Pi cat-deterring sprinkler might be a better choice.

The 2015 Hackaday Prize is sponsored by:

Fight Frost with an Internet of Things Fridge Alarm

It has been incredibly humid around these parts over the last week, and there seems to be something about these dog days that makes you leave the fridge or freezer door open by mistake. [pnjensen] found this happening all too often to the family chill chest, with the predictable accretion of frost on the coils as the water vapor condensed out of the entrained humid air and froze. The WiFi-enabled fridge alarm he built to fight this is a pretty neat hack with lots of potential for expansion.

Based on a Sparkfun ESP8266 Thing and home-brew door sensors built from copper tape, the alarm is rigged to sound after 120 seconds of the door being open. From the description it seems like the on-board buzzer provides a periodic reminder pip while the door is open before going into constant alarm and sending an SMS message or email; that’s a nice touch, and having the local alarm in addition to the text or email is good practice. As a bonus, [pjensen] also gets a log of each opening and closing of the fridge and freezer. As for expansion, the I2C header is just waiting for more sensors to be added, and the built-in LiPo charger would provide redundancy in a power failure.

If frost buildup is less a problem for you than midnight snack runs causing another kind of buildup, you might want to check out this willpower-enhancing IoT fridge alarm.

Programmable DC Backup Power Supply

The uninterruptible power supply was once a standard fixture in the small office/home office as a hedge against losing work when the electrons stop flowing from your AC outlet. Somewhat in decline as computing hardware shifts away from dedicated PCs toward tablets, phones and laptops, the UPS still has a lot of SOHO utility, and off-the-shelf AC units are easy to find. But if your needs run more to keeping the electrons flowing in one direction, then you might want to look at [Kedar Nimbalkar]’s programmable DC backup power system.

Built inside a recycled ATX power supply case, [Kedar]’s project is heavy on off-the-shelf components, like a laptop power supply for juice, a buck converter to charge the 12 volt sealed lead acid battery, and a boost converter to raise the output to 19.6 volts. An Arduino and an optoisolator are in charge of controlling the charging cycle and switching the UPS from charging the battery to using it when mains voltage drops.

 If you need a DC UPS but would rather skip the battery, you could try running a Raspberry Pi with electrons stashed in a supercapacitor. Or if you’ve got an aging AC UPS, why not try beefing it up with marine batteries?

[Thanks for the tip, Morris]

Building an Atomic Force Microscope on the Cheap!

LEGO2NANO, are building an open hardware AFM (Atomic Force Microscope).

AFMs are a kind of probe microscope. Unlike an optical microscope, a probe is used to “feel” the topology of a surface. An atomic force microscope uses a flexible cantilever with a nanometer scale tip on the end. As the tip scans across the surface it will be deflected by its interaction with the surface. A laser spot is usually reflected off the back of the cantilever, and captured by a photodiode array. The angle of the reflected beam, and therefore which photodiodes are excited lets you know how much the cantilever was deflected by the surface.

One of the challenges of building an AFM is developing an actuator that can move with nanoscale precision. We recently reported on [Dan Berard]s awesome capacitor actuator, and have previously reported on his STM build which uses a piezo buzzer. LEGO2NANO are experimenting with a number of different configurations, including using Piezo buzzers, but in a different configuration to [Dan]s system.

The LEGO2NANO project runs as a yearly summer school to encourage high school students to take part in the ambitious task of building an AFM for a few hundred dollars (commercial instruments cost about 100,000USD). While the project isn’t yet complete, whatever the outcome the students have clearly learned a lot, and gained an exciting insight into this cutting edge microscopy technique.

Hack Your Own Analog Camera

We remember making pinhole cameras as kids out of cigar boxes. The Focal Camera website wants to enable you to make sophisticated cameras from a selection of building blocks. We’re talking cameras with film, not digital cameras (although we wondered if you could mount an image sensor… but that’s another hack).

The modules do require access to a laser cutter, and you’ll need to scrounge or otherwise acquire things like mirrors and lenses. The site has advice on how to hack things like first surface mirrors out of cheap items like acrylic mirrors.

The intent is to be able to build up your own cameras from the modules. They do have a pinhole camera, in case you are nostalgic, but you could also build SLRs, large format cameras, or even stereo cameras. Not all the modules are ready yet, but there are several example cameras and pictures taken with them on the site. Like most building blocks, the real treat will be when users begin to combine them in unexpected ways.

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