# Christmas Star Uses Two AA Batteries

When [hkdcsf] was a teenager, he made a Christmas star with an up counter driving decoder logic and using transistors to light LEDs in festive patterns. He’s revisited this project using modern techniques including a microcontroller, a DC/DC converter, and constant current LED drivers.

The project uses two AA batteries, and that’s what makes the DC/DC converter necessary. Blue LEDs have a forward voltage of just over 3V, and the LED driver chip requires about 0.6V of overhead. Two fresh AAs will run a tad above 3V, but as they discharge, or if he’s using rechargeables, there just won’t be enough potential. To make sure the star works even with whatever LEDs are chosen, the converter takes the nominal 3V from the batteries and converts it to 3.71V.

# Mains Powered 3D Printer Heated Beds

Converting mains voltage down to 12 or 24VDC to drive a heating element makes no sense. To get 120 watts at 12 volts requires thick wires that can handle 10 amps, whereas at 120V, tiny 1A wires will do. If you’ve ever felt the MOSFET that switches your heated bed on and off, you know it’s working hard to pass that much current. [Makertum] is of the opinion this is a dumb idea. He’s creating a 110 / 230 V, mains-powered heated bed.

Creating a PCB heat bed isn’t an art – it’s a science. There are equations and variables to calculate, possibly some empirical measurements by measuring the resistance of a trace, but Ohm’s Law is a law for a reason. If you do things right, you can make a PCB heat bed perfectly suited for the task. You can even design in safety features like overcurrent protection and fuses. It can’t be that hard. After all, your house is full of devices that are plugged into the wall.

However, there’s a reason we use 12V and 24V heated beds – they give us, at the very least, the illusion of safety. Therefore, [Makertum] is looking for a few comments from specialists and people who know what they’re doing.

Although a mains powered heated bed sounds scary for a hobbyist-built 3D printer, there are a number of positives to the design. It would heat up faster, thin down a few parts, and significantly reduce the overall cost of the printer by not requiring another 100 Watts delivered from a 12V power supply. It’s a great idea if it doesn’t burn down the house. Anyone want to help?

# Toilet Automatically Flushes For Your Bathroom Trained Kitty

So you’ve successfully taught your cats to use your toilet, just like little furry humans. Congratulations! But you can’t quite teach the cat to pull the flush lever? You might want to automate it for them instead! (Editor’s note, 2019.  Link seems to be dead. Try the Wayback Machine.)

[Joycelin & Dan] are in the final stages of teaching their cats to use the toilet. Unfortunately they had a snowboarding trip coming up, and were worried about the cats losing progress when they couldn’t flush the toilet for them. Rather than have a bit of a setback in their toilet training, they improvised — and automated the toilet.

There are commercial solutions available, but they cost several hundred dollars. You could strap a geared motor to the side of your toilet with a stick screwed to it like this guy did, but who wants to pay for the water bill of flushing your toilet every few minutes??

# Decypering The Hackaday.io Illuminati

A few months ago, a strange account popped up on hackaday.io. Whoever is behind this count is based in Bielefeld, Germany – a place that doesn’t exist. They are somehow related to the Berenstain / Berenstein Bears dimensional rift, and they may be responsible for giving Cap’n Crunch only three rank insignia on his uniform. There is something very, very strange about this account. Since August, a black and white image of static, 98 pixels wide and 518 pixels tall has sat on this account profile. The Illuminati has given us enough clues, but until now, no one has managed to crack the code.

The first person to make sense out of the patterns in static is [Moritz Walter]. What’s in the code? More codes. While that’s not really helpful, it is to be expected.

The hackaday illuminati included one additional piece of information with their encoded static image: a 12×12 pixel bitmap. When this bitmap was XORed with the main image, symbols appeared. In total, there are only seven unique symbols in the image. These symbols seem to be stolen from the Fez alphabet, but there are some significant differences. These symbols are rotated multiples of 90 degrees, and are surrounded by a one pixel border that is either black or white (we’re calling the border a ‘sign’ bit). In total, these seven symbols arranged in four different rotations with two different signs yields forty unique variations of a symbol in the decoded image. At this point, it should be noted 7*2*4 = 56.

As of now, cracking the illuminati’s cyphered machinations has hit a roadblock. There’s a dead image file on the illuminati’s profile. Until that image is rehosted, there is no way to progress any further. That’s not going to stop people from trying, though: the chat channels on hackaday.io have been buzzing about the newly decrypted images. Hopefully, with time, someone will figure out what it all means.

# Rory Aronson On Documenting Open Source Projects

Every project starts off with an idea. Sometimes those ideas are bigger than one person, or even a small group of people. That was the position [Rory Aronson] found himself in with Farmbot, his finalist entry in the 2015 Hackaday Prize. Documentation was key for [Rory]. Farmbot first came into the world in the form of a white paper. The paper included a request for collaborators, making this an open source project from day 0. Documentation has been important throughout the Farmbot project, so it was naturally the topic of [Rory’s] talk at the 2015 Hackaday SuperConference.

# Taking The Pulse (Width Modulation) Of An FPGA

I like to think that there are four different ways people use FPGAs:

1. Use the FPGA as a CPU which allows you to add predefined I/O blocks
2. Build custom peripherals for an external CPU from predefined I/O blocks
3. Build custom logic circuitry from scratch
4. Projects that don’t need an FPGA, but help you learn

I’d bet the majority of FPGA use falls into categories one and two. Some FPGAs even have CPUs already built-in. Even without an onboard CPU, you can usually put a CPU “core” (think reusable library) into the chip. Either way, you can always add other cores to create UARTs, USB, Ethernet, PWM, or whatever other I/O you happen to need. You either connect them to a CPU on the chip, or an external one. With today’s tools, you often pick what you want from a list and then your entire project becomes a software development effort.

# Chewing Gum Plus Carbon Nanotubes

Normally, strain sensors are limited in their flexibility by the underlying substrate. This lead researchers at the University of Manitoba to an off-the-wall solution: mixing carbon nanotubes into a chewing-gum base. You can watch their demo video below the break.

The procedure, documented with good scientific rigor, is to have a graduate student chew a couple sticks of Doublemint for half an hour, and then wash the gum in ethanol and dry it out overnight. Carbon nanotubes are then added, and the gum is repeatedly stretched and folded, like you would with pizza dough, to align the ‘tubes. After that, just hook up electrodes and measure the resistance as you bend it.

The obvious advantage of a gum sensor is that it’s slightly sticky and very stretchy. The team says it works when stretched up to five times its resting length. Try that with your Power Glove.

We’ve seen a couple different DIY flex sensor solutions around these parts, one based on compressing black conductive foam and another using anti-static bags, but the high-tech, low-tech mixture of nanotubes and Wrigley’s is a new one.