Category Archives: filter

Shoot the Eclipse with a Phone and Do Not Go Blind

So you want to photograph Eclipse 2017 but you don’t want to rush out and buy an expensive DSLR just for the event? Not a problem, if you build this simple smartphone filter and occluder.

It all started innocently enough for [Paul Bryson] with his iPhone and a lens from those cheap cardboard eclipse glasses we’re starting to see everywhere. Thinking that just taping the filter over the stock lens would do, [Paul] got a painful faceful of sunshine when he tried framing a shot. Turns out the phone body was not big enough to blot out the sun, and …read more

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Posted in digital cameras hacks, Eclipse 2017, filter, iphone, partial, solar eclipse, telephoto, totality | Leave a comment

Cascade LNAs and Filters for Radioastronomy with an SDR

It may not be the radio station with all the hits and the best afternoon drive show, but 1420.4058 MHz is the most popular frequency in the universe. That’s the electromagnetic spectral line of hydrogen, and it’s the always on the air. But studying the H-line is a non-trivial task unless you know how to cascade low-noise amplifiers and filters to use an SDR for radio astronomy.

Because the universe is mostly made of hydrogen, H-line emissions are abundant, and their distribution can tell us a lot about the structure of galaxies. The 21-cm emission line is so characteristic and …read more

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Posted in filter, H-line, hydrogen, LNA, microwave, misc hacks, radio hacks, radioastronomy, spectrum | Leave a comment

Bessel Filter Design

Once you fall deep enough into the rabbit hole of any project, specific information starts getting harder and harder to find. At some point, trusting experts becomes necessary, even if that information is hard to find, obtuse, or incomplete. [turingbirds] was having this problem with Bessel filters, namely that all of the information about them was scattered around the web and in textbooks. For anyone else who is having trouble with these particular filters, or simply wants to learn more about them, [turingbirds] has put together a guide with all of the information he has about them.

For those who …read more

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Posted in analog, audio, bessel, design, digital audio hacks, filter, guide, how-to | Leave a comment

Rapidly Prototyping RF Filters

RF filters are really just a handful of strategically placed inductors and capacitors. Yes, you can make a 1 GHz filter out of through-hole components, but the leads on the parts turn into inductors at those frequencies, completely ruining the expected results in a design.

The solution to this is microstrip antennas, or carefully arranged tracks and pads on a PCB. Anyone can build one of these with Eagle or KiCad, but that means waiting for an order from a board house to verify your design. [VK2SEB] has a better idea for prototyping PCB filters: use copper tape on blank …read more

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Posted in filter, microstrip, microstrip filter, misc hacks, pcb, radio, RF, rf filter, wireless hacks | Leave a comment

Kill the Exhaust, Not Your Lungs with the Fume Coffin

As if slinging around 40 watts of potentially tattoo-removing or retina-singeing laser beams wasn’t anxiety-inducing enough, now comes a new, scary acronym – LCAGs, or “laser-generated airborne contaminants.” With something that scary floating around your shop, it might be a good idea to build a souped-up laser cutter exhaust fan to save your lungs.

We jest, but taking care of yourself is the responsible way to have a long and fruitful hacking career, and while [patternmusic]’s “Fume Coffin” might seem like overkill, can you go too far to protect your lungs? Plywood and acrylic, the most common materials that come …read more

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Posted in air cleaner, carcinogens, charcoal, exhaust, fan, filter, green hacks, HEPA, laser cutter, laser hacks, LCAG, particulates | Leave a comment

Say It With Me: Aliasing

Suppose you take a few measurements of a time-varying signal. Let’s say for concreteness that you have a microcontroller that reads some voltage 100 times per second. Collecting a bunch of data points together, you plot them out — this must surely have come from a sine wave at 35 Hz, you say. Just connect up the dots with a sine wave! It’s as plain as the nose on your face.

And then some spoil-sport comes along and draws in a version of your sine wave at -65 Hz, and then another at 135 Hz. And then more at -165 …read more

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Posted in aliasing, Engineering, filter, hackaday 101, Hackaday Columns, how-to, howto, nyquist, sampling | Leave a comment