Author: Al Williams

4388 Articles

Michelson Interferometer Comes Home Cheap

January 12, 2026 by 24 Comments

We suspect there are three kinds of people in the world. People who have access to a Michelson Interferometer and are glad, those who don’t have one and don’t know what one is, and a very small number of people who want one but don’t have one. But since [Longest Path Search] built one using 3D printing, maybe the third group will dwindle down to nothing.

If you are in the second camp, a Michelson interferometer is a device for measuring very small changes in the length of optical paths (oversimplifying, a distance). It does this by splitting a laser into two parts. One part reflects off a mirror at a fixed distance from the splitter. The other reflects off another, often movable, mirror. The beam splitter also recombines the two beams when they reflect back, producing an interference pattern that varies with differences in the path length between the splitter and the mirror. For example, if the air between the splitter and one mirror changes temperature, the change in the refraction index will cause a minute difference in the beam, which will show up using this instrument.

The device has been used to detect gravitational waves, study the sun and the upper atmosphere, and also helped disprove the theory that light is transmitted through a medium known as luminiferous aether.

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Design Of Common Emitter Amplifier

January 11, 2026 by 7 Comments

It used to be a rite of passage to be able to do the math necessary to design various bipolar transistor amplifier configurations. This doesn’t come up as often as it used to, but it is still a good skill to have, and [Void Electronics] walks us through a common emitter amplifier in a recent video you can see below.

The input design parameters are the gain and the collector voltage. You also have to pick a reasonable collector current within the range for your proposed device that provides enough power to the load. You also pick a quiescent voltage which, if you don’t have a good reason for picking a different value, will usually be half the supply voltage.

The calculations are approximate since the base-emitter voltage drop will vary by temperature, among other things. But, of course, real resistors won’t have the exact values you want, or even the exact value marked on them, so you need a little flexibility, anyway.

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The SCSI Film Scanner Resurrection

January 11, 2026 by 15 Comments

[Ronan] likes 35mm film photography, but the world, of course, has gone digital. He picked up an Epson FilmScan 200 for about €10. This wonder device from 1997 promised to convert 35mm film to digital at 1200 DPI resolution. But there was a catch: it connects via SCSI. Worse, the drivers were forever locked to Windows 95/98 and Mac System 7/8.

In a surprise twist, though, [Ronan] recently resurrected a Mac SE/30 with the requisite SCSI port and the System 7 OS. Problem solved? Not quite. The official software is a plugin for Photoshop. So the obvious answer is to write new software to interact with the device.

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ESP With EEG — No, Not That ESP!

January 10, 2026 by 13 Comments

While EEG research might help you figure out extrasensory perception, we won’t be betting on it. However, if you want to read EEG data and use an ESP32, [Cerelog-ESP-EEG] might be the right project for you. The commercial project is an 8-channel biosensing board suitable for EEG, EMG, ECG, and brain-computer interface studies. However, the company says, “We love the hacker community! We explicitly grant permission for Personal & Educational Use.” We love you too.

They do require you to agree not to sell boards you are building, and they give you schematics, but no PC board layout. That’s understandable, although we’d guess that achieving good results will require understanding how to lay out highly sensitive circuits.

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Multi-material Parts The Easy Way

January 10, 2026 by 14 Comments

You have a part that needs different colors or different material properties — with a multi-color 3D printer, no problem. You can also laboriously switch filaments on a single-color printer. But [anonymous kiwi] points out a different way, which is surprisingly obvious once you think about it. You simply add a previously made part to another one.

If you’ve ever experimented with adding a nut or a magnet into a print in the middle, the idea is exactly the same: you print one piece and then print a second piece, pausing in the middle to insert the completed first piece. The video example shows TPU robot wheels with PLA hubs. Of course, the same idea could apply to using different colors or even multiple materials or parts. You could imagine a hub with a steel nut embedded in it, then further being embedded in a TPU wheel, for example.

With multi-material printers becoming more commonplace, this technique might seem antiquated. But even if you have one of such a printer, this technique could save time and reduce waste. Not every part would work out this cleanly, but it is something to remember for the times when it does.

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Math Breakthrough Helps Your Feng Shui

January 9, 2026 by 34 Comments

In 1966, a mathematician named [Leo Moser] proposed what sounds like a simple problem: What’s the largest shape you can move through a 1-meter corridor with a right-angle corner? Now, Korean mathematics whiz [Baek Jin-eon] claims to have solved the problem, nearly 60 years later.

The trick is, apparently, the shape of the sofa. By 1968, [John Hammerley] introduced a shape that did better than a rectangle, and by 1992, [Joseph Gerver] proposed something shaped like a phone handset, which remains the largest anyone had found, at 2.2195 square meters.

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Seeing Sound With A Laser

January 9, 2026 by 16 Comments

You can hear sound, of course, but what if you could see it with a laser? That’s what [Goosetopherson] thought about, and thus a new project that you can see in the video below was born.

The heart of the project is an I2S chip and an ESP32. Sound energy deforms a plastic film that causes a mirror to move. The moving mirror alters the course of the laser’s beam. Continue reading “Seeing Sound With A Laser” →