![[Usagi Electric] brandishing his raygun](https://hackaday.com/wp-content/uploads/2025/11/Usagi-Electric-Raygun-banner.jpg?w=800)
The Bomem DA3 is a type of Fourier transform spectrometer used for measuring various spectral data and [Usagi Electric] has one. On his quest to understand it he runs down a number of rabbit holes, including learning about various barcode formats, doing a teardown of the Telxon LS-201 barcode scanner, and exploring how lasers work. That’s right: lasers!
His reason for looking at the Telxon LS-201 barcode scanner is that it has the same type of helium-neon laser as his Bomem DA3 uses. Since he’s learning about barcode scanners he thinks it’s prudent to learn about barcode formats too, and he has a discussion with our very own Adam Fabio about such things, including the UPC-A standard barcodes.
It’s fun seeing the mainboard of the Telxon LS-201 sporting the familiar 555 timer, LM393 comparator, and three op-amps: 5532, LF347, and TL062; no discrete logic in sight! If you’re interested in barcode tech you might like to read Barcodes Enter The Matrix In 2027 and Old Barcode Scanner Motherboards Live Again. The particular Hackaday article mentioned in the video is this one: The Eloquence Of The Barcode.
Also, in the interest of public health and safety, make sure you’re wearing laser protection glasses if you’re working with laser technology. Even low power lasers can do damage to your eyes. Laser emissions can be invisible to the human eye and you don’t have nerves that tell you when your eyeballs are being roasted, so take care out there!
The barcode reader pistol looks like the head of K-9, the Doctor Who robot dog :-D
I have construction plans to make real Daleks and real Tardises, but are there any for K9? I always thought he was one of the best sidekicks – Orac being another one.
I hope you aren’t making real ones unless you have a real Doctor growing in a tube to keep the Daleks from wiping us out or enacting some sort of existential horror.
And what is worse… it has been proved that a bunch of stairs aren’t enough anymore to stop them!
Massive shout-out for Hackaday in the video!
I love his infectious enthusiasm.
That stabilized HeNe in the Bomem is actually pretty special: the heater is part of the lock loop, where the inputs are a pair of photodiodes looking at opposite (horizontal vs vertical) polarizations of the output HeNe light, and effectively are a quadrature pair sensor. They feed a feedback loop that powers the heater to make the laser tube a fixed number of wavelengths long. It makes a seriously precise and accurate wavelength reference that can be used to calibrate (e.g.) a spectrometer.
In a previous millennium I used one to make a wavemeter for visible light that was good to about one part in 10^11. The ultimate limit is the (thermal) Doppler broadening of the HeNe line. There are more modern, accurate and precise techniques available now, but the stabilized HeNe was incredible bang for the buck back then.
That’s an interesting way to do it. I worked with a ring laser gyro system that used a mirror attached to a piezo element to adjust the cavity length to an integer number of wavelengths.
Well, to be the pedant, a laser cavity is always going to be an integer number of wavelengths long :-) The question is how many wavelengths (and thus, what is their exact wavelength).
What kind of laser was it? And was the gyro cavity actually part of the laser resonator cavity? I can see you would want to lock the gyro to the (separately stabilized) laser, and use the error signals as your rate measurement.
HeNe is a bit of a pain because it has positive gain over only a few dozen MHz, which sets a lower bound on the cavity length, and thus minimum size for the laser tube. That barcode reader in the video is pretty much it for minimum size.
I was reading this story and thinking this “Bowmen” must be a moving mirror type with the HeNe as the reference for measuring the mirror displacement. Pretty neat setup. In the early 1980’s I came into possession of the Edson Peck IR Interferometer that he built to measure dispersion of gases. It was a big instrument built into a custom optical table and a rack with lock-in amplifiers and power supplies for photo-multipliers, etc. and filled a room. I had the notion of using an FT type moving mirror to replace all of the gratings and painstaking and time consuming measurements. The computing part was a bottleneck at that time. Plus I was not sure I could get dispersion curves when done. At the time, NASA was very interested in IR dispersion signatures of various gas combinations to use with the instruments on space probes to the planets. This reworking of the interferometer would have produced the data, and quickly. Now it is part of the vast collection of unfinished projects.
Why is the word “laser” in quotes in the title of the article? The bar code scanner used a real laser, not a fake one like those used in “laser” tag guns. And it’s not a quote, so quotation marks really don’t belong there.
Because it is written by Dr. Evil.
Yeah those are Dr Evil air quotes. Freaking “lasers”. https://www.youtube.com/watch?v=INFavIUmhcE
Well, it is right in the name: John Elliot V = John lot Evil
lol. Light forces for life! ;)