Such was the lesson learned by [CuriousMarc] with his recently restored Model 15 Teletype; we covered a similar Model 19 restoration that he tackled. The essential problem is that the five-bit Baudot code that they speak predates the development of ASCII by several decades, making a converter necessary. A task like that is a perfect job for an Arduino — [Marc] put a Mega to work on that — but the interface of the Teletype proved a bit more challenging. Designed to connect two or more units together over phone lines, the high-voltage 60-mA current loop interface required some custom hardware. The testing process was fascinating, depending as it did on an old Hewlett-Packard serial signal generator to throw out a stream of five-bit serial pulses.
The big moment came when he used the Teletype to log into Linux on a (more or less) modern machine. After sorting out the mysteries of the stty command, he was able to log in, a painfully slow process at 45.5 bps but still a most satisfying hack. The ASCII art — or is it Baudot art? — is a nice bonus.
We love restorations like these, and can practically smell the grease and the faint tang of ozone around this device. We’re not thrilled by the current world situation, but we’re glad [CuriousMarc] was able to use the time to bring off a great hack that honors another piece of our computing history.
Germicidal lamps are designed to destroy viruses and bacteria using ultraviolet light. But not just any UV light will work, and I came across an example of a lamp that was advertised as germicidal but a few things just weren’t right about it.
I ordered the UV-C germicidal LED lamp on Amazon, and received it a few days ago. It felt the suspicion from the first moment: playing around with a lot of different UV LEDs, I’ve learnt how the parasitic visible light from different UV ranges should look like to human eye. Also, proper UV-C LED lenses like the one shown here are made of quartz glass. Compare that to the image at the top of the article of the bulb I received that has a soft plastic lens, which is possibly opaque and degradable in the far UV range. The most important clue that something was wrong was the price. It’s hard to imagine that a UV-C LED lamp with the 253.7nm wavelength, made of more than 200 LEDs and in such a robust metal case, can cost only $62.99.
Although there was the risk of being unjust, I decided to return the product. In my message I bluffed that I measured the spectra of the lamp with a spectral emission meter, and that its output was not in the UV-C range. The next day I received confirmation that the bluff paid off: the seller replied that they advertised the product according to information from the supplier, and that the incorrect information was caused by their lack of understanding of product information. They also attached the official datasheet with the measured wavelength: it was not 253.7 nm, as advertised, but with the peak at 394.3 nm, and the dominant wavelength at 413.9 nm. It was not in the far UV-C, but in the near UV-A range and not at all useful for destroying germs! The seller promised that the product would be removed from their store, and kept the promise.
If you are thinking about buying a UV-C LED lamp, maybe you should get the good old CFL germicidal lamp. I don’t think that viruses care too much about the new technology.