Fixing A PDP-11/03 Power Supply Is Easy When You Understand It

January 22, 2024 by Maya Posch 6 Comments

After we last saw [David Lovett] of [Usagi Electric], he was knee-deep in trying to fix a DEC PDP-11/03 power supply, which fortunately led to a fixed PSU and a very happy PDP-11/23 system installed in the enclosure, as he covers in today’s video. Previously, we had covered his debugging attempt of this very much dead power supply, which had led [David] down many fruitless rabbitholes. By the time he was taking various components off the board to try and induce certain results, he threw in the towel and went back to the drawing board, assisted with many community comments.

The 5V rail on a DEC PDP-11/03 power supply. (Credit: David Lovett)

Much of the confusion came down to not really understanding how this PDP-11/03 PSU design works, which isn’t that crazy in hindsight, considering how quaint it is. Although [David] originally focused on the +5V rail, a small detail that was in the schematics is that the 5V rail is based around a 7805 that has its ground referenced to the -15V rail.

It is this 7805 that provides a linearly regulated 5V rail up till its current limit, at which point the control transistor gets biased sufficiently to start conducting, which eventually triggers the driver transistor that is responsible for driving the pass switch transistor. This then charges L2 from the unregulated supply, which is used effectively as a switching mode power supply until the current across the 7805 drops sufficiently that it becomes the primary 5V rail source again. This repeats at a kHz rate, making it more or less an SMPS as we know it today, but heavily reliant on the -15V rail as can be observed in the schematic. Continue reading “Fixing A PDP-11/03 Power Supply Is Easy When You Understand It” →

Bell Labs Is Leaving The Building

January 22, 2024 by Al Williams 18 Comments

If you ever had the occasion to visit Bell Labs at Murray Hill, New Jersey, or any of the nearby satellite sites, but you didn’t work there, you were probably envious. For one thing, some of the most brilliant people in the world worked there. Plus, there is the weight of history — Bell Labs had a hand in ten Nobel prizes, five Turing awards, 22 IEEE Medals of Honor, and over 20,000 patents, including several that have literally changed the world. They developed, among other things, the transistor, Unix, and a host of other high-tech inventions. Of course, Bell Labs hasn’t been Bell for a while — Nokia now owns it. And Nokia has plans to move the headquarters lab from its historic Murray Hill campus to nearby New Brunswick. (That’s New Jersey, not Canada.)

If your friends aren’t impressed by Nobels, it is worth mentioning the lab has also won five Emmy awards, a Grammy, and an Academy award. Not bad for a bunch of engineers and scientists. Nokia bought Alcatel-Lucent, who had wound up with Bell Labs after the phone company was split up and AT&T spun off Lucent.

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3D Printed Screw Compressor Revisited

January 22, 2024 by Al Williams 12 Comments

[Indeterminate Design] tried to 3D print a screw compressor some time ago but wasn’t satisfied with the result. He’s trying it again, and you can check it out in the video below. You can also download the 3D printable files.

This isn’t a 3D-printed keychain. The screw threads have to mesh with a small space between them, and the design is not trivial. Even if you don’t want to build your own, the look inside the engineering behind these devices is interesting, and there is quite a bit of background about how the rotor’s shapes are optimized.

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Haier Europe Eases Off On Legal Threat And Seeks Dialogue

January 22, 2024 by Maya Posch 40 Comments

After initially sending a cease and desist order to [Andre Basche] – the developer of a Haier hOn plugin for Home Assistant – Haier Europe’s head of Brand and IoT has now penned a much more amicable response, seeking to enter into dialogue in search of a solution for both parties.

This latest development is detailed both in the ongoing GitHub issue, as well as the Takedown FAQ and Timeline document that [Andre] created to keep track of everything that’s going on since we last checked in on the situation. As things stand, there is hope that Haier Europe may relent, especially as the company’s US division has shown no inclinations to join in on the original C&D.

In the confusion following the initial C&D announcement demanding the take-down of [Andre]’s hOn-related repositories, it was not clear to many which Haier was involved. As it turns out, Haier Europe as a separately legal entity apparently decided to go on this course alone, with Haier US distancing themselves from the issue. In that same Reddit thread it’s noted that GE Appliances (part of Haier US) has had a local API available for years. This makes Haier Europe the odd one out, even as they’re attempting some damage control now.

Amidst this whirlwind of developments, we hope that Haier Europe can indeed reach an amicable solution with the community, whether it’s continued API usage, or the development of a local API.