Category Archives: General

Interesting (but disappointing) Mini Buck Boards

I needed some cheap little vregs recently and had run out of and/or lost all of my useful-value 780x linear parts, so I decided to look at what people in this century use. 

I found some little buck boards roughly the size of a TO-220 package that looked exciting. These particular ones are QSKJ Mini DC-DC Buck Step Down Module model “QS-1205CME-3A”, Vendor page here, mine were 5pcs/$9 from Amazon.

Upon analysis they have serious issues with regulating under load, so the hunt for something decent continues, but the form-factor and advertised feature set are really compelling.

Pros:

  • High-efficiency high-frequency synchronous buck instead of a linear heater^H^H regulator.
  • Solder-jumpers for 1.8,2.5,3.3,5,9,12V or a default (fiddly, tiny) adjustment pot output so you only have to stock one device – one easy-to-cut trace to disable adjustable mode.
  • Tolerates 4.5-24V input as long as out < in or so.
  • Good stability to input voltage variation.
  • ~0.25V drop-out.
  • Does appear to have a cutoff for over-current.
  • No perceptible ripple under various load conditions.

Cons:

  • Voltage regulation manages maybe 600mA at 5V before droop becomes unacceptable (<4.8v).

…and that makes it basically useless for most applications. Test data below the fold.

Maybe it could be resolved with appropriate external capacitors and/or offsetting the adjustable to regulate right at a known load or something, but not being drop-in really reduces their charm.

Anyone know of a similar offering that doesn’t suck at output regulation?
(Rel: Anyone know if any of the low-end electronic loads are worthwhile? I’m not looking to spend real-lab-instrument money, but it’s come up often enough lately that I want to be able to dissipate a couple 10s of Watts through a at least stepwise-controllable resistive load).

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I ran into a delightful irony trying to help a student get set up for the embedded systems lab I’m running this semester: Neither Keil MDK ARM (a first-class ARM development environment) nor the Stellaris ICDI Drivers (TI’s programming/debug interface … Continue reading

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ThinkPad 560E

Complete ThinkPad 560E system.

I’ve been idly looking for one of the mid-90s ThinkPads known to have perfect OpenStep/Rhapsody support for years as a fun collector piece, but been unwilling to pay eBay prices. The other week I scored a pristine IBM ThinkPad 560E for $20 in a Shopgoodwill auction, below is notes on getting it up and running, plus some relevant history and plans.

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Apple 12″ Macintosh RGB Monitor Recap

This post is a retro post on a retro topic – a repair I did in 2017 on a monitor made in 1991. I got a question about (probably) the same problem in another venue and realized I never put it online. I managed to dig up my pictures and notes, so there is useful information to be shared.

My 12″ RGB Display is getting sad.

The end of my (2016) post about Recapping my Macintosh LC I discovered that my matching Apple 12″ Macintosh RGB Monitor ( M1296 ) was going pear-shaped, and speculated that I’d need to recap it.

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I have a machine with SSH exposed on one high-numbered nonstandard port forwarded through a NAT. A few days ago I noticed some log noise about failed SSH logins and turned on fail2ban with sane defaults. It banned almost 300 … Continue reading

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Macintosh SE Health Check

I had my dear old Macintosh SE out for a health check as I slowly extract my vintage computer collection from the (unconditioned) place I’ve been keeping it at my parents house to the basement of the place I’m renting. It had a couple interesting findings that seem worth putting online, including another floppy drive rebuild and a slightly elaborate fan replacement.

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Why did a Banggood package I ordered on March 26 just appear in Bahrain on July 5, the same day it finally showed “Shipment picked up?” Did it just get packed into a container and loaded on whatever outgoing vessel … Continue reading

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College Advice from a University Instructor

I’ve seen a spate of articles pop up recently discouraging people from going to college in fall 2020 because of the COVID-19 pandemic situation. They’re mostly from self-mythologizing startup douches and/or carpetbaggers trying to sell alternative education products, so there isn’t much of value in them and I won’t be linking.

However, talking about them has me refining and recording the advice I give to prospective college students.
So in that interest, a list of my usual advice. Which is very, very explicitly prefaced with the usual “Opinions expressed are solely my own and do not express the views or opinions of my employer” disclaimer.

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Improvised Remote Instruction Tools

During the first week and change of our vast national COVID-19 induced remote teaching experiment I made some notes on practices and improvised some equipment that has proved useful, and seems worth sharing with others.

This two week period I’ve primarily been running lab sessions to help my herd of mostly-Sophomores do and get sign off for a digital design lab exercise using Verilog to implement state machines, adapted slightly from our usual lab at this time in the semester.

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SC’19

Even though I haven’t done any work in that area in years, I got pulled into the Supercomputing conference again this year.  Can’t complain, it’s always fun.  UK’s combined booth looked good this year

Far corner is a little updated TinyTitan style Raspberry Pi cluster with a interactive CFD demo running on it that the CCS folks have been playing with, that thing in the leading corner is a cute flip-dot “quantum computer” model we built as a front-end for a 16-bit instance of Hank’s parallel bit-pattern computing system that can do quantum algorithms efficiently on a conventional platform – set in the corner of the booth like

You don't need quantum physics to perform quantum compution. Change my mind.

He did surprisingly well with this approach.

The exhibit floor was even more dominated by cooling tech this year. Exciting finds are the coming of very open (Open Compute Project, Coreboot + Open Network Linux) white-box 100GBE switches at reasonable prices, Fujitsu’s A64fx ARM with SVE and obscene memory bandwidth parts actually landing in systems, and (just because it tickled me) pre-wired fully populated Clos topology 100G cable harnesses.  The other dominant species was AI woo; my body is ready for AI Winter 3.0.

Google photos album of my annotated show floor photos is here.

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