Author: Al Williams

4338 Articles

A Fuse Is Just A Fuse, Right?

July 5, 2023 by 39 Comments

We like to think that most common electronic components are essentially commodity items. We don´t buy premium wire or resistors. You just assume these electronic components are more or less the same from anywhere unless you need some very special characteristics. What about fuses? We would assume they are all essentially the same, but [Ham Radio A2Z] says he’s throwing away his generic fuses after he found they didn’t work as he would expect.

Of course, name-brand fuses are tested to very specific tests, and you get to see the plots of how the fuses are supposed to melt for Bussmann fuses. Then he takes out a generic assortment of fuses he bought at a hamfest. No Bussmann fuses in that batch!

Comparing the generic fuses with some from Bussmann and Littlefuse, they all work fine to carry current. That isn’t the problem. The problem is when you feed the fuses 20 A and expect them to clear. A 5 A generic fuse carried over 20 A for a very long time, and, as you might expect, it got very hot. We kept waiting for the fuse to blow, but after three minutes, he gave up.

For comparison, a 10 A Bussmann fuse in the same conditions blew almost immediately — about 350 milliseconds. None of the generic fuses blew, and, in fact, the fuse in the video had been subjected to 20 A of over-stress several times already. It seems like it is nearly impossible to blow them at that current level despite it being four times the marked current. Not much of a bargain.

As the video points out, fuses aren’t as much to protect your equipment as much as they are to prevent fires, so don’t forget to include them even on simple projects. Remember the TI 99/4A? The power supply for that vintage computer has an odd little box in the power cable very near the plug. Why? Because they forgot to put a fuse in until the UL reminded them.

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Cheap Ham Radio Improves The Low End UI If Not The RF

July 5, 2023 by 17 Comments

There was a time when buying a new radio was something many hams could never afford to do. Then came the super cheap — and super controversial — VHF and UHF radios from China. But as they say, you get what you pay for. The often oddly named handhelds like Baofeng and Wouxun are sometimes odd to work with and may have questionable RF outputs. A new radio has a less tongue-twisting English name and many improved features for about $50 — the Talkpod A36Plus and [Josh] shows us how they work in a video that you can see below.

The new features are generally good. For example, the radio can pick up AM in the aircraft band, something most of these cheap radios won’t do. It works on VHF and UHF bands but also picks up FM broadcasts. The USB-C connector is welcome, and the screen is large and colorful. It has 500 channels and IP5 water resistance.

There were a few issues, though. If you want to use it as a scanner, it’s not very fast. The radio comes with a programming cable, but apparently, it uses an odd USB chipset that may give you some driver issues. The biggest problem, though, is that it has, according to the video, excessive spurious emissions. The power isn’t that high, and the antenna probably filters off some of it, too. But creating interference across the band isn’t very polite.

How bad are the harmonics? Well, [Josh] hooks up a spectrum analyzer and also shows how a radio tuned to the second harmonic easily picks up the transmission. Of course, no radio is perfect, but it seems like it does have very strong harmonic emissions. Of course, it may or may not be any worse than similar cheap radios. They are probably all above the legal limits, and it is just a matter of degrees.

These little radios won’t directly work the world — you need an HF radio for that, generally. They will let you connect to local repeaters, though. Some of those cheap radios can lead to interesting projects, too.

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Windows 10 The Hard Way: On A Phone

July 4, 2023 by 19 Comments

Sure, there are — or were — Windows phones. But [neozed] wanted something different. An earlier project ran Windows 10 on the Raspberry Pi 4 with some tricks, but those are sometimes hard to come by lately, so the next project was to put one on a Xiaomi PocoPhone F1.

The choice of phone wasn’t an accident. There was enough support and information on the Snapdragon 845 to pull the trick off, and this is one of the phones that looked like it should work. They were pretty inexpensive on eBay and have 128 GB of flash and 6 GB of RAM.

After a few false starts, the phone yielded to fastboot mode. Loading UEFI firmware allows you to re-partition the disks using a PC. With the partitions set up, you must find an ARM Windows 10 image to load. Sounds simple, but as you’ll see in the post, the devil is always in the details. Combined with a USB dock, the end result is a tiny Windows computer. However, it does seem like a lot of work. Even the original poster says: “TL;DR don’t do it… get a used Surface X instead.”

We’ve seen old phones repurposed before, of course. Or, go the other way: start from scratch and build a new phone. We won’t judge, either way.

Pratt Parsing For Algebraic Expressions

July 3, 2023 by 10 Comments

Parsing algebraic expressions is always a pain. If you need to compute, say, 2+4*2, the answer should be the same as (2 + (4 *2)), not ((2 + 4) * 2) — in other words, the right answer is 10, not 12. The classic way to do this is to use two stacks and a table of precedences for the operators. However, [Martin Janiczek] prefers to use Pratt Parsers and wants to show you how they work.

The parser is named after [Vaughn Pratt]. The algorithm works with a table of precedence where operators with higher precedence have higher numbers. It then builds a left and right portion of a string, using recursion. So if you consider 2+4*2, you wind up, on the first pass, with (2+ parse(4*2)). The second parse returns a full expression to produce: (2+(4*2)).

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The Chess Computer From 1912

July 3, 2023 by 12 Comments

Who was [Leonardo Torres Quevedo]? Not exactly a household name, but as [IEEE Spectrum] points out, he invented a chess automaton in 1920 that would foreshadow the next century’s obsession with computers playing chess.

Don’t confuse this with the infamous Mechanical Turk, which appeared to be a chess computer but was really a guy hiding inside a fake chess computer. The Spanish engineer’s machine really did play a modified end game. The chessboard was vertical, and pegs represented pieces. There were mechanical arms to move the pegs. The device actually dates back to 1912, with a public demonstration in Paris in 1914. Given [Quevedo’s] native language, the machine was called El Ajedrecista.

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Freq Out With LTSpice

July 3, 2023 by 4 Comments

We always enjoy [FesZ’s] videos, and his latest about FREQ function in LTSpice is no exception. In fact, LTSpice doesn’t document it, but it is part of the underlying Spice system. So, of course, you can figure it out or just watch the video below. The FREQ keyword allows you to change component attributes in a frequency-depended way.

Of course, capacitors and inductors are frequency dependent by design. But the FREQ technique allows you to adjust things like voltage sources or resistance in arbitrary ways. By default, you must specify the frequency response data in decibels, which isn’t always convenient. However, [FesZ] shows you how to use other methods to express them using modifiers to the command.

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Vintage Computer Festival Southwest: Bil And Al’s Excellent Adventure

June 30, 2023 by 12 Comments

There was a time when seeing an actual computer was a big deal. They were in air-conditioned rooms with raised floors and locked doors. Even at a university, you were likely only to get access to a keypunch machine or a terminal. Then small computers came out, but computer stores were few and far between. Now you can go to any local store that sells electronics and put your hands on hardware that would have been black magic in those days. But the computers back then were also much easier to understand completely. Look at your main computer today. Do you know all the assembly language instructions for it? Can you access the GPU and the MMU? Could you build your own memory for it? Sure, you don’t have to do those things, but it was fun knowing that you could. That seemed to be the overwhelming sentiment among the attendees we spoke to at the Vintage Computer Festival last weekend: We like computers that we can completely understand and troubleshoot.

If you weren’t one of the 900 or so attendees, we can help. Check out our video summary, dive into even more interviews with Bil Herd and guests on our YouTube channel, or just keep reading. The festival happens at several locations throughout the year, but this was the first time one has been in the Southwest for about ten years!

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