All Inverters Are (Not) Created Equal

October 30, 2023 by Al Williams 10 Comments

Building a crystal clock source for a CPU used to be a bit of an effort but these days, there’s nothing to it. Even if your CPU or other device needs an external clock, you just slap in an inverter, a crystal, and two capacitors together, and you are done, right? Maybe not. [Dave Collins] got interested in the common circuit and pulled out his scope and an array of different kinds of inverters. He looked at inverters and NAND gates and a few common circuit configurations.

This is one of those things you just assume is of little importance, but it turns out your choice of circuit architecture and active device can have a big impact on the output. But who has time to do all the testing? Thanks to [Dave] you don’t have to.

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Ham Radio May Speed Up Soon

October 29, 2023 by Al Williams 14 Comments

The FCC is circulating a proposal for new rules pertaining to amateur radio in the United States. In particular, they want to remove certain baud rate restrictions that have been in place since 1980. It appears the relaxed rules would apply only to some bands, notably some VHF and UHF bands along with the 630 meter and 2200 meter bands, which — we think — are lightly used so far. We’ll save you from grabbing the calculator. That’s around 475 kHz and 136 kHz.

Ham radio operators have long used digital modes like radio teletype and with restrictions on antennas and increasing interference from wireless networking to solar panels and more, digital has become even more popular than in the past. Besides that, cheap computer soundcards make it easier than ever and sophisticated digital modulation techniques have long left the old, clunky TeleType in the dust.

However, the FCC currently limits the baud rate to 300 baud or less, ostensibly to restrict signal bandwidth. No one wants to have an entire band consumed by a 10 Gb RF network. However, modern techniques often squeeze more into less and the FCC will finally recognize that by converting the limit to signal bandwidth, not baud rate.

What’s the bandwidth? For the common bands, it sounds like 2.8 kHz is the answer. For the VLF bands, they are asking for suggestions. The 2200 meter band isn’t even 2.8 kHz wide to start with!

All this talk makes us want to build something for the 2200 meter band. We better start winding the coil now. Then again, maybe we should go piezo. You know, just in case Thomas Dolby tells us that one of our submarines is missing.

Simple Badge Is Simple, But It’s Yours

October 26, 2023 by Al Williams 8 Comments

Making conference badges, official or unofficial, has become an art form. It can get pretty serious. #badgelife.

But DEFCON-goers aren’t the only people making fancy personalized nametags. Hams often had callsign badges going back as far as I can remember. Most were made of engraved plastic, but, at some point, it became common to put something like a flashing LED on the top of the engraved antenna tower or maybe something blinking Morse code.

Going back to that simpler time, I wanted to see if I could make my own badge out of easily accessible modules. How easy can it be? Let’s find out. Along the way, we’ll talk about multicore programming, critical sections, namespaces, and jamming images into C++ code. I’ll also show you how to hijack the C preprocessor to create a little scripting language to make the badge easier to configure.

Bottom Line Up Front

The photo shows the Pico badge. It has an RP2040 CPU but not a proper Raspberry Pi Pico. The Waveshare RP2040-Plus clone has a battery connector and charger. It also has a reset button, and this one has 16 MB of flash, but you don’t need that much. The LCD is also a Waveshare product. (This just happened to work out. I bought all of this stuff, and I don’t even know anyone at Waveshare.) The only other thing you need is a USB C cable and a battery with an MX 1.25 connector on it with the correct polarity. Hardware done! Time for software.

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Linux Fu: Customizing Printf

October 24, 2023 by Al Williams 13 Comments

When it comes to programming in C and, sometimes, C++, the printf function is a jack-of-all-trades. It does a nice job of quickly writing output, but it can also do surprisingly intricate formatting. For debugging, it is a quick way to dump some data. But what if you have data that printf can’t format? Sure, you can just write a function to pick things apart into things printf knows about. But if you are using the GNU C library, you can also extend printf to use custom specifications. It isn’t that hard, and it makes using custom data types easier.

An Example

Suppose you are writing a program that studies coin flips. Even numbers are considered tails, and odd numbers are heads. Of course, you could just print out the number or even mask off the least significant bit and print that. But what fun is that?

Here’s a very simple example of using our new printf specifier “%H”:

printf("%H %H %H %H\n",1,2,3,4);
printf("%1H %1H\n",0,1);

When you have a width specification of 1 (like you do in the second line) the output will be H or T. If you have anything else, the output will be HEADS or TAILS.

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Retrotechtacular: The $175,000 Laser Printer

October 23, 2023 by Al Williams 38 Comments

Laser printers today are cheap and readily available. But in 1976, they were the height of printing technology. The IBM 3800 was the $175,000 printer to have in that year. (Video, embedded below.) But you couldn’t have one on your desktop. Even if you could afford it, the thing is the size of a car, and we don’t even want to guess what it weighs. The printer took tractor-fed continuous form paper and could do 167 pages a minute at about 150 dots per inch (actually 180 x 144). For the record, that was as much as 1.7 miles of paper an hour!

In those days, people who would use this printer traditionally had massive banks of noisy impact printers. We imagine this device saved many data processing person’s hearing. Compared to a modern laser printer, though, it needed a lot of maintenance. For example, the initial models needed a xenon flash lamp replaced every month, although later models could go years on one bulb. Looking at some of the hardware in the video, it was probably made closer to the end of life for these printers which were made through 1999.

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Is That A Record Player In Your Pocket Or…

October 23, 2023 by Al Williams 27 Comments

If aliens visited the Earth, they might find our obsession with music hard to fathom. We have music in our homes, our cars, and our elevators. Musical performances draw huge crowds and create enormous fame for a select few musicians. These days, your music player of choice is probably the phone in your pocket. What our grandparents wouldn’t have done to have a pocket-sized music player. Wait…, it turns out they had them. [Rare Historical Photos] has pictures and other material related to the Mikiphone — a “pocket phonograph.” We don’t know how it sounded, but it is a fantastic piece of work visually. Actually, thanks to the [Stanford Archive of Recorded Sound], you can hear one of these rare machines playing in the video below. If only it were playing Toni Basil.

The device was made in the 1920s and had a decidedly strange tonearm. You wind it up with a gigantic key mechanism. There’s no electricity. A bakelite resonator became the speaker attached to the tone arm. The device was made in Switzerland by a company that started in music boxes. However, the design was the work of two brothers named Vadász.

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Math Book Gets Real With Complex

October 22, 2023 by Al Williams 22 Comments

The [Math Sorcerer] loves books. His latest acquisition is the famous Real and Complex Analysis, which is a very stout math book. How stout? Well, there are several chapters on holomorphic functions, including how to do a Fourier transform on such a function. There’s also an appendix about Hausdorff’s maximality theorem. What are those? Beats us; read the book. You can also watch the short video review of the text below.

The author asserts right up front that the exponential function is “undoubtedly the most important function in mathematics.” Undoubtedly. [The Math Sorcerer’s] videos remind us of browsing a bookstore or a library. You don’t get a book summary as much as a preview of what’s in it, so you can decide if you want to read it.

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