Author: Al Williams

4334 Articles

Precision Current Sources By The Numbers

November 14, 2025 by 5 Comments

It isn’t unusual to expect a precisely regulated voltage in an electronic project, but what about times when you need a precise current? Over on EDN, prolific [Stephen Woodward] explains how to use a precision Zener diode to get good results. [Stephen] takes you through the math for two topologies and another circuit that uses a pair of bipolar transistors.

You might wonder why you need a precise current source or sink. While it is nice to drive things like LEDs with a constant current, you probably don’t need ultra-precise currents. However, charging a capacitor with a constant current produces a very nice linear voltage ramp. When you use a resistor to bias collector current in a bipolar amplifier, you are just poorly imitating a constant current source, too. That’s just two of many examples.

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Meet Me On My Rotary Phone

November 14, 2025 by 8 Comments

We suspect kids today — and some adults — are confused about phone terminology. In today’s world, “hanging up” and “dialing,” for example, are abstract words without the physical reference that older people remember. But some people have a soft spot for the old rotary dial phones, including [Stavros], who wired a rotary phone to his computer for use on online meetings. Check out the video below.

He took an old rotary phone and wanted to program a Raspberry Pi Zero to act as a sound card and a keyboard. That way, he could connect to the meeting by picking up the handset and disconnect by hanging up. He also planned to read the dial and convert that into keyboard input.

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WWII Secret Agents For Science

November 14, 2025 by 9 Comments

We always enjoy [History Guy]’s musing on all things history, but we especially like it when his historical stories intersect with technology. A good example was his recent video about a small secret group during the Second World War that deployed to the European Theater of Operations, carrying out secret missions. How is that technology related? The group was largely made of scientists. In particular, the team of nineteen consisted of a geographer and an engineer. Many of the others were either fluent in some language or had been through “spy” training at the secret Military Intelligence Training Center at Camp Ritchie, Maryland. Their mission: survey Europe.

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Cheap Multimeter Gets Webified

November 12, 2025 by 14 Comments

[Mellow Labs] wanted to grab a multimeter that could do Bluetooth. Those are cheap and plentiful, but the Bluetooth software was, unsurprisingly, somewhat lacking. A teardown shows a stock Bluetooth module. A quick search found a GitHub with software. But then he had a fiendish idea: could you replace the Bluetooth module with an ESP32 and use WiFi instead of Bluetooth?

This was as good an excuse as any to buy a cheap logic analyzer. Armed with some logic captures, it was easy to figure out how to fake the meter into thinking a Bluetooth client was connected.

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Morse Code For China

November 12, 2025 by 45 Comments

It is well known that pictographic languages that use Hanzi, like Mandarin, are difficult to work with for computer input and output devices. After all, each character is a tiny picture that represents an entire word, not just a sound. But did you ever wonder how China used telegraphy? We’ll admit, we had not thought about that until we ran into [Julesy]’s video on the subject that you can watch below.

There are about 50,000 symbols, so having a bunch of dots and dashes wasn’t really practical. Even if you designed it, who could learn it? Turns out, like most languages, you only need about 10,000 words to communicate. A telegraph company in Denmark hired an astronomer who knew some Chinese and tasked him with developing the code. In a straightforward way, he decided to encode each word from a dictionary of up to 10,000 with a unique four-digit number.

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Resurrecting Conquer: A Game From The 1980s

November 11, 2025 by 15 Comments

[Juan] describes himself as a software engineer, a lover of absurd humor, and, among other things, a player of Nethack. We think he should add computer game archaeologist to that list. In the 1990s, he played a game that had first appeared on USENET in 1987. Initially called “Middle-earth multiplayer game,” it was soon rebranded with the catchier moniker, Conquer.

It may not seem like a big thing today, but writing multiplayer software and distributing it widely was pretty rare stuff in the late 1980s or early 1990s. In 2006, [Juan] realized that this game, an intellectual predecessor to so many later games, was in danger of being lost forever. The source code was scattered around different archives, and it wasn’t clear what rights anyone had to the source code.

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Have A Slice Of Bumble Berry Pi

November 11, 2025 by 10 Comments

[Samcervantes] wanted a cyberdeck. Specifically, he wanted a Clockwork Pi uConsole, but didn’t want to wait three months for it. There are plenty of DIY options, but many of them are difficult to build. So [Sam] did the logical thing: he designed his own. The Bumble Berry Pi is the result.

The design criteria? A tactile keyboard was a big item. Small enough to fit in a pants pocket, but big enough to be useful. What’s more is he wanted to recycle some old Pi 3Bs instead of buying new hardware.

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