Author: Al Williams

4160 Articles

MIT Wants You To Secure Your Hardware Designs

April 3, 2025 by 9 Comments

When you think of attacking or defending computer systems, you probably think of software viruses and the corresponding anti-virus software. But MIT’s 6.5950 class teaches secure hardware design — how to attack and defend CPUs from bad actors. Interested? The course is open source, so you can follow along as long as you don’t mind not getting a grade.

Browsing some of the lecture slides shows that the material isn’t as stuffy as you might imagine. A slide about side channel attacks, for example, features an article called “And Bomb the Anchovies,” which says that Washington DC pizza places know when big news is about to break because pizza delivery to places like the White House or the Pentagon trend upward (something spies call pizza-int, by the way).

Even if you don’t have a burning desire to design more secure hardware, some of the lecture slides make for an interesting flip through on a rainy weekend day. For example, the charts about RowHammer (“RowHammer in One Sentence”) is a great explanation about how software can cause DRAM failures to attack a computer. We only wished they’d identified companies A, B, and C in their study. There are also labs and they politely clarify what setup you need to do each lab (typically, just a Linux server, although some you can do with just a browser).

One of the great things about the Internet is that you can virtually audit classes from anywhere in the world, often for free. MIT is always up to something interesting.

The Magic Touch: A 555 Touch Switch

April 2, 2025 by 14 Comments

There seems to be nothing a 555 can’t do. We’ve seen it before, but [electronzapdotcom] reminds us you can use a 555 and a few parts to make a reasonable touch switch in this video, embedded below.

The circuit uses some very large resistors so that noise from your body can overcome the logic level on the trigger and threshold inputs. You can easily adapt this idea if you need a simple touch switch. Though we imagine this circuit wouldn’t work well if you were in a quiet environment. We suspect 50 or 60 Hz hum is coupling through your finger and triggering the pins, but it could be a different effect.

How reliable is it? Beats us. The circuit is a bistable, so essentially your finger pumps a signal into a flip-flop. This is old trick, but could be useful. Of course, if you really need a touch switch, you have plenty of options. You can get little modules. Or, directly measure skin resistance.

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Zink Is Zero Ink — Sort Of

March 31, 2025 by 37 Comments

When you think of printing on paper, you probably think of an ink jet or a laser printer. If you happen to think of a thermal printer, we bet you think of something like a receipt printer: fast and monochrome. But in the last few decades, there’s been a family of niche printers designed to print snapshots in color using thermal technology. Some of them are built into cameras and some are about the size of a chunky cell phone battery, but they all rely on a Polaroid-developed technology for doing high-definition color printing known as Zink — a portmanteau of zero ink.

For whatever reason, these printers aren’t a household name even though they’ve been around for a while. Yet, someone must be using them. You can buy printers and paper quite readily and relatively inexpensively. Recently, I saw an HP-branded Zink printer in action, and I wasn’t expecting much. But I was stunned at the picture quality. Sure, it can’t print a very large photo, but for little wallet-size snaps, it did a great job.

The Tech

Polaroid was well known for making photographic paper with color layers used in instant photography. In the 1990s, the company was looking for something new. The Zink paper was the result. The paper has three layers of amorphochromic dyes. Initially, the dye is colorless, but will take on a particular color based on temperature.

The key to understanding the process is that you can control the temperature that will trigger a color change. The top layer of the paper requires high heat to change. The printer uses a very short pulse, so that the top layer will turn yellow, but the heat won’t travel down past that top layer.

The middle layer — magenta — will change at a medium heat level. But to get that heat to the layer, the pulse has to be longer. The top layer, however, doesn’t care because it never gets to the temperature that will cause it to turn yellow.

The bottom layer is cyan. This dye is set to take the lowest temperature of all, but since the bottom heats up slowly, it takes an even longer pulse at the lower temperature. The top two layers, again, don’t matter since they won’t get hot enough to change. A researcher involved in the project likened the process to fried ice cream. You fry the coating at a high temperature for a short time to avoid melting the ice cream. Or you can wait, and the ice cream will melt without affecting the coating.

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Tiny Bubbles In The Memory

March 31, 2025 by 15 Comments

We are always fascinated by bubble memory. In the late 1970s, this was the “Next Big Thing” that, as you may have guessed, was, in fact, not the next big thing at all. But there were a number of products that used it as non-volatile memory at a time when the alternative was tape or disk. [Smbakeryt] has a cool word processor with an acoustic coupler modem made by Teleram. Inside is — you guessed it — bubble memory.

The keyboard was nonfunctional, but fixable. Although we wouldn’t have guessed the problem. Bubble memory was quite high tech. It used magnetic domains circulating on a thin film of magnetic material. Under the influence of a driving field, the bubbles would march past a read-write head that could create, destroy, or read the state of the bubble.

Why didn’t it succeed? Well, hard drives got cheap and fairly rugged. The technology couldn’t compete with the high-density hard drives that could be reached with improved heads and recording strategies. Bubble memory did find use in high-vibration items, but also wound up in things like this terminal, at least one oscilloscope, and a video game.

Bubble memory evolved from twistor memory, one of several pre-disk technologies. While they are hard to come by today, you can find the occasional project that either uses some surplus or steals a part off of a device like this one.

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Protocol Analyzer Remembered

March 30, 2025 by 22 Comments

Anyone will tell you that as hard as it is to create a working system, the real trick is making two systems talk to each other, especially if you created only one or none of them. That’s why tools that let you listen in on two systems talking are especially valuable.

If you were a well-funded lab back in the RS232 days, you might have an HP4957A protocol analyzer. The good news is that if you still use RS232, these kinds of things are now cheap on the surplus market. [IMSAI Guy] got one of these decidedly cool devices and shows it to us in the video below.

The look of these was pretty neat for their time—a folded-up instrument with a cute keyboard and a CRT-100. You can load different interpreters from ROM to RAM, such as the VT-100, which is essentially an application for the device. Of course, now you could rig one of these up in a few minutes with a PC or even a Pi Pico. But it wouldn’t have the same charm, we are sure you would agree.

You can find a lot of old RS232 gear around, from breakout boxes to advanced sniffers like this one. Too bad we couldn’t afford them when we really needed them.

This could be handy if you have a lot of ports. Either real or virtual. Or, do it yourself.

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Pictures From A High Altitude Balloon

March 28, 2025 by 14 Comments

How do you get images downlinked from 30 km up? Hams might guess SSTV — slow scan TV — and that’s the approach [desafloinventor] took. If you haven’t seen it before (no pun intended), SSTV is a way to send images over radio at a low frame rate. Usually, you get about 30 seconds to 2 minutes per frame.

The setup uses regular, cheap walkie-talkies for the radio portion on a band that doesn’t require a license. The ESP32-CAM provides the processing and image acquisition. Normally, you don’t think of these radios as having a lot of range, but if the transmitter is high, the range will be very good. The project steals the board out of the radio to save weight. You only fly the PC board, not the entire radio.

If you are familiar with SSTV, the ESP-32 code encodes the image using Martin 1. This color format was developed by a ham named [Martin] (G3OQD). A 320×256 image takes nearly two minutes to send. The balloon system sends every 10 minutes, so that’s not a problem.

Of course, this technique will work anywhere you want to send images over a communication medium. Hams use these SSTV formats even on noisy shortwave frequencies, so the protocols are robust.

Hams used SSTV to trade memes way before the Internet. Need to receive SSTV? No problem.

Tech In Plain Sight: Hearing Aids

March 26, 2025 by 38 Comments

You might think you don’t need a hearing aid, and you might be right. But in general, hearing loss eventually comes to all of us. In fact, you progressively lose hearing every year, which is why kids can have high-pitched ringtones their parents can’t hear.

You’d think hearing aids would be pretty simple, right? After all, we know how to pick up sounds, amplify them, and play them back. But there’s a lot more to it. Hearing aids need to be small, comfortable, have great battery life, and cram a microphone and speaker into a small area. That also can lead to problems with feedback, which can be very uncomfortable for the user. In addition, they need to handle very soft and loud sounds and accommodate devices like telephones.

Although early hearing aids just made sound louder and, possibly, blocked unwanted sound, modern devices will try to increase volume only in certain bands where the user has hearing loss. They may also employ sophisticated methods to block or reduce noise. Continue reading “Tech In Plain Sight: Hearing Aids” →