Author: Al Williams

4386 Articles

Head To Head: Servos Vs Steppers

January 14, 2025 by 12 Comments

You have a project that needs something to move. Should you use a stepper motor or a servo motor? [Matthias] has an opinion, and you can hear his thoughts in the video below. One tip we’ll take away from the video: when working with motors, shoot some high-frame-rate video and slow it down to see what’s really happening.

The initial tests looked fine at normal speed. But increasing the frame rate and decreasing the playback speed showed some very interesting things like how much each motor was overshooting. The ability to control this sort of thing is a key differentiator for these kinds of motors.

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Gaming Table Has Lights, Action

January 12, 2025 by 2 Comments

We couldn’t decide if [‘s] Dungeons and Dragons gaming table was a woodworking project with some electronics or an electronics project with some woodworking. Either way, it looks like a lot of fun.

Some of the features are just for atmosphere. For example, the game master can set mood lighting. Presets can have a particular light configuration for, say, the woods or a cave.

But the table can also be a game changer since the game runner can send private messages to one or more players. Imagine a message saying, “You feel strange and suddenly attack your own team without any warning.”

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Retrotechtacular: The 1951 Telephone Selector

January 11, 2025 by 20 Comments

Telephone systems predate the use of cheap computers and electronic switches. Yesterday’s phone system used lots of stepping relays in a box known as a “selector.” If you worked for the phone company around 1951, you might have seen the Bell System training film shown below that covers 197 selectors.

The relays are not all the normal ones we think of today. There are slow release relays and vertical shafts that are held by a “dog.” The shaft moves to match the customer’s rotary dial input.

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The Engineer Behind Mine Detection

January 10, 2025 by 8 Comments

According to [Joanna Goodrich]  in IEEE Spectrum, prior to World War II, soldiers who wanted to find land mines, simply poked at the ground with pointed sticks or bayonets. As you might expect, this wasn’t very safe or reliable. In 1941, a Polish signals officer, [Józef Stanislaw Kosacki], escaped to Britain and created an effective portable mine detector.

[Kosaci] was an electrical engineer trained at the Warsaw University of Technology. He had worked as a manager for the Polish National Telecommunication Institute. In 1937, the government tasked him with developing a machine that could detect unexploded grenades and shells. The machine was never deployed.

When Germany invaded Poland in 1939, [Kosacki] returned to military service (he had done a year of compulsory service earlier). He was captured and kept in a prison camp in Hungary. But he managed to escape in late 1939 and joined the Polish Army Corps in Britain, teaching Morse code to soldiers.

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A Low Effort, Low Energy Doorbell

January 10, 2025 by 19 Comments

Bluetooth is a good way to connect devices that are near each other. However, it can drain batteries which is one reason Bluetooth Low Energy — BLE — exists. [Drmph] shows how easy it is to deploy BLE to make, in this case, a doorbell. He even shows how you can refit an existing doorbell to use the newer technology.

Like many projects, this one started out of necessity. The existing wireless doorbell failed, but it was difficult to find a new unit with good review. Cheap doorbells tend to ring spuriously due to interference. BLE, of course, doesn’t have that problem. Common BLE modules make up the bulk of the project. It is easy enough to add your own style to the doorbell like a voice announcement or musical playback. The transmitter is little more than a switch, the module, a coin cell, and an LED.

It is, of course, possible to have a single receiver read multiple doorbells. For example, a front door and back door with different tones. The post shows how to make a remote monitor, too, if you need the bell to ring beyond the range of BLE.

A fun, simple, and useful project. Of course, the cool doorbells now have video. Just be careful not to get carried away.

Toner Transfer, But Not For PCBs

January 9, 2025 by 16 Comments

It is old news that you can print PCB artwork on glossy paper and use a clothes iron to transfer the toner to a copper board, which will resist etchant. But [Squalius] shows us how to do a similar trick with 3D prints in a recent video, which you can see below.

The example used is a QR code, although you can use anything you can print in a mirror image. Of course, heat from a clothes iron isn’t going to be compatible with your 3D-printed plastic. The trick is to use some acrylic medium on the part, place the print face down, and apply more medium to the back of the paper.

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Writing A RISC-V OS From Scratch

January 9, 2025 by 15 Comments

If you read Japanese, you might have seen the book “Design and Implementation of Microkernels” by [Seiya Nuda]. An appendix covers how to write your own operating system for RISC-V in about 1,000 lines of code. Don’t speak Japanese? An English version is available free on the Web and on GitHub.

The author points out that the original Linux kernel wasn’t much bigger (about 8,500 lines). The OS allows for paging, multitasking, a file system, and exception handling. It doesn’t implement interrupt handling, timers, inter-process communication, or handling of multiple processors. But that leaves you with something to do!

The online book covers everything from booting using OpenSBI to building a command line shell. Honestly, we’d have been happier with some interrupt scheme and any sort of crude way to communicate and synchronize across processes, but the 1,000 line limit is draconian.

Since the project uses QEMU as an emulation layer, you don’t even need any special hardware to get started. Truthfully, you probably won’t want to use this for a production project, but for getting a detailed understanding of operating systems or RISC-V programming, it is well worth a look.

If you want something more production-ready, you have choices. Or, stop using an OS at all.