Eye Tube Tests Capacitors

Most component testers require removal of a component to test it. [Mr Carlson] recently restored an old Paco C-25 in-circuit capacitor tester. He does a very complete video tearing it down and showing how it works and why.

The tester uses an eye tube (sometimes called a magic eye tube) as an indicator. A 40 MHz oscillator produces a signal that finds open and shorted capacitors. You can also measure resistance, although you have to wonder how accurate it would be in circuit. If you want to read the original manual, there are a few copies online.

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KIM-1 to COSMAC Elf Conversion — Sort Of

In the mid-1970s, if you had your own computer, you probably built it. If you had a lot of money and considerable building skill, you could make an Altair 8800 for about $395 — better than the $650 to have it built. However, cheaper alternatives were not far behind.

In 1976, Popular Electronics published plans for a computer called the COSMAC Elf which you could build for under $100, and much less if you had a good junk box. The design was simple enough that you could build it on a piece of perf board or using wire wrap. We featured the online archive of the entire Popular Electronics collection, but hit up page 33 of this PDF if you want to jump right to the article that started it all. The COSMAC Elf is a great little machine built around a 40-pin RCA 1802 processor, and for many was the first computer they owned. I lost my original 1802 computer in a storm and my recent rebuild in another completely different kind of storm. But there is a way to reclaim those glory days without starting from scratch.  I’m going to repurpose another retro-computing recreation; the KIM-1.

I’ll admit it, Rewiring a real KIM-1 to take an 1802 CPU would be difficult and unnecessary and that’s not what this article is about. However, I did have a KIM UNO — [Oscar’s] respin of the classic computer using an Arduino mini pro. Looking at the keyboard, it occurred to me that the Arduino could just as easily simulate an 1802 as it could a 6502. Heck, that’s only two digits different, right?

The result is pretty pleasing. A “real” Elf had 8 toggle switches, but there were several variations that did have keypads, so it isn’t that far off. Most Elf computers had 256 bytes of memory (without an upgrade) but the 1802 UNO (as I’m calling it) has 1K. There’s also a host of other features, including a ROM and a monitor for loading and debugging programs that doesn’t require any space in the emulated 1802.

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Simulating Snakes and Ladders for Fun, Not Profit

A great many of you will remember the game of Snakes and Ladders from your youth. It’s a simple game, which one grows to realise involves absolutely no skill – it’s purely the luck of the dice. [Alex Laratro] noticed that without player decisions to effect the outcome, the game was thus a prime candidate for simulation. 

[Alex] wanted to dive into the question of “Who is winning a game of Snakes and Ladders?” at any given point in the gameplay. A common approach would be to state “whoever is in front”, but the ladders might have something to say about that. [Alex] uses Markov analysis to investigate, coming to some interesting conclusions about how the game works, and how this compares to the design of more complex games like Mario Kart and Power Grid.

Overall, it’s a breakdown of a popular game that’s simple enough to really sink your teeth into, but has some incredibly interesting conclusions that are well worth considering for anyone designing their own board games. We love seeing math applied to novel and fun problems – and it can solve important problems, too.

Read Amiga Floppies Using An Arduino

So you spent your youth learning your craft in front of an Amiga 500+, but a quarter century later all you have left is a broken computer and a pile of floppies you can’t read any more. What’s to be done? This was the position [Rob Smith] found himself in, and since some of the commercial solutions to ripping Amiga floppies were rather expensive, he decided to have a go at making his own.

His write-up makes for a fascinating read, as he delves into the physical interface of the PC floppy drive he used, and into the timing required from the Arduino that controlled it. He faced some challenges in getting his code to be fast enough for the task, and goes into some of the optimisation techniques he employed. His code for both Arduino and Windows  is open-source, and can be downloaded from his GitHub repository. Future plans involve supporting the FDI disc format as well as ADF, and adding the ability to write discs.

We’ve shown you a lot of Amigas over the years, but perhaps of most relevance here in our archive are this Raspberry Pi floppy emulator and this floppy autoloader for archiving a disc collection.

Via Hacker News.

DC Motor Whirligig Generates Power

Everyone knows that if you spin the shaft of a DC motor, it will generate power. [Vapsvus] has found a novel way to do this with no direct mechanical connection to the shaft. He simply taped a loop of string around to the motor can. This effectively turns the motor into a whirligig. Flip the motor to give the string a few twists, then pull on the two loops. The string unwinds and then winds back up, just like the toy we all grew up with.

The interesting thing is that the motor generates usable power when being spun like this. [Vapsvus] connected two LEDs to the motor’s leads to show what’s happening. The white LED glows when current travels from positive to negative, and the red LED glows when current travels from negative to positive.

What’s going on under the hood is all about momentum. As the motor can starts to spin, the heavy iron rotor remains still. Power is generated. Eventually, friction and torque from back EMF cause the rotor to spin as well. By the time the rotor is spinning, the motor can is already reversing direction.This generates even more power with current traveling in reverse.

Sure, this isn’t exactly practical, but we’d love to see how far it could be taken. Add a super capacitor, and we bet it would be more efficient than the magnetic shake lights which were popular a few years back.

Whirligigs are usefully little devices. Not only do they keep children entertained, you can use them as centrifuges.

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Charge Your Phone on an Iron Throne

Game of Thrones season 7 is finally here! [Hoecrux] is celebrating by building a GoT inspired cell phone charger. No, this isn’t a 3D print, nor is it vacuum molded. This iron throne was hand made from hundreds of cocktail swords. The frame of the chair is made from medium density fiberboard (MDF). The frame is covered with upholstery foam, then a layer of thin gray foam which forms the surface of the chair.

[Hoecrux] then began the painstaking process of hot gluing 600 cocktail swords to her creation. Each sword had to be modified by cutting off the loop guard. Some of the swords are bent, which was achieved with a heat gun. The completed chair was finished with a coat of black spray paint, followed by dry brushing with acrylic silver paint.

This particular iron throne charger is built for an android phone. [Hoecrux] embedded a micro USB cable in the base of the seat. If you’re of the iOS persuasion, you can substitute a lightning cable.

Check out the video after the link, and while you’re at it, get a look at this beach ready solar charger setup.

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Old Intercom Gets Googled with Raspberry Pi and AIY Hat

Old Radio Shack intercom; brand new Google Voice interface for a Raspberry Pi. One of these things is not like the other, but they ended up together in this retro-look Google Voice interface, and the results are pretty slick.

The recipient of the Google hive-mind transplant was one of three wireless FM intercoms [MisterM] scored for a measly £4. Looking much as they did when they were the must-have office tool or home accessory for your modern mid-80s lifestyle, the intercom case was the perfect host for the Pi and the Google AIY hat. Only the case was used — not even the original speaker made it into the finished product. The case got a good scrubbing, a fresh coat of paint to perk up the gone-green plastic, and an accent strip of Google’s logo colors over the now-deprecated station selector switch. [MisterM] provided a white LED behind the speaker grille for subtle feedback. A tap of the original talk bar gets Google’s attention for answers to quick questions, and integration into the family’s existing home automation platform turns the lights on and off. See it in action after the break.

[MisterM] was lucky enough to score an AIY hat for free, and as far as we know they’re still hard to come by. If you’re itching to try out the board, fear not — turns out you can roll your own.

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