What’s In A Wattmeter?

May 13, 2022 by Al Williams 2 Comments

The idea behind watts seems deceptively simple. By definition, a watt is the amount of work done when one ampere of current flows between a potential of one volt. If you think about it, a watt is basically how much work is done by a 1V source across a 1Ω resistor. That’s easy to say, but how do you measure it in the real world? [DiodeGoneWild] has the answer in a recent video where he tears a few wattmeters open.

There are plenty of practical concerns. With AC, for example, the phase of the components matters. The first 11 minutes of the video are somewhat of a theory review, but then the cat intervenes and we get to see some actual hardware.

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Absolute Encoder Teardown

May 13, 2022 by Al Williams 22 Comments

According to [Lee Teschler], the classic representation of encoders showing code rings is out of date. His post says that most industrial absolute encoders use a special magnetic sensor known as a Wiegand wire to control costs. To demonstrate he does a teardown of an encoder made by Nidec Avtron Automation, and if you’ve ever wondered what’s inside something like this, you enjoy the post.

This is a large industrial unit and when you open it up, you’ll get a surprise. Most of the inside is empty! There is a very small encoder inside. The main body protects the inside and holds the large bearings. The real encoder looks more like a toy car motor than anything else.

The inner can is nearly empty, too. But it does have the part we are interested in. There’s a Melexis Hall effect sensor The Weigand wire is a special magnetic wire with an outer sheath that is resistant to having its magnetic field reversed and an inner core that isn’t. Until an applied magnetic field reaches a certain strength, the wire will stay magnetized in one direction. When the field crosses the threshold, the entire wire changes magnetic polarity rapidly. The effect is independent of the rate of change of the applied magnetic field.

In other words, like old core memory, the wire has strong magnetic hysteresis. Between pulses from the Weigand wire and information from the Hall effect sensor, you can accurately determine the position of the shaft.

It is always amazing to us how many modern pieces of gear are now mostly empty with the size of the device being driven by physical constraints and not the electronics within.

Coin Acceptors Are Higher-Tech Than You Think

April 10, 2022 by Al Williams 16 Comments

Coin-operated machines have a longer history than you might think. Ancient temples used them to dispense, for example, holy water to the faithful in return for their coins. Old payphones rang a bell when you inserted a coin so the operator knew you paid. Old pinball machines had a wire to catch things with holes in the middle so you couldn’t play with washers. But like everything else, coin acceptors have advanced quite a bit. [Electronoobs] shows a unit that can accept coins from different countries and it is surprisingly complex inside. He used what he learned from the teardown to build his own Arduino-based version.

For scale, there is the obligatory banana. Inside the box there are several induction coils and some photo electronics. In particular, there are two optical sensors that watch the coin roll down a ramp. This produces two pulses. The width of the pulse indicates the diameter of the coin, and the time between the pulses tells its speed.

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A Close Look At A Little Known 8-bit Computer

April 8, 2022 by Al Williams 47 Comments

If you read about the history of personal computing, you hear a few familiar names like Microsoft, Apple, and even Commodore. But there were a host of companies that were well known and well regarded back then that are all but forgotten today. Godbout computing, Ohio Scientific, and Southwest Technical Products (SWTP). SWTP is probably best remembered for having a relatively cheap printer and “TV typewriter”, but they also made a 6800-based computer and [Adrian] takes us inside of one.

The 6800 was Motorola’s entry into the microprocessor fray, competing with the Intel 8080. The computer came out scant months after the introduction of the famous Altair 8800. Although the Altair is often credited as being the first hobbyist-grade computer, there were a few earlier ones based on the 8008, but the Altair was the first to be successful.

The SWTP was notable for its day for its blank appearance. Most computers in those days had lots of switches and lights. The SWTP has a blank front with only a power switch and a reset button. A ROM monitor let you use the machine with a terminal. For about the same price as a bare-bones Altair that had no interfaces or memory, you could pick one of these up with most of the extras you would need. The memory was only 2K, but that was 2K more than you got with an Altair at that price point.

The $450 sounds fairly cheap, but in the early 70s, that was a lot of lawns to mow. Of course, while you’d need to add memory to the Altair, you’d have to add some kind of terminal to the SWTP. However, you’d wind up with something more usable but the total bill was probably going to approach $1,000 to get a working system.

Inside the box were some old-fashioned-looking PC boards and connectors that will look familiar to anyone who has been inside 1970s gear. Will it work? We don’t know yet, but we hope it does. [Adrian] promises that will be in the next video.

It is amazing how far we’ve come in less than 50 years. A postage-stamp sized $10 computer now has enough speed and memory to emulate a bunch of these old machines all at once. The SWTP has been on our pages before. A lot of these old machines and companies are all but forgotten, but not by us!

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Detailed Big Screen Multimeter Review

April 4, 2022 by Al Williams 5 Comments

It seems like large-screen cheap meters are really catching on. [TheHWcave] does a very detailed review of a KAIWEETS KM601, which is exactly the same as a few dozen other Chinese brands you can get from the usual sources. You can see the review in the video below.

If we learned nothing else from this video, we did learn that you can identify unmarked fuses with a scale. The fuses inside were not marked, so he wanted to know if they appeared to be the right values. We would have been tempted to just blow them under controlled conditions, but we get he didn’t want to destroy the stock fuses until after testing.

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Is Your Device Actually USB 3.0, Or Is The Connector Just Blue?

April 3, 2022 by Donald Papp 66 Comments

Discount (or even grey market) electronics can be economical ways to get a job done, but one usually pays in other ways. [Majenko] ran into this when a need to capture some HDMI video output ended up with rather less than was expected.

Faced with two similar choices of discount HDMI capture device, [Majenko] opted for the fancier-looking USB 3.0 version over the cheaper USB 2.0 version, reasoning that the higher bandwidth available to a USB 3.0 version would avoiding the kind of compression necessary to shove high resolution HDMI video over a more limited USB 2.0 connection.

The device worked fine, but [Majenko] quickly noticed compression artifacts, and interrogating the “USB 3.0” device with lsusb -t revealed it was not running at the expected speeds. A peek at the connector itself revealed a sad truth: the device wasn’t USB 3.0 at all — it didn’t even have the right number of pins!

A normal USB 3.0 connector is blue inside, and has both sets of pins for backward compatibility (five in the rear, four in the front) like the one shown here.

A USB 3.0 connection requires five conductors, and the connectors are blue in color. Backward compatibility is typically provided by including four additional conductors, as shown in the image here. The connector on [Majenko]’s “USB 3.0” HDMI capture device clearly shows it is not USB 3.0, it’s just colored blue.

Most of us are willing to deal with the occasional glitch or dud in exchange for low prices, but when something isn’t (and never could be) what it is sold as, that’s something else. [Majenko] certainly knows that as well as anyone, having picked apart a defective power bank module to uncover a pretty serious flaw.

Talking To A Texas Instruments Calculator

March 17, 2022 by Bryan Cockfield 22 Comments

Texas Instruments is a world-class semiconductors company, but unfortunately what they are best known for among the general public is dated consumer-grade calculators thanks to entrenched standardized testing. These testing standards are so entrenched, in fact, that TI has not had to update the hardware in these calculators since the early 90s. They still run their code on a Z80 microcontroller, but [Ben Heck] found himself in possession of one which has a modern ARM coprocessor in it and thus can run Python.

While he’s not sure exactly what implementation of Python the calculator is running, he did tear it apart to try and figure out as much as he could about what this machine is doing. The immediately noticeable difference is the ARM coprocessor that is not present in other graphing calculators. After some investigation of test points, [Ben] found that the Z80 and ARM chips are communicating with each other over twin serial lines using a very “janky” interface. Jankiness aside, eventually [Ben] was able to wire up a port to the side of the calculator which lets him use his computer to send Python commands to the device when it is in its Python programming mode.

While there are probably limited use cases for 1980s calculators to run Python programs, we can at least commend TI for attempting to modernize within its self-built standardized testing prison. Perhaps this is the starting point for someone else to figure out something more useful to put these machines to work with beyond the classroom too. We’ve already seen some TI-84s that have been modified to connect to the Internet, for example.

Thanks to [Nikša] for the tip!

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