A 1960s PLC Gives Up Its Secrets

February 15, 2024 by Jenny List 7 Comments

When it comes to process automation, the go-to part in most industrial settings is a Programmable Logic Controller, or PLC. These specialized computers will have a modern microcontroller running the show, but surprisingly the way they are programmed still has echoes of a time before electronic PLCs when such control would have been electromechanical.

[Thomas Scherrer] has an interesting design to tear down, it’s a Siemens electromechanical motor controller from the early 1960s. It’s not quite the huge banks of relays which would have made a fully-blown PLC back in those times, but it’s a half-way house with some simple programming capability in the form of several channels of adjustable time delay.

We’re partly sad to see this unit being subjected to a destructive teardown, but nevertheless it’s interesting to see all those very period components. The current sensor has a mechanism similar to a moving coil meter, and the four-channel timer is a mechanical sequencer with four adjustable cam-driven switches. We’re not sure we would be cracking open selenium rectifiers with such nonchalance though.

These units were built to a very high quality indeed, and though it’s obvious this one comes from a decommissioned installation it’s not beyond possibility to think there might be some of them still doing their job over six decades after manufacture. Have any of you seen one of these or something like it in operation recently? Let us know in the comments. Meanwhile the video is below the break.

Continue reading “A 1960s PLC Gives Up Its Secrets” →

In Praise Of Old Meters

January 12, 2024 by Al Williams 54 Comments

We are spoiled with multimeters today. Even the cheapest meter you will get these days is almost surely digital with a tremendous input impedance. But a few decades ago, meters were almost always analog affairs. To make a precise measurement, you needed a mirror under the meter to ensure you read the needle correctly. Moreover, a common meter wouldn’t have that high of an input impedance. If you spent more, you could get a VTVM and, later, one that used FETs to provide high input impedance. [Peter AA2VG] just picked up a vintage Micronta FET volt-ohm meter to join some of the other new and old meters in his shack. You can check it out in the video below.

[Peter] already has a Simpson and a more modern Fluke meter. The Simpson, however, doesn’t have a tube or FET amplifier. The Fluke is nice, but there is something about the needle on an analog meter. If you aren’t old enough to remember, the Micronta brand was a Radio Shack label.

Continue reading “In Praise Of Old Meters” →

Half Power Bank, Half Spot Welder

January 8, 2024 by Jenny List 13 Comments

There was a time when every gizmo on AliExpress also had a big white LED so it could also work as a flashlight, but maybe the power bank is the new flashlight. [Aaron Christophel] has a battery spot welder that costs a not unreasonable 30 euros and can also be used as a novelty power bank. He subjects it to a test and teardown in the video below the break.

First of all, he conducts a few weld tests, and we have to say it seems capable of some reasonable results if its parameters are correctly adjusted. Then the end comes off the extruded aluminium case, and the guts of the device are slid out for a teardown.

The power comes from a pair of Li-Po pouch cells, while on the board, there’s an STM32 clone providing the timing for a set of MOSFETs that do the heavy lifting. There’s a colour display for tweaking the settings. Alongside all this, there’s also a small chip for that power bank functionality. Charging is via USB-C, though, of course, it’s not really proper USB-C but a USB-C socket that expects 5 volts. This is a disappointing trend in cheap electronics that sullys the promise of USB-C.

It seems this spot welder is capable of doing the job, which is pleasing after our previous disappointing look at battery welders.

Continue reading “Half Power Bank, Half Spot Welder” →

Teardown Of Two Russian Missile Sensors

January 5, 2024 by Maya Posch 22 Comments

Recently [Michel] received two packages from Ukraine containing some salvaged Russian electronics that once belonged to (presumably) a 9K38 Igla, Vympel R-27 or similar infrared homing missile, as well as a Fiber Optic Gyroscope (FOG) from an unknown missile, though possibly from the Tornado family of MRLSes. The latter uses the Sagnac effect to detect the phase shift between two laser beams being injected into the same fiber when the fiber, and thus the device, are rotating. The advantage of such a gyroscope is that it is effectively solid-state, requiring only some optical components, amplifier stage and as shown here an Altera Cyclone II FPGA to integrate the results.

The 16-channel linear infrared array sensor is more basic, with a matching amplification channel for each optical receiver element, which are fed into a multiplexer IC in a rather remarkable looking ceramic-gold packaged DIP format, with what looks like a 2004 date code (‘0424’). Although both are rather damaged, [Michel] figures that he might be able to restore the FOG to working condition, assuming no crucial and irreplaceable parts are missing. As useful as FOGs are in missiles, they also have countless uses outside of military applications.

Continue reading “Teardown Of Two Russian Missile Sensors” →

Teardown Of FGM-148 Javelin Missile’s Guidance Computer

December 21, 2023 by Maya Posch 45 Comments

You know it’s a good teardown when [Michel] starts off by saying to not ask him where exactly he got the guidance section of an FGM-148 Javelin from. This shoulder-launched anti-tank guided missile (ATGM) is a true marvel of engineering that has shown its chops during recent world events. As a fire-and-forget type guided missile it is designed to use the internal IR tracker to maintain a constant lock on the target, using its guidance system to stay exactly on track.

FGM-148 Javelin schematic overview. (Source: U.S. Army, FM 3-22.37)

Initially designed in 1989 and introduced into service in 1996, it has all the ceramic-and-gold styling which one would expect from a military avionics package from the era. Tasked with processing the information from the IR sensor, and continuously adjusting the fins to keep it on course, the two sandwiched, 3 mm thick PCBs that form the main section of the guidance computer are complemented by what looks like a milled aluminium section which holds a sensor and a number of opamps, all retained within the carbon-fiber shell of the missile.

In the video [Michel] looks at the main components, finding datasheets for many commercially available parts, with the date codes on the parts confirming that it’s a late 80s to early 90s version, using presumably a TMS34010 as the main CPU on the DSP board for its additional graphics-related instructions. Even though current production FGM-148s are likely to use far more modern parts, this is a fun look at what was high-end military gear in the late 1980s and early 1990s.

Continue reading “Teardown Of FGM-148 Javelin Missile’s Guidance Computer” →

Up Close And Personal With A MEMS Microphone

December 20, 2023 by Dan Maloney 14 Comments

If you’ve ever wondered what lies beneath the barely visible hole in the can of a MEMS microphone, you’re in luck, because [Zach Tong] has a $10 pair of earbuds to sacrifice for the cause and an electron microscope.

For the uninitiated, MEMS stands for microelectromechanical systems, the tiny silicon machines that power some of the more miraculous functions of smartphones and other modern electronics. The most familiar MEMS device might be the accelerometer that gives your phone a sense of where it is in space; [Zach] has a deep dive into MEMS accelerometers that we covered a while back.

MEMS microphones seem a little bit easier to understand mechanically, since all they have to do is change vibrations in air into an electrical signal. The microphone that [Zach] tore down for this video is ridiculously small; the SMD device is only about 3 mm long, with the MEMS chip under the can a fraction of a millimeter on a side. After some overall views with the optical microscope, [Zach] opened the can and put the guts under his scanning electron microscope. The SEM shots are pretty amazing, revealing a dimpled silicon diaphragm over a second layer with holes etched right through it. The dimples on the diaphragm nest into the holes, forming an air-dielectric capacitor whose capacitance varies as sound waves vibrate the diaphragm.

The most visually interesting feature, though, might be the deep cavity lying behind the two upper surfaces. The cavity, which [Zach] says bears evidence of having been etched by the deep reactive ion etching method, has cool-looking corrugations in its walls. The enormity of the cavity relative to the thin layers covering it suggests it’s a resonating cavity for the sound waves.

Thanks to [Zach] for this in-depth look at a device that’s amazingly complex yet remarkably simple.

Continue reading “Up Close And Personal With A MEMS Microphone” →

It’s An Audio Distortion Analyzer, Just Not The One You Were Hoping For

December 19, 2023 by Jenny List 7 Comments

An audio distortion analyzer is a specialist piece of analogue test equipment that usually costs a lot of money and can be hard to track down on the second hand market. Finding one is a moment of luck for the average engineer then, but [Thomas Scherrer OZ2CPU]’s discovery isn’t quite what he might have hoped for. Nonetheless, his Bang and Olufsen K3 Distortion meter DM1 from 1979 is still an interesting and high quality piece of test equipment, and the video below the break makes for a worthwhile watch.

Bang and Olufsen are best known for high-end design Hi-Fi units, thus it’s a surprise to find that in the past they also manufactured test equipment. This distortion meter isn’t a general purpose one, instead it’s designed to measure tape recorders in particular, and it uses an elegant technique. Instead of injecting a sine wave and removing it from what comes out in order to measure the products of the distortion, it records a 333 Hz sine wave onto a tape, then measures the strength of its 3rd harmonic at 1 kHz as an indication of distortion. It’s a working distortion meter made with clever analogue circuitry for a fraction of the cost of the more conventional models that HP would have sold you at the same time, even if it doesn’t give the same THD figure you might have been looking for.

If distortion interests you, it’s a subject we’ve looked at in the past.

Continue reading “It’s An Audio Distortion Analyzer, Just Not The One You Were Hoping For” →