Practical Sensors: The Many Ways We Measure Heat Electronically

February 19, 2021 by Al Williams 24 Comments

Measuring temperature turns out to be a fundamental function for a huge number of devices. You furnace’s programmable thermostat and digital clocks are obvious examples. If you just needed to know if a certain temperature is exceeded, you could use a bimetalic coil and a microswitch (or a mercury switch as was the method with old thermostats). But these days we want precision over a range of readings, so there are thermocouples that generate a small voltage, RTDs that change resistance with temperature, thermistors that also change resistance with temperature, infrared sensors, and vibrating wire sensors. The bandgap voltage of a semiconductor junction varies with temperature and that’s predictable and measurable, too. There are probably other methods too, some of which are probably pretty creative.

Bimetalic coil by [Hustvede], CC-BY-SA 3.0.

You can often think of creative ways to do any measurement. There’s an old joke about the smart-alec student in physics class. The question was how do you find the height of a building using a barometer. One answer was to drop the barometer from the top of the building and time how long it takes to hit the ground. Another answer — doubtlessly an engineering student — wanted to find the building engineer and offer to give them the barometer in exchange for the height of the building. By the same token, you could find the temperature by monitoring a standard thermometer with a camera or even a level sensor which is a topic for another post.

The point is, there are plenty of ways to measure anything, but in every case, you are converting what you want to know (temperature) into something you know how to measure like voltage, current, or physical position. Let’s take a look at how some of the most interesting temperature sensors accomplish this.

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Test Equipment, Shim Washers, And A 30 Year Old Space Telescope

April 29, 2020 by Al Williams 38 Comments

This year marks the 30th anniversary of the Hubble Space Telescope. When you see all the great pictures today, it is hard to remember that when it first launched, it was nearly a failure, taking fuzzy pictures. The story of how that problem was fixed while the telescope was whizzing through space is a good one. But there’s another story: how did a $1.5 billion satellite get launched with defective optics? After all, we know space hardware gets tested and retested and, typically, little expense is spared to make sure once a satellite is in orbit, it will work well for a long time.

The problem was with a mirror. You might think mirrors are pretty simple, but it turns out there’s a lot to know about mirrors. For astronomy, you need a first surface mirror which is different from your bathroom mirror which almost certainly reflects off the back of the glass. In addition, the mirrors need a very precise curve to focus light.

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Teardown: VTech Whiz Kid Luggable Computer

April 27, 2020 by Tom Nardi 47 Comments

Back in the early 1980s, hotshot business types on the go would have used what were referred to at the time as portable computers from companies like Osborne or Kaypro. Due to the technical limitations of the era these so-called “luggables” were only slightly smaller and lighter than contemporary desktop computers, but they had integrated displays and keyboards so they were a bit easier to move around. A few years later the first generation of laptops would hit the market, and the portables predictably fell out of favor. Today they’re relatively rare collectors items; a largely forgotten first step in the steady march towards true mobile computing.

Which makes the 1984 edition of VTech’s “Whiz Kid” educational computer an especially unique specimen. The company’s later entries into the series of popular electronic toys would adopt (with some variations) the standard laptop form factor, but this version has the distinction of being what might be the most authentic luggable computer ever made for children. When this toy was being designed it would have been a reflection of the cutting edge in computer technology, but today, it’s a fascinating reminder that the latest-and-greatest doesn’t always stick around for very long.

The classic luggable hallmarks are all here. The flip down keyboard, the small and strangely offset display, there’s even lugs on the side to attach an included strap so the youngster can sling it over their shoulder. On the other hand, the fact that it’s just a toy allowed for some advantages over the real thing: it can actually run on battery power, and is quite lightweight relative to its size.

When we last took a peek inside one of VTech’s offerings, we found a surprisingly powerful Z80 machine that was more than deserving of its PreComputer moniker. But that BASIC-compatible design hailed from the late 80s, and was specifically marketed as a trainer for the next generation of computer owners. Will the 1984 Whiz Kid prove to have a similar relationship to its adult counterparts, or does the resemblance only go skin deep? Let’s find out.

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Analyzing CNC Tool Chatter With Audacity

January 16, 2020 by Dan Maloney 32 Comments

When you’re operating a machine that’s powerful enough to tear a solid metal block to shards, it pays to be attentive to details. The angular momentum of the spindle of a modern CNC machine can be trouble if it gets unleashed the wrong way, which is why generations of machinists have developed an ear for the telltale sign of impending doom: chatter.

To help develop that ear, [Zachary Tong] did a spectral analysis of the sounds of his new CNC machine during its “first chip” outing. The benchtop machine is no slouch – an Avid Pro 2436 with a 3 hp S30C tool-changing spindle. But like any benchtop machine, it lacks the sheer mass needed to reduce vibration, and tool chatter can be a problem.

The analysis begins at about the 5:13 mark in the video below, where [Zach] fed the soundtrack of his video into Audacity. Switching from waveform to spectrogram mode, he was able to identify a strong signal at about 5,000 Hz, corresponding to the spindle coming up to speed. The white noise of the mist cooling system was clearly visible too, as were harmonic vibrations up and down the spectrum. Most interesting, though, was the slight dip in frequency during the cut, indicating loading on the spindle. [Zach] then analyzed the data from the cut in the frequency domain and found the expected spindle harmonics, as well the harmonics from the three flutes on the tool. Mixed in among these were spikes indicating chatter – nothing major, but still enough to measure.

Audacity has turned out to be an incredibly useful tool with a broad range of applications. Whether it be finding bats, dumping ROMs, detecting lightning strikes, or cloning remote controls, Audacity is often the hacker’s tool of choice.

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Hide Silent, Hide Deep: Submarine Tracking Technologies Of The Cold War

January 10, 2020 by Al Williams 48 Comments

All through the cold war, there was a high-stakes game of cat and mouse in play. Nuclear powers like the United States and the Soviet Union would hide submarines armed with nuclear missiles underwater. The other side would try to know where they were so they could be targeted in the event of war. The common wisdom was that the United States had many high tech gadgets to help track enemy submarines, but that the Soviet Union was way behind in this area. This was proven false when a Soviet Victor-class boat followed a US missile submarine for six days. Now, a recently declassified CIA report shows how the Soviets didn’t use sonar at all but developed their own technology.

There is something fascinating about submarines. Like an old sailing ship, submarines are often out of touch with their command bases and the captain is the final authority. Like a space ship, the submarine has to survive in an inimical environment. I guess in all three cases, the crew doesn’t just use technology, they depend on it.

Although the submarine has some non-military uses, there are probably more military subs than any other type. After all, a sub is as close to a cloaking device as any real-life military vehicle has ever had. Before modern technology offered ways to find submarines using sonar or magnetic anomalies, a completely submerged submarine was effectively invisible.

There was a lot of speculation that the Soviet Union lacked sufficient technology to use sonar the way the US did. However, in some cases, they had simply developed different types of detection — many of which the West had discarded as impractical.

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Simple Seismic Sensor Makes Earthquake Detection Personal

October 28, 2019 by Dan Maloney 6 Comments

When an earthquake strikes, it’s usually hard to miss. At least that’s the case with the big ones; the dozens or hundreds of little quakes that go largely unnoticed every day are interesting too, and make sense to track. That’s usually left to the professionals, with racks of sensitive equipment and a far-flung network of seismic sensors. That doesn’t mean you can’t keep track of doings below your feet yourself, with something like this DIY seismograph.

Technically, what [Alex] built is better called a “seismic detector” since it’s not calibrated in any way. It’s just a simple sensor for detecting ground vibrations, whether they be due to passing trucks or The Big One. [Alex] lives in California, wedged between the Hayward, Calaveras, and San Andreas faults in San Jose, so there is plenty of opportunity for testing his device. The business end is a simple pendulum sensor, with a heavy metal bob hanging from a long wire inside a length of plastic pipe. Positioned close to the bob is a copper plate; the bob and the plate form an air-dielectric variable capacitor that controls the frequency of a simple 555 oscillator. The frequency is measured by a PIC microcontroller and sent to a Raspberry Pi, which displays the data on a graph. You can check in on real-time seismic activity in San Jose using the link above, or check out historical quakes, like the 7.1 magnitude Ridgecrest quake in July. [Alex]’s sensor is sensitive enough to pick up recent quakes in Peru, Fiji, and Nevada, and he even has some examples of visualizing the Earth’s core using data from the sensor. How cool is that?

We’ve seen other seismic detectors before, like this piezo-based device, or even one made from toilet parts. We like the simplicity of the capacitive sensor [Alex] used, though.

Hackaday Podcast 035: LED Cubes Taking Over, Ada Vanquishes C Bugs, Rad Monitoring Is Hot, And 3D Printing Goes Full 3D

September 13, 2019 by Mike Szczys No comments

Hackaday Editors Mike Szczys and Elliot Williams get caught up on the most interesting hacks of the past week. On this episode we take a deep dive into radiation-monitor projects, both Geiger tube and scintillator based, as well as LED cube projects that pack pixels onto six PCBs with parts counts reaching into the tens of thousands. In the 3D printing world we want non-planar printing to be the next big thing. Padauk microcontrollers are small, cheap, and do things in really interesting ways if you don’t mind embracing the ecosystem. And what’s the best way to read a water meter with a microcontroller?

Take a look at the links below if you want to follow along, and as always tell us what you think about this episode in the comments!

Take a look at the links below if you want to follow along, and as always, tell us what you think about this episode in the comments!

Direct download (60 MB or so.)