radar

109 Articles

The Device That Won WW2: A History Of The Cavity Magnetron

August 28, 2023 by 55 Comments

[Curious Droid] is back with a history lesson on one of the most important inventions of the 20th century: The cavity magnetron. Forged in the fighting of World War II, the cavity magnetron was the heart of radar signals used to identify attacking German forces.

The magnetron itself was truly an international effort, with scientists from many countries providing scientific advances. The real breakthrough came with the work of  [John Randall] and [Harry Boot], who produced the first working prototype of a cavity magnetron. The device was different than the patented klystron, or even earlier magnetron designs. The cavity magnetron uses physical cavities and a magnetic field to create microwave energy.  The frequency is determined by the size and shape of the cavities.

While the cavity magnetron had been proven to work, England was strapped by the war effort and did not have the resources to continue the work. [Henry Tizzard] brought the last prototype to the USA where it was described as “the most valuable cargo ever brought to our shores”. The cavity magnetron went on to be used throughout the war in RADAR systems both air and sea.

Today, many military RADAR systems use klystrons or traveling wave tube amplifiers due to requirements for accurate frequency pulses.  But the cavity magnetron still can be found in general and commercial aviation RADAR systems, as well as the microwave ovens we all know and love.

Check the video out after the break.

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Doppler Speed Sensor Puts FFT And AGC To Work

August 24, 2023 by 6 Comments

Some people hate to revisit projects that are done and dusted. We get that; it’s a little like reading a book you’ve already read when there are so many others to choose from. But rereading a book sometimes reveals subtle nuances you missed the first time around, and revisiting projects can be much the same, as with this new and improved Doppler radar speed sensor.

We seem to have been remiss in writing up [Limpkin]’s last go-around with the CDM324 microwave module, a 24-GHz transceiver that you can pick up on the cheap from the usual sources, but we’ve featured this handy little module in plenty of other projects. [Limpkin]’s current project uses the same module to create a Doppler speed sensor, but with a little more sophistication all around. Whereas the original used a simple comparator to output a square wave that’s proportional to the Doppler shift and displayed the speed on a simple terminal session, version two takes a different tack.

First, [Limpkin] opted to implement the whole sensor in hardware. The front end is quite different — an op-amp with 84 dB of gain followed by an automatic gain control (AGC) stage built from a MAX9814 microphone preamp. Extraction of the speed from the module output is left to an STM32F301 running an FFT algorithm on the signal coming out of the analog circuit, which essentially picks out the biggest peak in the spectrum and calculates the Doppler shift from that, displaying the results on an LCD display.

Of course, as a [Limpkin] project, there’s a lot more to it than just that. The write-up is very detailed, going down a few enjoyable rabbit holes like characterizing the amplification chain and diving into the details of Johnson-Nyquist noise to chase down stray oscillations. There’s some great stuff here, and it’s well worth a deep read; there’s also the video below that lets you see (and hear) what’s going on.

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Presence Sensor Locks Computer When You Step Away

July 2, 2023 by 14 Comments

Having a computer that locks its screen after a few minutes of inactivity is always a good idea from a security standpoint, especially in offices where there is a lot of foot traffic. Even the five- or ten-minute activity timers that are set on most workstations aren’t really perfect solutions. While ideally in these situations we’d all be locking our screens manually when we get up, that doesn’t always happen. The only way to guarantee that this problem is solved is to use something like this automatic workstation locker.

The project is based around the LD2410 presence sensor — a small 24 GHz radar module featuring onboard signal processing which simplifies the detection of objects and motion. [Enzo] paired one of these modules with a Seeed Studio XIAO nRF52840 development board to listen to the radar module and send the screen lock keyboard shortcut to the computer when it detects that the user has walked away from the machine. The only thing that [Enzo] wants to add is a blinking LED to let the user know when the device is about to timeout so that it doesn’t accidentally lock the machine when not needed.

One of the parts of this build that is a little bit glossed over is the fact that plenty of microcontroller platforms can send keystrokes to a computer even if they’re not themselves a USB keyboard. Even the Arduino Uno can do this, so by now this feature is fairly platform-agnostic. Still, you can use this to your advantage if you have the opposite problem from [Enzo] and need your computer to stay logged in no matter what.

Using Sonar To Measure Traffic Speeds

June 19, 2023 by 21 Comments

One of the most common ways of measuring the speed of a vehicle is by using radar, which typically involves generating radio waves, directing them at a moving vehicle, and measuring the various ways that they return to the device. This is a tried-and-true method, but can be expensive and technically complex. [GeeDub] wanted an easier way of measuring vehicles passing by his home, so he switched to using sonar instead to measure speeds based on the sounds the cars generate themselves.

The method he is using is similar to passive sonar in submarines, which can locate objects underwater based on the sounds they produce. After a false start attempting to measure Doppler shift, he switched to time correlation using two microphones, essentially using stereo audio input to detect subtle differences in arrival times of various sounds to detect the positions of passing vehicles. Doing this fast enough and extrapolating the data gathered, speed information can be calculated. For the data gathering and calculation, [GeeDub] is using a Raspberry Pi to help keep costs down, and some further configuration of the microphones and their power supplies were also needed to ensure quality audio was gathered.

With the system in place in a window, it detected around 9,000 vehicles over a three-day period. The software generates a normal distribution of vehicle speeds for this time, with the distribution centered on around 35 MPH, slightly above the posted speed limit of 30. As long as there’s a clear line of sight to the road using this system it’s just as effective as some other passive systems we’ve seen to measure vehicle speed. Of course, active speed measurement systems are not out of the realm of possibility if you’re willing to spend a little more.

Retrotechtacular: A Closer Look At The VT Proximity Fuze

June 9, 2023 by 16 Comments

Here at Hackaday, our aim is to bring you only the freshest of hacks, which carries the burden of being Johnny-on-the-spot with our source material. So if something of obvious interest to our readers goes viral, we might just choose to skip covering it ourselves, figuring you all have probably seen it already. But, if we can dig a little deeper and bring extra value over and above what the viral content provides — well then that’s another story.

That’s pretty much the story behind the excellent video recently released by [Real Engineering] about “The Secret Weapon That Changed World War 2.” It concerns the VT series of proximity fuzes — it’s a legitimate alternate spelling of “fuse” if a somewhat archaic one — that were used for artillery shells and spin-stabilized rockets in World War II. The video gives an excellent overview of the development of the VT, which was used primarily in anti-aircraft artillery (AAA). The details about the development of the American VT fuze are excellent, although curiously there’s no mention that British experiments with a radio proximity fuze were part of the goldmine of information brought to America at great risk by the Tizard mission in 1940. While there has been plenty of contention about the exact role the British work played, it’s fair to say that it at least informed the development and fielding of the American VT fuze.

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Neural Network Helps With Radar Pipeline Diagnostics

May 31, 2023 by 3 Comments

Diagnosing pipeline problems is important in industry to avoid costly or dangerous failures from cracked, broken, or damaged pipes. [Kutluhan Aktar] has built an system that uses AI to assist in this difficult task.

The core of the system is a MR60BHA1 60 GHz mmWave radar module, which is most typically used for breathing and heartrate detection. Here, it’s repurposed to detect fluctuating vibrations as a sign that a pipeline may be cracked or damaged. It’s paired with an Arduino Nicla Vision module, with the smart camera able to run a neural network model on the captured radar data to flag potential pipe defects and photograph them. The various modules are assembled on a PCB resembling Dragonite, the Dragon/Flying-type Pokemon.

[Kutluhan] walks us through the whole development process, including the creation of a web interface for the system. Of particular interest is the way the neural network was trained on real defect models that [Kutluhan] built using PVC pipe. We’ve looked at industrial pipelines in detail before, too. Video after the break.

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Real Radar Scope CRT Shows Flights Using ADS-B

April 15, 2023 by 12 Comments

Real-time flight data used to be something that was only available to air traffic controllers, hunched over radar scopes in darkened rooms watching the comings and goings of flights as glowing phosphor traces on their screens. But that was then; now, flight tracking is as simple as pulling up a web page. But where’s the fun in that?

To bring some of that old-school feel to his flight tracking, [Jarrett Cigainero] has been working on this ADS-B scope that uses a real radar CRT. As you can imagine, this project is pretty complex, starting with driving the 5FP7 CRT, a 5″ round-face tube with a long-persistence P7-type phosphor. The tube needs about 7 kV for the anode, which is delivered via a homebrew power supply complete with a custom flyback transformer. There’s also a lot going on with the X-Y deflection amps and beam intensity control.

The software side has a lot going on as well. ADS-B data comes from an SDR dongle using dump1090 running on a Raspberry Pi 3B. The latitude and longitude of each plane within range — about 5 nautical miles — is translated to vector coordinates, and as the “radar” sweeps past the location, a pip lights up on the scope. And no, you’re not seeing things if you see two colors in the video below; as [TubeTime] helpfully explains, P7 is a cascade phosphor that initially emits a bright-blue light with some UV in it, which then charges up a long-persistence green phosphor.

Even though multicolored icons and satellite imagery may be more useful for flight tracking, we really like the simple retro look [Jarrett] has managed to pull off here, not to mention the hackery needed to do it.

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