Building A Functional Aliens Motion Tracker

October 2, 2025 by Lewin Day 6 Comments

Aliens is the second film from the legendary science-fiction series about, well… aliens. Naturally, it featured some compelling future-tech — such as the M314 Motion Tracker. [RobSmithDev] wanted to recreate the device himself, using modern technology to replicate the functionality as closely as possible.

While a lot of cosmetic replicas exist in the world, [Rob] wanted to make the thing work for real. To that end, he grabbed the DreamHAT+ Radar HAT for the Raspberry Pi. It’s a short-range radar module, and thus is useless for equipping your own air force or building surface-to-air weaponry. However, it can detect motion in a range of a few meters or so, using its 60 GHz transmitter and three receivers all baked into the one chip.

[Rob] does a great job of explaining how the radar works, and how he integrated it into a viable handheld motion tracker that works very similarly to the one in the movie. It may not exactly keep you safe from alien predators, but it’s always fun to see a functional prop rather than one that just looks good.

This isn’t the first time we’ve seen somebody try to replicate this particular prop, but the modern electronics used in this build definitely bring it to the next level.

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The DEW Line Remembered

July 16, 2025 by Al Williams 20 Comments

The DEW line was one of three radar early warning systems of the time.

If you grew up in the middle of the Cold War, you probably remember hearing about the Distant Early Warning line between duck-and-cover drills. The United States and Canada built the DEW line radar stations throughout the Arctic to detect potential attacks from the other side of the globe.

MIT’s Lincoln Lab proposed the DEW Line in 1952, and the plan was ambitious. In order to spot bombers crossing over the Arctic circle in time, it required radar twice as powerful as the best radar of the day. It also needed communications systems that were 99 percent reliable, even in the face of terrestrial and solar weather.

In the end, there were 33 stations built from Alaska to Greenland in an astonishing 32 months. Keep in mind that these stations were located in a very inhospitable environment, where temperatures reached down to -60 °F (-51 °C). Operators kept the stations running 24/7 for 36 years, from 1957 to 1993.

System of Systems

The DEW line wasn’t the only radar early-warning system that the US and Canada had in place, only the most ambitious. The Pinetree Line was first activated in 1951. However, its simple radar was prone to jamming and couldn’t pick up things close to the ground. It was also too close to main cities along the border to offer them much protection. Even so, the 33 major stations, along with six smaller stations, did better than expected. Continue reading “The DEW Line Remembered” →

Presence Detection Augments 1930s Home

April 18, 2025 by Bryan Cockfield 18 Comments

It can be jarring to see various sensors, smart switches, cameras, and other technology in a house built in the 1930s, like [Chris]’s was. But he still wanted presence detection so as to not stub any toes in the dark. The result is a sensor that blends in with the home’s aesthetics a bit better than anything you’re likely to find at the Big Box electronics store.

For the presence detection sensors, [Chris] chose to go with 24 GHz mmwave radar modules that, unlike infrared sensors, can detect if a human is in an area even if they are incredibly still. Paired with the diminutive ESP32-S2 Mini, each pair takes up very little real estate on a wall.

Although he doesn’t have a 3D printer to really pare down the size of the enclosure to the maximum, he found pre-made enclosures instead that are fairly inconspicuous on the wall. Another design goal here was to make sure that everything was powered so he wouldn’t have to perpetually change batteries, so a small wire leads from the prototype unit as well.

The radar module and ESP pair are set up with some code to get them running in Home Assistant, which [Chris] has provided on the project’s page. With everything up and running he has a module that can control lights without completely changing the aesthetic or behavior of his home. If you’re still using other presence sensors and are new to millimeter wave radar, take a look at this project for a good guide on getting started with this fairly new technology.

Hacked Ultrasonic Sensors Let You See With Sound

December 6, 2024 by Dan Maloney 13 Comments

If you want to play with radar — and who could blame you — you can pretty easily get your hands on something like the automotive radar sensors used for collision avoidance and lane detection. But the “R” in radar still stands for “Radio,” and RF projects are always fraught, especially at microwave frequencies. What’s the radar enthusiast to do?

While it’s not radar, subbing in ultrasonic sensors is how [Dzl] built this sonar imaging system using a lot of radar principles. Initial experiments centered around the ubiquitous dual-transducer ultrasonic modules used in all sorts of ranging and detection project, with some slight modifications to tap into the received audio signal rather than just using the digital output of the sensor. An ESP32 and a 24-bit ADC were used to capture the echo signal, and a series of filters were implemented in code to clean up the audio and quantify the returns. [Dzl] also added a downsampling routine to bring the transmitted pings and resultant echoes down in the human-audible range; they sound more like honks than pings, but it’s still pretty cool.

To make the simple range sensor more radar-like, [Dzl] needed to narrow the beamwidth of the sensor and make the whole thing steerable. That required a switch to an automotive backup sensor, which uses a single transducer, and a 3D printed parabolic dish reflector that looks very much like a satellite TV dish. With this assembly stuck on a stepper motor to swivel it back and forth, [Dzl] was able to get pretty good images showing clear reflections of objects in the lab.

If you want to start seeing with sound, [Dzl]’s write-up has all the details you’ll need. If real radar is still your thing, though, we’ve got something for that too.

Thanks to [Vanessa] for the tip.

Bogey Six O’clock!: The AN/APS-13 Tail Warning Radar

October 31, 2024 by Danie Conradie 20 Comments

Although we think of air-to-air radar as a relatively modern invention, it first made its appearance in WWII. Some late war fighters featured the AN/APS-13 Tail Warning Radar to alert the pilot when an enemy fighter was on his tail. In [WWII US Bombers]’ fascinating video we get a deep dive into this fascinating piece of tech that likely saved many allied pilots’ lives.

Fitted to aircraft like the P-51 Mustang and P-47 Thunderbolt, the AN/APS-13 warns the pilot with a light or bell if the aircraft comes within 800 yards from his rear. The system consisted of a 3-element Yagi antenna on the vertical stabilizer, a 410 Mhz transceiver in the fuselage, and a simple control panel with a warning light and bell in the cockpit.

In a dogfight, this allows the pilot to focus on what’s in front of him, as well as helping him determine if he has gotten rid of a pursuer. Since it could not identify the source of the reflection, it would also trigger on friendly aircraft, jettisoned wing tanks, passing flak, and the ground. This last part ended up being useful for safely descending through low-altitude clouds.

This little side effect turned out to have very significant consequences. The nuclear bombs used on Hiroshima and Nagasaki each carried four radar altimeters derived from the AN/APS-13 system.

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Fundamentals Of FMCW Radar Help You Understand Your Car’s Point Of View

October 19, 2024 by Dan Maloney 3 Comments

Pretty much every modern car has some driver assistance feature, such as lane departure and blind-spot warnings, or adaptive cruise control. They’re all pretty cool, and they all depend on the car knowing where it is in space relative to other vehicles, obstacles, and even pedestrians. And they all have another thing in common: tiny radar sensors sprinkled around the car. But how in the world do they work?

If you’ve pondered that question, perhaps after nearly avoiding rear-ending another car, you’ll want to check out [Marshall Bruner]’s excellent series on the fundamentals of FMCW radar. The linked videos below are the first two installments. The first covers the basic concepts of frequency-modulated continuous wave systems, including the advantages they offer over pulsed radar systems. These advantages make them a great choice for compact sensors for the often chaotic automotive environment, as well as tasks like presence sensing and factory automation. The take-home for us was the steep penalty in terms of average output power on traditional pulsed radar systems thanks to the brief time the radar is transmitting. FMCW radars, which transmit and receive simultaneously, don’t suffer from this problem and can therefore be much more compact.

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Amateur Astronomer Images Spy Satellite

September 20, 2024 by Bryan Cockfield 14 Comments

As anyone who’s looked at the sky just before dawn or right after dusk can confirm, for the last seventy years or so there have been all kinds of artificial satellites floating around in low-Earth orbit that are visible to the naked eye. Perhaps the most famous in the last few decades is the International Space Station, but there are all kinds of others up there from amateur radio satellites, the Starlink constellation, satellite TV, and, of course, various spy satellites from a few of the world’s governments. [Felix] seems to have found one and his images of it can be found here.

[Felix] has been taking pictures of the night sky for a while now, including many different satellites. While plenty of satellites publish their paths to enable use, spy satellites aren’t generally public record but are still able to be located nonetheless. He uses a large Dobsonian telescope to resolve the images of several different satellites speculated to be spy satellites, with at least one hosting a synthetic aperture radar (SAR) system. His images are good enough to deduce the size and shape of the antennas used, as well as the size of the solar panels on board.

As far as being concerned about the ramifications of imaging top-secret technology, [Felix] is not too concerned. He states that it’s likely that most rival governments would be able to observe these satellites with much more powerful telescopes that he has, so nothing he has published so far is likely to be a surprise to anyone. Besides, these aren’t exactly hidden away, either; they’re up in the sky for anyone to see. If you want to take a shot at that yourself you can get a Dobsonian-like telescope mostly from parts at Ikea, and use a bit of off-the-shelf electronics to point them at just the right position too.