Inside A 1940’s Spy Radio

The RCA CR-88 was a radio receiver made to work in top-secret government eavesdropping stations. As you might expect, these radios are top-of-the-line, performance-wise, at least when they are working correctly. [Mr. Carlson] has one on his bench, and we get to watch the show on his recent video that you can see below.

Interestingly, [Mr. Carlson] uses some Sherlock Holmes-like deductive reasoning to guess some things about the radio’s secret history. The radio’s design is decidedly heavy-duty, with a giant power transformer and many tubes, IF transformers, and large filter capacitors.

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A Single-Resistor Radio Transmitter, Thanks To The Power Of Noise

One of the great things about the Hackaday community is how quickly you find out what you don’t know. That’s not a bad thing, of course; after all, everyone is here to get smarter, right? So let’s work together to get our heads around this paper (PDF) by [Zerina Kapetanovic], [Miguel Morales], and [Joshua R. Smith] from the University of Washington, which purports to construct a low-throughput RF transmitter from little more than a resistor.

This witchcraft is made possible thanks to Johnson noise, also known as Johnson-Nyquist noise, which is the white noise generated by charge carriers in a conductor. In effect, the movement of electrons in a material thanks to thermal energy produces noise across the spectrum. Reducing interference from Johnson noise is why telescopes often have their sensors cooled to cryogenic temperatures. Rather than trying to eliminate Johnson noise, these experiments use it to build an RF transmitter, and with easily available and relatively cheap equipment. Continue reading “A Single-Resistor Radio Transmitter, Thanks To The Power Of Noise”

Four images in one. Top left is an image of four individuals in a room with whiteboards and desks in the background along with various clutter on the floor. Over the people is a wireframe overlay of their poses. The image on the top right is just the wireframe people on a black background. Bottom left image is of a single individual standing in a room with the pose wireframe overlay. Bottom right image is the single pose wireframe on a black background.

Tracking Humans With WiFi

In case you thought that cameras, LiDAR, infrared sensors, and the like weren’t enough for Big Brother to track you, researchers from Carnegie Mellon University have found a way to track human movements via WiFi. [PDF via VPNoverview]

The process uses the signals from WiFi routers for an inexpensive way to determine human poses that isn’t hampered by lack of illumination or object occlusion. The system produces UV coordinates of human bodies by analyzing signal strength and phase data to generate a 2D feature map and then feeding that through a modified DensePose-RCNN architecture which corresponds to 3D human poses. The system does have trouble with unusual poses that are not in the training set or if there are more than three subjects in the detection area.

While there are probably applications in Kinect-esque VR Halo games, this will probably go straight into the toolbox of three letter agencies and advertising-fueled tech companies. The authors claim this to use “privacy-preserving algorithms for human sensing,” but only time will tell if they’re correct.

If you’re interested in other creepy surveillance tools, checkout the Heat-Sensing Crotch Monitor or this Dystopian Peep Show.

Wireless CNC Pendant Implemented With ESP-NOW

As a fervent fan of twiddly and twirly widgets and tactile buttons in a device’s user interface, [Steve M Potter] created a remote control (pendant) for his CNC machine, which he explains in a recent video that’s also linked down below. In addition to all the tactile goodness, what is perhaps most interesting about this controller is that it uses Espressif’s ESP-NOW protocol. This still uses the same 2.4 GHz as WiFi would, but uses a system more akin to the pairing of a wireless mouse or keyboard.

Advantages of ESP-NOW include the lower power usage, longer range, no requirement for a router and WiFi SSID & password. As far as latency goes, [Steve] measured a round-trip latency of 2.4 ms, which is fast enough for this purpose. Since it does control a potentially dangerous machine, all transmissions are acknowledged and re-transmitted at higher power if needed.

The lower power usage means that the pendant will last a lot longer on a single charge from the 18650 Li-ion cell, while ESP-NOW’s fixed address pairing saves time when turning the pendant on. Meanwhile, on the CNC side, another ESP32 acts as the receiving end for commands, although theoretically an ESP8266 could be used as well, if size or power was a concern there.

As for the transparent enclosure? It’s to make it easier to show it off to interested folk, apparently.

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A small brown PCB with various components on it. There is a headphone cable and DC barrel connector cable coming out of it.

Put Your Serial Port On The Web

Today, everything from your computer to your dryer has wireless communications built in, but devices weren’t always so unencumbered by wires. What to do when you have a legacy serial device, but no serial port on the computer you want to connect? [vahidyou] designed a wireless serial dongle to solve this conundrum.

Faced with a CNC that took instructions over serial port, and not wanting to deal with the cabling involved in a serial to USB adapter, [vahidyou] turned to an ESP8266 to let his computer and device talk wirelessly. The hand-made PCB connects via a 3.5 mm headphone jack to DB9 adapter which he describes in another article. While [vahidyou] did write a small Windows program for managing the device, it is probably easier to simply access it in a web browser from any device you have handy.

Want to see another wireless serial port application? This Palm Portable Keyboard Bluetooth dongle will let you type in comfort on the go, or you can use a PiModem to get your retrocomputer online!

Fritzing diagram of connections between the Wemos D1 board, the TP4056 board, the pushbutton and the LiIon battery

Battery-Powered ESP8266 Sensor? Never Been Simpler

Say, you’re starting your electronics journey with a few projects in mind. You have an ESP8266 board like the Wemos D1, a Li-Ion battery, you want to build a small battery-powered sensor that wakes up every few minutes to do something, and you don’t want to delve into hardware too much for now. Well then, does [Mads Chr. Olesen] have a tutorial for you! Here, you’ll learn the quick and easy way to get your sensor up and running, learn a few tricks for doing sleep Arduino environment, and even calculate how long your specific battery could last. Continue reading “Battery-Powered ESP8266 Sensor? Never Been Simpler”

Supercon 2022: Mooneer Salem Goes Ham With An ESP32

After being licensed as a ham radio operator since the early 2000s, you tend to start thinking about combining your love for the radio with other talents. In a 20-minute talk at Hackaday Supercon 2022, [Mooneer Salem] tells the story of one such passion project that combined software and radio to miniaturize a digital ham radio modulator.

[Mooneer] works as a software developer and contributes to a project called FreeDV (free digital voice), a digital voice mode for HF radio. FreeDV first compresses the digital audio stream, then converts it into a modulation scheme sent out over a radio. The appeal is that this can be understandable down to very low signal-to-noise ratios and includes metadata and all the other niceties that digital signals bring.

Traditionally, this has required a computer to compress the audio and modulate the signal in addition to two sound cards. One card processes the audio in and out of your headset, and another for the audio coming in and out of the radio. [David Rowe] and [Rick Barnich] developed the SM1000, a portable FreeDV adapter based around the STM32F4 microcontroller. However, flash space was running low, and the cost was more than they wanted. Continue reading “Supercon 2022: Mooneer Salem Goes Ham With An ESP32”