Using an LED as a Simple RF Detector

When [b.kainka] set out to make the world’s simplest RF detector, he probably didn’t realize it would be as easy as it was. Consisting of only a handful of components and thirty eight lines of code, he was able to make an RF detector that works reasonably well.

The microcontroller running the code is an ATtiny13 on a Sparrow board. He’s using an everyday LED as a detector diode and an internal pull-up resistor in the ATtiny13 for the bias voltage. The antenna runs off the LED’s anode. To make it sensitive enough, he switches on the pull-up resistor for a tiny fraction of time. Because an LED can act like a small capacitor, this charges it to a few volts. He then switches the pullup off, and the voltage across the LED will start to discharge. If there is an RF signal present, the discharge voltage will be less than the discharge voltage with no signal present.  Neat stuff.

Be sure to check out his Hackaday.io page linked at the top for full source, schematics and some videos demonstrating his project.

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Using MATLAB and SDR to Reverse Engineer 433MHz Messages

Hackers everywhere are having a lot of fun with SDR – as is obvious from the amount of related posts here on Hackaday. And why not, the hardware is cheap and easily available. There are all kinds of software tools you can use to dig in and explore, such as SDR# , Audacity, HDSDR and so on. [illias] has been following SDR projects for a while, which piqued his interest enough for him to start playing with it. He didn’t have any real project in mind so he focused on studying the methodology and the tools available for analyzing 433MHz RF transmission. He describes the process of using MATLAB to recover the transmissions being received by the SDR

He started off by studying the existing tools available to uncover the details of the protocol. The test rig uses an Arduino UNO with the rc-switch library to transmit via a common and inexpensive 433MHz module. SDR# is used to record the transmissions and Audacity allows [illias] to visualize the resulting .wav files. But the really interesting part is where he documents the signal analysis using MATLAB.

He used the RTL-SDR package in conjunction with the Communications System Toolbox to perform spectrum analysis, noise filtering and envelope extraction. MATLAB may not be the easiest to work with, nor the cheapest, but its powerful features and the fact that it can easily read data coming from the SDR makes it an interesting tool. For the full skinny on what this SDR thing is all about, check out Why you should care about Software Defined Radio.

WiFi Controlled Power Outlets with Raspberry Pi

[Tim] was looking for a way to control his power outlets using WiFi. He looked into purchasing a WeMo but he realized that he could build something even better with more bang for his buck. He started out by purchasing a five pack of Etekcity wireless remote control outlet switches. These are kind of like the WeMo, only they aren’t controlled via WiFi. Instead, they come with an RF controller. [Tim] just needed to find a way to bridge the gap between the RF remote and WiFi.

[Tim] decided to use a Raspberry Pi as the brains of the controller. He also purchased a SMAKN 433MHz RF receiver and transmitter for communicating with the wireless outlet switches. The wiring for the modules is pretty simple. There are only four wires. There are power and ground wires for each module. Then the transmitter needs two GPIO pins while the receiver only needs one.

[Tim] began with a fresh installation of Raspbian. He then installed Wiring Pi, which gives you the ability to interface with the GPIO pins in a way that is similar to Arduino. He also installed Apache and PHP to create a web interface for switching the outlets. The last step was to write some custom software. The software included a script that allowed [Tim] to sniff out the controls of his RF remote. The correct codes are entered into the “toggle.php” file, and everything is set. All [Tim] has to do now is browse to his Pi’s web server and click a button. All of the custom code is available via git.

2014 Advent Calender of Circuits

Every day this month and until Christmas, [vk2zay] is (has already been!) posting a simple but useful hack in his 2nd sort-of-annual “Advent Calender of Circuits” that many of you will want to be bookmarking. For those already saturated with the season of holiday hacks, don’t worry – other than being festively generous of him to tutor and demo a new hack every day, the hacks themselves have nothing to do with Christmas. Though he missed the last couple years we here at Hackaday covered his first month of hacks back in 2011 (now in playlist).

The daily hacks posted so far cover a wide variety of useful projects (leaning towards HV) for the electronics hobbyist who might not have all the fancy tools in their shop: DIY high voltage probes, a 1-hour tesla coil from junk, measuring RF power, a stud detector, how to test an  unknown transformer’s saturation, and many others. We cannot predict what will be posted the rest of the calender (the author hints to be making them up as he goes), but by now it is safe to say that they will not disappoint.

We would be stealing his thunder to cover them all, so, we will just pick our favorite for now:

The 1-hour tesla coil is a delightful all-shortcuts-taken hack project. If one were to listen to aficionados, teslacoiling is a highly precise hobby to get into. It appears to require careful planning, much calculation, special-ordered or soviet-surplus parts, custom jigs, fine tuning, etc. [vk2zay] shows otherwise.

Every single component of the assembly is itself a hack.

No fancy tungsten-infused grade 8 copper being water-cooled via heat pump here – the spark gap is just the bent leg of a capacitor hovering near the start of the primary winding. The power supply is a backlight inverter with a chain of Cockcroft-Walton voltage doublers. The high voltage resistor is a bunch of series-chained resistors shoved into a silicone tube. The topload is a couple cheap pie tins masking-taped together to “resemble something like a sphere.” The primary is a loose, unsupported spring of copper wire. The secondary was calculated to be whatever the height of the tube he had handy and coiled only as smoothly as a first attempt would allow. He does not even bother using wires or a switch – the circuit is completed by clipping a couple of test leads.

After all this hodgepodgery the circuit was then carefully tuned to optimize how little time it took to build (additional time used: zero). Since the frequencies do not match (1.7 vs. 2.6 mhz – 35% apart) the only thing this circuit resonates with is a hacker’s appeal for making do. Does not matter, still works. The streamers easily reach 2 inches and the author claims double that in dark lighting.

In the just 6 minute video he also manages to explain roughly what is going on theory-wise and suggest the time-effective things to considering upgrading. Almost a dozen hacks in the bag and over a dozen more to come before Christmas.

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Christmas Lights And Ships In A Bottle

Thanksgiving was last week, and Christmas has been invading department stores for two or three months now, and that can only mean one thing: it’s time to kill a tree, set it up in your living room, and put a few hundred watts of lights on it. All those lights, though; it’s as if Christmas lights were specifically invented as fodder for standup comedians for two months out of the year. Why can’t someone invent wireless Christmas lights?

We don’t know if it’s been invented, but here’s a Kickstarter campaign that’s selling that same idea. It’s called Aura, and it’s exactly what it says on the tin: wireless Christmas lights, controllable with a smartphone. If it works, it’s a brilliant idea.

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Five Dollar RF Controlled Light Sockets

This is tens of thousands of dollars worth of market research I’m about to spill, so buckle up. I have a spreadsheet filled with hundreds of projects and products that are solutions to ‘home automation’ according to their creators. The only common theme? Relays. Home automation is just Internet connected relays tied to mains. You’re welcome.

[Todd] over at Fabricate.io found an interesting home automation appliance on Amazon; a four-pack of remote control light sockets for $20, or what we would call a microcontroller, an RF receiver, and a relay. These lamp sockets are remote-controlled, but each package is limited to four channels. Terrible if you’re trying to outfit a home, but a wonderful exploration into the world of reverse engineering.

After cracking one of these sockets open, [Todd] found the usual suspects and a tiny little 8-pin DIP EEPROM. This chip stores a few thousand bits, several of which are tied to the remote control. After dumping the contents of the EEPROM from the entire four-pack of light sockets, [Todd] noticed only one specific value changed. Obviously, this was the channel tied to the remote. No CRC or ‘nothin. It doesn’t get easier than this.

With the new-found knowledge of what each lamp socket was looking for, [Todd] set out to clone the transmitter. Tearing this device apart, he found a chip with HS1527 stamped on it. A quick Googling revealed this to be an encoder transmitter, with the datasheet showing an output format of a 20-bit code and four data bits. This was a four-channel transmitter, right? That’s where you put each channel. The 20-bit code was interesting but not surprising; you don’t want one remote being able to turn of every other 4-pack of lamp sockets.

With all the relevant documentation, [Todd] set out to do the obvious thing – an Arduino transmitter. This was simply an Arduino and a transmitter in the right frequency, loaded up with bit of carefully crafted code. [Todd] also figured out how to expand his setup to more than four lamp sockets – by changing the 20-bit code, he could make his Arduino pretend to be more than one transmitter.

With Arduino-controlled lamp sockets, the world is [Todd]’s oyster. He can add Ethernet, WiFi, Bluetooth LE, and whatever trendy web front end he wants to have a perfect home automation setup. It’s actually a pretty impressive build with some great documentation, and is probably the cheapest way to add Arduino/Internet-enabled relays we’ve ever seen.

 

Retrotechtacular: How to Teletypewriter

This week, you’re going to learn the ins and outs of the AN/GRC-46 thanks to this army training film from 1963. What is the AN/GRC-46, you ask? Why it’s a complete mobile-tactical sheltered radio-teletypewriter rig capable of CW, voice, and teletype transmission.

The film covers the components that make up the AN/GRC-46, their functions, the capabilities of the system, and proper operation procedures. There’s a lot going on in the tiny 1400lb. steel shelter, so each piece will be introduced from the ground up.

You’ll become familiar with the voltage distribution system and the AN/GRC-46’s included accessories. This introduction will be followed by a short course in RF signal transmission and the Frequency-Shift Keying (FSK) that is performed by the modulator. The ranges of both the transmitter and receiver are discussed, along with the capabilities mentioned before: CW operation using the keyer, voice operation, teletype operation, and reperforation of teletype tape.

Finally, you’ll observe a seasoned operator make contact and send a teletype message with movements so careful and deliberate that they border on mesmerizing. When he’s not sending messages or taking long walks on the beach, he can usually be found cleaning and/or lubricating the transmitter filter.

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