RF Modulation: Crash Course For Hackers

January 28, 2020 by Danie Conradie 16 Comments

When you’re looking to add some wireless functionality to a project, there are no shortage of options. You really don’t need to know much of the technical details to make use of the more well-documented modules, especially if you just need to get something working quickly. On the other hand, maybe you’ve gotten to the point where you want to know how these things actually work, or maybe you’re curious about that cheap RF module on AliExpress. Especially in the frequency bands below 1 GHz, you might find yourself interfacing with a module at really low level, where you might be tuning modulation parameters. The following overview should give you enough of an understanding about the basics of RF modulation to select the appropriate hardware for your next project.

Three of the most common digital modulation schemes you’ll see in specifications are Frequency Shift Keying (FSK), Amplitude Shift Keying (ASK), and LoRa (Long Range). To wrap my mechanically inclined brain around some concepts, I found that thinking of RF modulation in terms of pitches produced by a musical instrument made it more intuitive.

And lots of pretty graphs don’t hurt either. Signals from two different RF dev boards were captured and turned into waterfall and FFT plots using a $20 RTL-SDR dongle. Although not needed for wireless experimentation, the RTL-SDR is an extremely handy debugging tool, even to just check if a module is actually transmitting. Continue reading “RF Modulation: Crash Course For Hackers” →

Amazon’s AI Escapes Its Hardware Prison

August 4, 2015 by Brian Benchoff 47 Comments

It’s the 21st century, and we’re still a long way from the voice-controlled computers we were all promised in the 60s, 70s, 80s, and 90s. The state of voice interaction has improved, though, and Amazon’s release of the Alexa Skills Kit (ASK) is another sure step towards a future of computers that will pay attention to you. This allows any hardware to become Alexa, your personal voice assistant with the ability to do just about anything you command.

Up to this point, Alexa was locked away inside the Amazon Echo, the ‘smart’ cylinder that sits in your living room and does most of what you tell it to do. Since the Amazon Echo was released, we’ve seen the Echo and the Alexa SDK used for turning lights on and off, controlling a Nest thermostat, and other home automation tasks. It’s not Google Now, Microsoft’s Cortana, or Apple’s Siri that is behind all these builds; it’s Amazon’s Alexa that is bringing us into a world where Star Trek’s [Scotty] talking into an old Mac is seen as normal.

Right now, the Getting Started guide for the Alexa Skills Kit is focused more on web services than turning lights on and air conditioning off. Sample code for ASK is provided in JavaScript and Java, although we would expect 3rd party libraries for Python to start popping up any day now. If you want to run ASK on a Raspberry Pi or other small Linux computer, you’ll need a way to do voice capture; the Jasper project is currently the front-runner in this space.

We hope this changes the home automation game in a couple of different ways. First, the ASK processes everything in the cloud so very low power devices are now ready for some seriously cool voice interaction. Second, Amazon’s move to open up what you can do with the software backend means a community developing for the hardware could eventually exert pressure on Amazon to do things like making the system more open and transparent.

Already working on some hacks with the Echo or ASK? Send in a tip to your write-up and tells us about it in the comments below.

Control Nest Devices With Amazon Echo

July 25, 2015 by Rick Osgood 15 Comments

[ZPriddy] was looking for a way to control his Nest thermostats with Amazon Echo. He didn’t want to settle for using AWS or some other hosted service. [ZPriddy] wanted something that he could host and manage completely on his own. The end result is what he calls EchoNestPy.

[ZPriddy] started by learning how to use the Alexa Skills Kit (ASK). ASK is the official SDK that allows enthusiasts to add functionality to their Amazon Echo. Unfortunately for [ZPriddy], most of the example code he found was designed to be used on Amazon Lambda, but that didn’t stop him. After finding a few examples of Amazon Echo requests and responses, he was on his way.

[ZPriddy] chose to implement a simple web server using Flask. The web server listens for the Amazon requests and responds appropriately. It also Oauth2 authentication to ensure some level of security. The server is capable of synchronizing the temperature of multiple Nest devices in the same home, but it can also increment or increment the temperature across the board. This is accomplished with some simple voice commands such as “Tell Nest that I’m a little bit chilly”. If you like Amazon Echo hacks, be sure to check out this other one for controlling WeMo devices. Continue reading “Control Nest Devices With Amazon Echo” →

Over-engineering Ding Dong Ditch

December 11, 2014 by Brian Benchoff 20 Comments

One day, [Samy]’s best friend [Matt] mentioned he had a wireless doorbell. Astonishing. Even more amazing is the fact that anyone can buy a software defined radio for $20, a small radio module from eBay for $4, and a GSM breakout board for $40. Connect these pieces together, and you have a device that can ring [Matt]’s doorbell from anywhere on the planet. Yes, it’s the ultimate over-engineered ding dong ditch, and a great example of how far you can take practical jokes if you know which end of a soldering iron to pick up.

Simply knowing [Matt] has a wireless doorbell is not enough; [Samy] needed to know the frequency, the modulation scheme, and what the doorbell was sending. Some of this information can be found by looking up the FCC ID, but [Samy] found a better way. When [Matt] was out of his house, [Samy] simply rang the doorbell a bunch of times while looking at the waterfall plot with an RTL-SDR TV tuner. There are a few common frequencies tiny, cheap remote controls will commonly use – 315 MHz, 433 MHz, and 900 MHz. Eventually, [Samy] found the frequency the doorbell was transmitting at – 433.8 MHz.

After capturing the radio signal from the doorbell, [Samy] looked at the audio waveform in Audacity. It looked like this doorbell used On-Off Keying, or just turning the radio on for a binary ‘1’ and off for a binary ‘0’. In Audacity, everything the doorbell transmits becomes crystal clear, and with a $4 434 MHz transmitter from SparkFun, [Samy] can replicate the output of the doorbell.

For the rest of the build, [Samy] is using a mini GSM cellular breakout board from Adafruit. This module listens for any text message containing the word ‘doorbell’ and sends a signal to an Arduino. The Arduino then sends out the doorbell code with the transmitter. It’s evil, and extraordinarily over-engineered.

Right now, the ding dong ditch project is set up somewhere across the street from [Matt]’s house. The device reportedly works great, and hopefully hasn’t been abused too much. Video below.

Continue reading “Over-engineering Ding Dong Ditch” →

Sniffing PH Sensor RF Signals For Feedback Re: Your Esophagus

March 31, 2014 by Mathieu Stephan 8 Comments

For about a week [Justin] had a wireless acidity level sensor in his esophagus and a pager-looking RF receiver in his pocket. So he naturally decided to use an RTL-SDR dongle to sniff the signals coming out of him. As most of our Hackaday readers know, these cheap RTL2382U-based DVB-T receivers are very handy when it comes to listening to anything between 50MHz and 1800MHz. [Justin] actually did a great job at listing all the things these receivers can be used for (aircraft traffic monitoring, weather images download, electric meter reading, pacemaker monitoring…).

After some Googling he managed to find his Bravo pH sensor user’s guide and therefore discovered its main frequency and modulation scheme (433.92MHz / ASK). [Justin] then used gqrx and Audacity to manually decode the packets before writing a browser-based tool which uses an audio file. Finally, a few additional hours of thinking allowed him to extract his dear esophagus’ pH value.

Super Serious Garage Door Opener

October 24, 2012 by Eric Evenchick 17 Comments

Tired of cheap plastic garage door openers? [Yetifrisstlama]’s is probably the most serious garage door opener that we’ve seen. The case is an old emergency stop switch, which has plenty of space for the circuitry and features a big red button.

This build log starts with details on reverse engineering the original door opener’s protocol. It’s an amplitude-shift keying (ASK) signal that sends a 10 bit code to authenticate. The main components inside are a PIC16LF819 microcontroller, a MAX7057 ASK/FSK transmitter, and some RF circuitry needed to filter the signal. There’s a mix of through hole and surface mount components mounted on a prototyping board, requiring some crafty soldering.

[Yetifrisstlama] says that the next step is to add a power amplifier to increase the range. The code and project files are also provided for anyone interested in working with ASK. While the hack looks awesome, it might make bystanders think you’re doing something more sinister than opening a garage door.

Ask HackADay: Organization?!

April 15, 2010 by Jakob Griffith 34 Comments

Several people have been asking a similar question to,

“How do you at Hackaday keep track of and organize all your equipment?”
-[Jeff Allen] and others.

We have a variety of resources to help you keep track of your tools, equipment, parts, and supplies! Follow us after the jump for some tips for keeping your workspace clean and tidy. Continue reading “Ask HackADay: Organization?!” →