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It’s probably fair to say that anyone reading these words understands conceptually how physically connected devices communicate with each other. In the most basic configuration, one wire establishes a common ground as a shared reference point and then the “signal” is sent over a second wire. But what actually is a signal, how do the devices stay synchronized, and what happens when a dodgy link causes some data to go missing?

All of these questions, and more, are addressed by [Ben Eater] in his fascinating series on data transmission. He takes a very low-level approach to explaining the basics of communication, starting with the concept of non-return-to-zero encoding and working his way to a shared clock signal to make sure all of the devices in the network are in step. Most of us are familiar with the data and clock wires used in serial communications protocols like I2C, but rarely do you get to see such a clear and detailed explanation of how it all works.

He demonstrates the challenge of getting two independent devices to communicate, trying in vain to adjust the delays on the receiving and transmitting Arduinos to try to establish a reliable link at a leisurely five bits per second. But even at this digital snail’s pace, errors pop up within a few seconds. [Ben] goes on to show that the oscillators used in consumer electronics simply aren’t consistent enough between devices to stay synchronized for more than a few hundred bits. Until atomic clocks come standard on the Arduino, it’s just not an option.

[Ben] then explains the concept of a dedicated clock signal, and how it can be used to make sure the devices are in sync even if their local clocks drift around. As he shows, as long as the data signal and the clock signal are hitting at the same time, the actual timing doesn’t matter much. Even within the confines of this basic demo, some drift in the clock signal is observed, but it has no detrimental effect on communication.

In the next part of the series, [Ben] will tackle error correction techniques. Until then, you might want to check out the fantastic piece [Elliot Williams] put together on I2C.

[Thanks to George Graves for the tip.]

We use the Internet to do everything from filing our taxes to finding good pizza, but most critically it fulfills nearly all of our communication needs. Unfortunately, this reliance can be exploited by those pulling the strings; if your government is trying to do something shady, the first step is likely to be effecting how you can communicate with the outside world. The Internet is heavily censored and monitored in China, and in North Korea the entire country is effectively running on an intranet that’s cutoff from the wider Internet. The need for decentralized information services and communication is very real.

While it might not solve all the world’s communication problems, [::vtol::] writes in to tell us about a very interesting communication device he’s been working on that he calls “Hot Ninja”. Operating on the principle that users might be searching for accessible Wi-Fi networks in a situation where the Internet has been taken down, Hot Ninja allows the user to send simple messages through Wi-Fi SSIDs.

We’ve all seen creatively named Wi-Fi networks before, and the idea here is very much the same. Hot Ninja creates a Wi-Fi network with the user’s message as the SSID in hopes that somebody on a mobile device will see it. The SSID alone could be enough depending on the situation, but Hot Ninja is also able to serve up a basic web page to devices which actually connect. In the video after the break, [::vtol::] even demonstrates some rudimentary BBS-style functionality by presenting the client devices with a text field, the contents of which are saved to a log file.

In terms of hardware, Hot Ninja is made up of an Arduino Mega coupled to three ESP8266 boards, and a battery to keep it all running for up to eight hours so you can subvert a dictatorship while on the move. The user interface is provided by a small OLED screen and a keyboard made entirely of through-hole tactile switches, further reinforcing the trope that touch-typing will be a must have skill in the dystopian future. It might not be the most ergonomic device we’ve ever seen, but the fact it looks like something out of a Neal Stephenson novel more than makes up for it in our book.

This is not the first time we’ve seen Wi-Fi SSIDs used as a method of communication, thanks largely to how easy the ESP8266 makes it. For his part, [::vtol::] has previously experimented with using them to culturally enrich the masses.

DIY Satellite builders have been at it since 1961Setting the record straight on the history of Do-It-Yourself satellites.

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