When wired networking or data connections can’t be made, for reasons of distance or practicality, various wireless protocols are available to us. Wi-Fi is among the most common, at least as far as networking personal computers is concerned, but other methods such as LoRa or Zigbee are available when data rates are low and distances great. All of these methods share one thing in common, though: their use of radio waves to send data. Using other parts of the electromagnetic spectrum is not out of the question, though, and [mircemk] demonstrates using light as the medium instead of radio.
Although this isn’t a new technology (“Li-Fi” was first introduced in 2011) it’s not one that we see often. It does have a few benefits though, including high rates of data transmission. In this system, [mircemk] is using an LED to send the information and a solar cell as the receiver. The LED is connected to a simple analog modulator circuit, which takes an audio signal as its input and sends the data to the light. The solar cell sends its data, with the help of a capacitor, straight to the aux input on a radio which is used to convert the signal back to audio.
Some of the other perks of a system like this are seen here as well. The audio is clear even as the light source and solar cell are separated at a fairly significant distance, perhaps ten meters or so. This might not seem like a lot compared to Wi-Fi, but another perk shown is that this method can be used within existing lighting systems since the modulation is not detectable by the human eye. Outside of a home or office setting, systems like these can also be used to send data much greater distances as well, as long as the LED is replaced with a laser.
Continue reading “Wireless Data Connections Through Light”
This week, we’re taking the wayback machine to 1940 for an informative, fast-paced look at the teleprinter. At the telegram office’s counter, [Mary] recites her well-wishes to the clerk. He fills out a form, stuffs it into a small canister, and sends it whooshing through a tube down to the instrument room. Here, an operator types up the telegram on a fascinating electro-mechanical device known as a teleprinter, and [Mary]’s congratulatory offering is transmitted over wires to her friend’s local telegraph office hundreds of miles away.
We see that the teleprinter is a transceiver that mechanically converts the operator’s key presses into a 5-digit binary code. For example, ‘y’ = 10101. This code is then transmitted as electrical pulses to teleprinters at distant offices, where they are translated back into alphanumerical data. This film does a fantastic job of explaining the methods by which all of this occurs and does so with an abstracted, color-coded model of the teleprinter’s innards.
The conversion from operator input to binary output is explained first, followed by the mechanical translation back to text on the receiving end. Here, it is typed out on a skinny paper tape by the type wheel shown above. Telegraphists in the receiving offices of this era cut and pasted the tape on a blank telegram in the form of meaningful prose. Finally, it is delivered to its intended recipient by a cheeky lad on a motorbike.
Continue reading “Retrotechtacular: Teleprinter Tour, Teardown”
Thought GNU Radio was just for radio? Think again. [Chris] has been hard at work turning the signal generation and analysis of the best tool for software defined radio into a networking device for speakers and a microphone.
The setup uses GNU Radio to generate a carrier signal whose frequency is modulated with a data stream. With this modulated signal piped over a laptop’s speakers, [Chris] is able to send UDP packets across his desk using nothing but sound.
[Chris] had recently used a similar technique to transmit data via audio with GNU Radio, but this latest build is a vast improvement; this is now a duplex networking, meaning two computers can transmit and receive at the same time.
In the end, [Chris] created a strange, obsolete device called a “modem”. It’s not exactly fast; sending ‘Hello World’ takes quite a bit of time, as you can see in the video below.
Continue reading “Audio Networking With GNU Radio”
When we hear GNU Radio was used in a build, the first thing we think of is, obviously, radio. Whether it’s a using extremely expensive gear or just a USB TV tuner dongle, GNU Radio is the perfect tool for just about everything in the tail end of the electromagnetic spectrum.
There’s no reason GNU Radio can’t be used with other mediums, though, as [Chris] shows us with his ultrasound data transmission between two laptops. He’s transmitting audio from the speakers of one laptop at 23 kHz. It’s outside the range of human hearing, but surprisingly able to be picked up by a cheap desktop mic connected to another laptop. His GNU Radio setup first converts a string of text to a 5-bit packet, modulates it with FSK, and bumps up the signal to 23 kHz. On the other end, the data is decoded by doing the same thing in reverse.
The setup is easily able to reject all audio that isn’t in the specified frequency range; in the video after the break, [Chris] successfully transmits a ‘hello world’ while narrating what he’s doing.
Continue reading “Ultrasonic Data Transmission With GNU Radio”