Your USB Serial Adapter Just Became A SDR

December 6, 2018 by Tom Nardi 39 Comments

To say that the RTL-SDR project was revolutionary might be something of an understatement. Taking a cheap little USB gadget and using it as a Software Defined Radio (SDR) to explore the radio spectrum from the tens of megahertz all the way into gigahertz frequencies with the addition of nothing more than some open source tools may go down as one of the greatest hacks of the decade. But even in the era of RTL-SDR, what [Ted Yapo] has manged to pull off is still pretty incredible.

With a Python script, a length of wire attached to the TX pin, and a mastery of the electron that we mere mortals can only hope to achieve, [Ted] has demonstrated using a common USB to serial adapter as an SDR transmitter. That’s right, using the cheap little UART adapter you’ve almost certainly got sitting in your parts bin right now and his software, you can transmit in the low megahertz frequencies and even up into VHF with some trickery. The project is still very much experimental, and though this may be the first time, we’re willing to bet this isn’t the last time you’ll be hearing about it.

The basic idea is that when sending certain characters over the UART serial line, they can combine with the start and stop bits to produce a square wave burst at half the baud rate. [Ted] found that sending a string of 0x55 at 19200 baud would generate a continuous square wave at 9600 Hz, and if he turned the baud rate all the way up to 2,000,000 where these USB adapters top out, that signal was transmitted at 1 MHz, right in the middle of the AM dial.

A neat trick to be sure, but alone not terribly useful. The next step was to modulate that signal by sending different characters over UART. [Ted] explains at great length his experiments with multi-level quantization and delta-sigma schemes, and each step of the way shows the improvement of the transmitted audio signal. Ultimately he comes up with a modulation scheme that produces a impressively clean signal, all things considered.

This alone is impressive, but [Ted] isn’t done yet. He realized that this method of transmission was generating some strong frequency harmonics which extended far beyond the theoretical maximum 1 MHz frequency of his UART SDR. In his experimentation he found he was able to pick up a signal from all the way out to 151 MHz, though it was too poor to be of any practical use. Dialing back the expectations a bit, he was able to successfully control a cheap 27 MHz RC toy using the 43rd harmonic of a 631 kHz signal at a range of about 10 feet with a FT232RL adapter, which he notes produces the cleanest signals in his testing.

[Ted] is still working on making transmissions cleaner and stronger by adding filters and amplifiers, but these early accomplishments are already very promising. His work reminds us of a low frequency version of the USB to VGA adapter turned GHz SDR transmitter, and we’re very eager to see where it goes from here.

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Adafruit Interviews The CEO Of FTDI

February 8, 2016 by Brian Benchoff 117 Comments

When it comes to electronic hobbyists and EEs, there is no company that deserves a few raised eyebrows than FTDI. They made their name with USB converter chips, namely USB to serial chips that are still very popular today. So popular, in fact, that clones of these chips are frequently found in the $2 Arduinos from China, and other very low-cost devices. A little more than a year ago, a few clever people noticed FTDI drivers were bricking these counterfeit chips by setting the USB PID to 0000. The Internet reacted to this move and FTDI quickly backed down from that position. The Windows driver was fixed, for about a year until the same shenanigans were found again.

Adafruit recently sat down with [Fred Dart], CEO of FTDI, giving us all the first facts and figures that aren’t from people frustrated with Windows’ automatically updated drivers. The most interesting information from [Fred Dart] is how FTDI first found these counterfeit chips, what FTDI chips are being counterfeited, and how many different companies are copying these chips.

The company first realized they were being cloned when they couldn’t reproduce results of a Chinese-made ‘FTDI’ USB to RS232 cable that behaved strangely. A sample of the cables were shipped to FTDI and after inspecting the chip inside, FTDI found it was a clone with a significantly different architecture than a genuine chip.

So far, the counterfeiters appear to only be counterfeiting the SSOP version of the FT232RL and occasionally the older FT232BL chip. From what FTDI has seen, there appears to be only one or two companies counterfeiting chips.

As the CEO of FTDI, [Fred] has a few insights into what can be done to stop counterfeiters in China. The most important is to trademark the logo. This isn’t just the logo for a webpage, but one that can be laser etched onto the plastic package of the chip. US Customs has been very amenable to identifying counterfeit components, and this has led to several shipments being destroyed. Legal action, however, is a bit hard in China, and FTDI is dealing with a gang that counterfeits more than FTDI chips; there’s a high likelihood this gang was responsible for the fake Prolific PL23o3 chips a few years ago.

As far as FTDI bricking counterfeit chips is concerned, [Fred Dart] wasn’t silent on the issue, he merely wasn’t asked the question and didn’t bring it up himself.

DIY ESP8266 Development Board

June 12, 2015 by Anool Mahidharia 10 Comments

Those small, super-cheap, ESP8266 modules are being installed everywhere, creating all sorts of frivolous internet connected thingamajigs. But consider this period as a training ground of sorts, as hackers smarten their chops on figuring out how to get the best out of this IoT gravy train. Right now, getting the ESP8266 to work requires a fair amount of work and to make things easier, [Abdulgafur] built a ESP8266 development board.

The dev board lets the user connect the ESP8266 to a PIC micro controller as well as to a host PC. In addition, it hosts several peripherals such as a 2×16 LCD display, 4 push buttons, couple of indicator LEDs and some GPIO’s broken out to a header. PC communication is via a FT232RL USB-UART converter over a Mini-USB connector. There’s also a few bi-directional level converters to translate between 5V and 3.3V and pull-up resistors for the ESP8266.

As of now, the dev board only supports the ESP8266-01 module. A nice upgrade would be to add support for other ESP8266 modules too. Maybe a separate, 3d printed, pogo pinned, test fixture for the other modules. If you plan to build you own version, [Abdulgafur] has the schematic, PCB and BoM available for download, although we couldn’t spot the PIC code, so you might have to ask for that. And it would be a good idea to remove the GND copper pour from under the ESP8266 footprint.