DVB-S From a Raspberry Pi with No Extra Hardware

An exciting aspect of the trend in single board computers towards ever faster processors has been the clever use of their digital I/O with DSP software to synthesize complex signals in the analogue and RF domains that would previously have required specialist hardware. When we use a Raspberry Pi to poll a sensor or flash an LED it’s easy to forget just how much raw processing power we have at our fingertips.

One of the more recent seemingly impossible feats of signal synthesis on a Raspberry Pi comes from [Evariste Courjaud, F5OEO]. He’s created a DVB-S digital TV transmitter that produces a usable output direct from a GPIO pin, with none of the external modulators that were a feature of previous efforts required. (It is worth pointing out though that for legal transmission a filter would be necessary.)

DVB is a collection of digital TV standards used in most of the world except China and the Americas. DVB-S is the satellite version of DVB, and differs from its terrestrial counterpart in the modulation scheme it employs. [Evariste] is using it because it has found favor as a digital mode in amateur radio.

This isn’t the first piece of [F5OEO] software creating useful radio modes from a GPIO pin. He’s also generated SSB, AM, and SSTV from his Pi, something which a lot of us in the amateur radio community have found very useful indeed.

We’ve covered digital TV creation quite a few times in the past on these pages, from the first achievement using a PC VGA card almost a decade ago to more recent Raspberry Pi transmitters using a USB dongle and a home-built modulator on the GPIO pins. Clever signal trickery from digital I/O doesn’t stop there though, we recently featured an astoundingly clever wired Ethernet hack on an ESP8266, and we’ve seen several VHF NTSC transmitters on platforms ranging from the ESP to even an ATtiny85.

Thanks [SopaXorzTaker] for the nudge to finally feature this one.

Digital TV converter reverse engineering

Back when broadcast television was first switching over from analog to digital most people needed to get a converter box to watch DTV broadcasts. Remember that abomination that was “HD-Ready”? Those TVs could display an HD signal, but didn’t actually have a digital tuner in them. Nowadays all TVs come with one, so [Craig] found his old converter box was just gathering dust. So he cracked it open and reverse engineered how the DTV hardware works.

The hardware includes a Thompson TV tuner, IR receiver for the remote control, and the supporting components for an LGDT1111 SoC. This is an LG chip and after a little searching [Craig] got his hands on a block diagram that gave him a starting place for his exploration. The maker of the converter box was also nice enough to include a pin header for the UART. It’s populated and even has the pins labeled on the silk screen. We wish all hardware producers could be so kind. He proceeds to pull all the information he can through the terminal. This includes a dump of the bootloader, readout of the IR codes, and much more.