videotext

3 Articles

Ancient Cable Modem Reveals Its RF Secrets

April 22, 2024 by 27 Comments

Most reverse engineering projects we see around here have some sort of practical endpoint in mind. Usually, but not always. Reverse-engineering a 40-year-old cable modem probably serves no practical end, except for the simple pleasure of understanding how 1980s tech worked.

You’ll be forgiven if the NABU Network, the source of the modem [Jared Boone] tears into, sounds unfamiliar; it only existed from 1982 to 1985 and primarily operated in Ottawa, Canada. It’s pretty interesting though, especially the Z80-based computer that was part of the package. The modem itself is a boxy affair bearing all the hallmarks of 1980s tech. [Jared]’s inspection revealed a power supply with a big transformer, a main logic board, and a mysterious shielded section with all the RF circuits, which is the focus of the video below.

Using a signal generator, a spectrum analyzer, and an oscilloscope, not to mention the PCB silkscreen and component markings, [Jared] built a block diagram of the circuit and determined the important frequencies for things like the local oscillator. He worked through the RF section, discovering what each compartment does, with the most interesting one probably being the quadrature demodulator. But things took a decidedly digital twist in the last compartment, where the modulated RF is turned into digital data with a couple of 7400-series chips, some comparators, and a crystal oscillator.

This tour of 80s tech and the methods [Jared] used to figure out what’s going on in this box were pretty impressive. There’s more to come on this project, including recreating the original signal with SDRs. In the mean time, if this put you in the mood for other videotext systems of the 80s, you might enjoy this Minitel terminal teardown.

Continue reading “Ancient Cable Modem Reveals Its RF Secrets” →

Teletext In Ireland, Another Broadcasting Leftover Bites The Dust

October 13, 2023 by 14 Comments

Over the years we’ve reported on the passing of a few of the broadcasting technologies of yesteryear, such as analogue TV in America, or AM radio in Europe. Now it’s the turn of an early digital contender, as one of the few remaining holdouts of old-style teletext is to shut down its service. The Irish broadcaster RTÉ is to turn off its teletext service Aertel, which has been live in some form continuously since 1986.

Like all European countries, Ireland has had only digital TV for quite a few years now. The linked RTÉ piece implies that the Aertel service has been carried as the old-style data in the frame blanking period even when part of a digital multiplex rather than the newer digital teletext system, so we’d be really grateful if some of our Irish readers could flick on their TVs and confirm that.

In an internet-connected world it seems quaint that a limited set of curated pages could once have been such a big deal, but it’s easy to forget that for many the teletext system provided their first ever taste of online information. As it shuffles away almost unnoticed we won’t miss counting through the page numbers cycling by in the top corner as we waited for our page to load, but it’s worth marking its final passing from one of the few places it could still be found.

Teletext does pop up in a few projects here, most recently as the display engine for a game of DOOM.

Bring A Minitel Terminal Back To Life WIth An ESP32

November 25, 2021 by 11 Comments

Most of us who are old enough are likely to have had our first experience of an online service some time in the 1990s, either through the likes of Compuserve or via an ISP. For our French readers the online experience will have come much earlier, as a forward-thinking telecommunications environment led to every household in the country receiving a viewdata terminal. The Minitel system as it was called was a runaway success, and was only finally turned off as late as 2012. Many of the terminals survive to make a great basis for projects, and it’s one of these that [Louis H] has taken and enhanced with an ESP32.

One of the special things about this project is that unlike so many other Minitel conversions it doesn’t involve tearing into the terminal itself. Instead the PCB plugs into the socket on the back of the unit and emulates the line for the terminal to talk to. It can then be used as an SSH terminal over WiFi, or as a serial terminal for the ESP32 itself for example running a MicroPython firmware. If you can handle the French AZERTY keyboard there is no easier way to drag a viewdata terminal into the 2020s, as you can see in the video below the break.

Chez Hackaday, we love these nostalgic gems from the 1980s. Indeed we like this classic French public network so much that we’ve featured it quite a few times. Here for example is a similar project using an Arduino. Continue reading “Bring A Minitel Terminal Back To Life WIth An ESP32” →