Hackaday Retro Edition: Hackadaying At 300 Baud


For a bottom of the barrel website like our retro edition, there’s little reason to have a fast Internet connection. Even the fastest hands in the land can barely type faster than 300 baud. The problem with low-speed connections is the overhead involved, as [Pierre] discovered when he dug out an acoustic modem from the ’80s and loaded up our retro site.

While this isn’t the first modem ever made – that’s 1960s tech – but it does operate at the same speed – 300 bits per second, or slower than you reading this sentence. [Pierre] stuck a desk phone into the modem’s cups, plugged it in to a phone line simulator, and connected to a Raspberry Pi equipped with another modem. From there, it was pretty easy to set up a terminal at 300 baud.

A serial connection isn’t a connection to the Internet, however, and at 300 baud, PPP is nearly impossible. The overhead of encapsulating packets is just that high. SLIP is a much better choice to send IP packets over a slow serial connection, but [Pierre]‘s mac doesn’t include the proper tools.

[Pierre] ended up using the serial connection between his Mac and Raspi with Zterm. From there, Lynx and Bob’s your uncle.

There’s an unsurprisingly long video of [Pierre] loading up the retro site below, as well an unsurprisingly long video of speedtest.net running at 56k.


  1. Biomed says:

    Made a lot of money building these for ppl back in ’80-83. Finding acoustic couplers was the big hurdle, made my own boards and rest of parts were easy to find. Also remember being threatened with a broom for a $300 phone bill I ran up with my own. Nostalgia.

    • Greenaum says:

      You made 300 baud modems? Interesting! How’d you do it? How do you decide what frequencies to use at each end, etc? I’d be interested to know as much as you want to tell, in fact it might make a good article for the Retrotechtacular. If they’re allowed to be anything other than Youtube videos.

      • Biomed says:

        If you’re from HAD you got my email.

        The board measured under 3″ x 3″, the schematic came straight out of a magazine, DATAK made it quick and simple for one board at a time. FSK standards all well published. It was no feat, just a service to buddies, cost only, no profit, just furthering the hobby for anyone dying to have one Needed an acoustic coupler first and found a supply. There was no magic peculiar to myself other than willingness to loan my skills to helping them out. I was president and founder of the local user group and had my own interests there.

        Have confirmed through phone call that the ex would still like to have me lynched for that $300 phone bill.

        It was the best of times… it was the worst of times….

        I helped. .

  2. rj says:

    CSLIP is more of less required for slow link speeds.

    I thought I’d remembered reading that there was a version of PPP with compressed headers that actually approached CSLIP levels of lack of overhead, but maybe I’m wrong, given this story.

    • Trui says:

      Correct. With CSLIP, the overhead per higher level protocol packet is 5 bytes. With PPP+VJ compression and minimal headers, the overhead is 6 bytes. So, the difference is minimal.

  3. Mystick says:

    300 Baud != 300 bps in all circumstances.

  4. Niek says:

    2:05 in second video -> RIP headphone users (like me sadly)

  5. Hi,

    I’m Pierre, and just a thing : the second video was an April Fool. The first, with the acoustic modem is real, the second is a fake for the 1st april.

  6. Luke says:

    300 baud? That’s fast! ASCII – so modern!

    In the eighties, I supervised a team that worked with diverse hardware/software and one member was maintaining a Baudot connection at 50 baud. Data originated in Washington DC and was sent to Toronto. He was the only person who knew how to program the big box containing a primitive computer (forget the name/brand) that processed the data. I doubt anyone uses it anymore, but it could be replaced by a single-board microcontroller today.

  7. Tim says:

    This is quite fascinating to me. Reminds me of wargames with the war dialing.

  8. NewCommentor1283 says:





    back then we actually made hardware-modems that were connected to a computer.
    Like with hardware frequency-detecting chips or even just reeeally tight filters

    nowadays we make 1200 baud modems with 2$ uC’s.

    PS: @Greenaum
    frequencys can be anything compatible with the phone system, as long as you are ONLY dialing a MATCHING custom-made modem. you will have problems you will need to solve, most solutions revolve around picking frequencys that work good with each other(duplex?). i highly suggest picking an existing standard, or at it’s frequencies. thats what i did.

    the following is a quote noone in buisness wants to admit to remembering

    “if you want to dial a host, first you need to enter in the specs (modulation, byteformat, bitrate, ect) for the particular host you are dialing… you DO know the specs of the host you are dialing dont you?”

    oh and the modem you have might not even be able to connect to the host because it’s not compatible.

    and for anyone thinking “how dare something such as this exists” …
    remember that there WAS NO ALTERNATIVE at the time and apple did not exist yet, so it was still usefull.

    • Biomed says:

      Hayes came along.. and was cheap. The need to roll your own went away, but you could still do it up to 2400 baud no problem. AT commands pushed it over the line and just made it too simple for the masses, and the masses went with that. We still use AT commands today. Past 1200 bps there was no point for the hobbiest…. easier, cheaper, and vastly more expedient to just by one. After all it was “just an accessory”, or for today’s language “Just a peripheral”. The computer was the target of interest for the hobby.

      You’re all right. But nobody has it all… and nobody has it right… it was a wonderful age.

    • Jonathan Wilson says:

      Then even later than the Hays stuff, some bright spark realized you could build an internal modem where most of the processing was done by the host CPU and the modem was just a DAC and level converter. And until broadband came along and made them obsolete, the winmodem (as became was known because the special drivers and implementation were Windows-only) was the bane of many a Linux geek.

  9. Biomed says:

    CP/M and Xmodem…. that made me a lotta cash. Code all prepared, just had to plunk in the UART type and address. People though me genius… I just smiled and stayed silent while writing out the bill… Printer cables were another good one. Flat fee $50. 30 minutes effort. Serial cables $30. Everybody wanted their new gadgets to work. Didn’t stand a chance of keeping up with the demand.

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