Vintage Plotter Gets Bluetooth Upgrade

Recently [iot4c] stumbled upon this gorgeous Robotron Reiss plotter from 1989, brand-new and still in its original box. Built before the fall of the Berlin Wall in East Germany, it would be a crime to allow such a piece of computing history to go unused. But how to hook it up to a modern system? Bad enough that it uses some rather unusual connectors, but it’s about to be 2020, who wants to use wires anymore? What this piece of Cold War hardware needed was an infusion of Bluetooth.

While the physical ports on the back of the Robotron certainly look rather suspect, it turns out that electrically they’re just RS-232. In practice, this means converting it over was fairly straightforward. With a Bolutek BK3231 Bluetooth module and an RS-232 to UART converter, [iot4c] was able to create a wireless adapter that works transparently on the plotter by simply connecting it to the RX and TX pins.

A small DC buck converter was necessary to provide 3.3 V for the Bluetooth adapter, but even still, there was plenty of room inside the plotter’s case to fit everything in neatly. From the outside, you’d have no idea that the hardware had ever been modified at all.

But, like always, there was a catch. While Windows had no trouble connecting to the Bluetooth device and assigning it a COM port, the 512 byte buffer on the plotter would get overwhelmed when it started receiving commands. So [iot4c] wrote a little script in Node.js that breaks the commands down into more manageable chunks and sends them off to the plotter every 0.1 seconds. With this script in place the Robotron moved under its own power for the first time in ~30 years by parsing a HP-GL file generated by Inkscape.

If you’re interested in a plotter of your own but don’t have a vintage one sitting around, never fear. We’ve seen an influx of DIY plotters recently, ranging from builds that use popsicle sticks and clothespins to customizable 3D printed workhorses.

20 thoughts on “Vintage Plotter Gets Bluetooth Upgrade

        1. Wow! You are right! Thank you very much for reminding me of this! The ROM chips are soldered, not on sockets, but I will try to find information on how to do this without unsoldering. I think this information should be … the controller of this plotter is made on the basis of Z80, so first of all I will look for a technique among users of ZX Spectrum.

  1. Could the issues with the tiny half-kilobyte buffer be dealt with simply by setting a really low old-fashioned baud rate? Like 300 baud or something. Maybe get a Bluetooth controller that has some of its own memory and set the baud rate low on the rs-232 adapter?

        1. The linked-to article’s website fails to load for me, so I can’t check the script. In the old HP plotters, at least, XON-XOFF mode needed to be explicitly enabled by an escape command, and the “high water mark” (where the printer would send the XOFF character) can be set. XON-XOFF flow control would not work until it was enabled.

    1. In this case the plotter running with jerkely and with unnecessary downtime. Therefore, additionally to the periodic commands send, was used work with overflow flags (11h and 13h) of the plotter’s buffer.

  2. Plotter drivers? Who needs that? Just open a command prompt and COPY /B the HPGL files to the serial port. With the flow control lines properly connected, the plotter controls when the data is sent. Don’t even need the /B (Binary) switch if the plot file is plain HPGL. For HPGL/2 sending in Binary mode is a good idea because HPGL/2 uses characters outside the basic ASCII set.

    If you have a need to plot the same file more than once, put the command in a one line batch file.

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