1998' Robotron plotter - renovation

Equipping the old-made (but not used) plotter with Bluetooth COM-port. Then making the first PCB and case's backplate with it.

What for? Why not ordinary printers? It is possible to draw PCB on this plotter, face panel of a case, to mount a laser/mechanical cutter and a mechanical engraver. Drawing area of this plotter is 370х270 mm (3700x2700 steps with 0.1 mm resolution).

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This plotter was made in DDR, but didn't work even once since 1989, and was kept in its original package. In 2019 he was powered for the first time and works without any problems.

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Some bulged capacitors were on PCBs. All electrolytic capacitors were replaced with new one.

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No other elements of the plotter looks requiring a repair.

This plotter is very heavy (16 kg), requires a lot of space, smells like warm oil, especially while working. No chance to place it on a table near a home computer, the best idea is to place it in the "far corner". But in this case, some wireless interface is needed. Here for this plotter was added Bluetooth interface.

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This plotter had V.24 interface (i.e. RS232) with 9600,N,8,1 parameters. In this project, the Bluetooth interface was added to the plotter via V.24 slot.

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Bolutek BK3231 module was used as the Bluetooth 2.1 receiver with COM interface for Windows OS. With AT-commands, parameters 9600,N,8,1 were tuned within this module.

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The RS232 to UART adapter was used for interfacing Bolutek BK3231 and plotter's V.24. Only two wires (Rx and Tx) were used from the plotter's V.24 slot - crosswise to Tx and Rx (pins 3 and 2 of RS232 slot) of the RS232 to UART adapter.

From the other side, Rx and Tx of Bolutek BK3231 module were soldered (no crosswise) to UART Rx and Tx of the RS232 to UART adapter.

Any DC/DC adapter needs to step down the plotter's 5V or 12V to the 3.3V needed for Bolutek BK3231. Same 3.3V was used for the RS232 to UART adapter.

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After soldering wires between modules and the plotter, all newly added modules were placed in a cosy place inside the plotter. The antenna of the Bolutek BK3231 module was faced to the plastic side of the plotter case (other case's parts of this plotter is metall).

Once the plotter was powered on, the Bluetooth device was found in Windows Bluetooth manager. Then the connection was established with PIN. New created COM-port was found in Windows Device Manager (here was COM14).

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Any utility for COM-port can be now used for the sending commands to the plotter. Here was used SUDT AccessPort. Serial port settings were 9600,N,8,1.

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No flow control was selected.

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For example, command OI; returns the name of the plotter.

Only the subset of HP-GL this plotter can execute. For example, PUx,y[{xn,yn}], PDx,y[{xn,yn}] not supported and must be replaced with PU;PAx,y[{xn,yn}] and PD;PAx,y[{xn,yn}] respectively. Another bad side is the very small buffer of the plotter - 512 bytes.

Any unacquainted command of this plotter is rejected without any reaction. Bytes can be sent to the plotter one by one, not with full command's string, that makes the buffer control easy.

As result was written this very simple Node.js script, it only send bytes one by one to the COM port once per 0.1 second, and wait for the "free buffer" flag from the plotter, if the "full buffer" flag or the "error flag" has received from the plotter. The file name for send to the plotter and the number of the COM port, need to be noted in the first lines of this script. Modules fs and serialport need to be installed for Node.js.

The HP-GL file can be produced with a dozen programs, such as CAD/CAM, vectorizers, vector graphics editors, etc. First of all - within Inkscape. As a rule, these days only linear movement is used within an HP-GL file. Before sending the HP-GL to the plotter with script above, only need to replace in this file all "PU" to the "PU;PA" and all "PD" to the "PD;PA" within any text editor (this is easily done with the "Find All and Replace" command).

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The only need to note about producing HP-GL file from the Inkscape is Resolution = 254.0 dpi and Curve flatness = 1.0.

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The first things made with this renovated plotter was a PCB for audio amplifier's AC/DC adapter...

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... and the backplate for the case of this amplifier.

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Probably the first...

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.. and the second experiments turned out well.

Afterword. As this article was published, folks are reminding that UV EPROMs (five M2716 type chips installed in this plotter) have the limited guarantee time for storage of data (25 years for best consumer versions of UV EPROMs). In the next article, the prophylactic replacement of EPROMs had described.

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