HP 7475A Plotter [Part 2]

It has been quite some while since I made my first post on the 7475a, it has been sitting in my closet neglected for months because of my move and I am back in classes now. But in need of several pcb’s for current projects I made a point to dust it off last weekend and see if we could etch some copper.

I had already done quite a bit of experimentation before I had packed it away over the summer and was expecting to be able to get it up and running quite easily. I had scoured the internet for some time as for software to drive the device with really no luck. This process is a little bit more difficult that just finding a driver for your old Epson inkjet, the 7475a is a vector graphics “printer” and thus a driver for one is quite different. There are commercial products such as winLINE, however I found them expensive and the trial prints with a large watermark.

I had been printing using the eagle CAM tool and a command line, the HPGL text file generated from eagle can be simply copied to the plotter via command prompt. I found this to be by far the best method, there are no crazy old drivers needed and the process should work regardless of operating system.

It is important to first ensure you have your serial communication settings correctly set. I have successfully used the following port settings:
Bits per second – 9600
Data bits – 8
Parity – None
Stop bits – 1
Flow control – None
The picture below also shows the corresponding dip switch settings on the plotter, now using your null modem cable that we talked about some time ago in my first post we are ready to communicate.

If you want some test HPGL code you can use some of mine, other wise fire up eagle and use the CAM tool to generate a new one. You need to make sure your generating HPGL instructions, not HPGL-2/X this thing is almost as old as me.

Once you have generated your HPGL file just open up a command prompt and navigate to the directory it was saved to. Type “copy ‘filename’ com’x'” replacing file name with whatever you saved your file as and comx with the com port you will be using, in my case this looks like “copy 4780main com3″. This will push the file to the plotter and it should start printing immediately. If it does not and the error light rapidly flashes, check your com settings again and make sure the roller lever on the plotter is engaged.

HPGL is a very simple instruction set, you can easily edit the files eagle outputs in notepad. I make use of this to delete all the “sp” instructions, I remove the pen carousel and attach a normal height permanent marker to the pen holder. we will only use the “pu” pen up, “pd” pen down, and “pa X,Y” commands there but there is a wealth of other commands in the HPGL manual.

From here on its a lot of experimentation to get the process right for you, I wanted to be able to do some SMT work. SOIC has pin spacing of 1.27mm and PLCC, and SSOP all looked like possibilities as well. Anyone who has done some PCB etching before has probably used a black sharpie for fixing little mistakes that toner transfer can have. So I first grabbed a pack of ultra fine point sharpies, that is a 0.8mm tip. I hold the pen in place by sliding a rubber grip from a mechanical pencil around the body of the marker, then simply push the pen into the plotters pen holder with the tip about 0.5″ off the surface.

The sharpie worked great as expected however I found the 0.8mm trace width too bulky to work with. After reading around some forums I found some Staedtler Lumocolor permanent markers, the small size has a 0.4mm tip and they are recommended for all surfaces. These produce a much finer trace and I as the shadow in the picture below shows will work well with SMT components. I cannot confirm this inks compatibility as etch resist just yet though.
IMGP5675 IMGP5678 IMGP5679

Sadly as of October 2008 I am having issues with my plotter, when trying to continue my experimentation I have been plagued by erratic plotting behavior. That is after following the instructions that are sent to the plotter for a few seconds it will start plotting random vectors all over the page as shown below. I have spent some time working with the plotter trying to diagnose the issue and I am coming up blank. I feel it could be my communication hardware as I am using a usb serial adapter now, and the plotter still makes great test pages.

However this project may lay dormant for some while now, I am moving on to a CNC milling process for several reasons. It would take significant modifications to the plotter to be able to use for hole drilling, a cnc process can guarantee much smaller trace width and repeatability, and because this will totally eliminate the need for FeCl or other etchants. My ultimate goal is to simplify and speed the pcb prototyping process as much as possible, I feel an all in one machine needing no chemicals is currently the best answer. I will be posting up on the beginnings of my cnc build soon.

I have enjoyed working with the 7475A and hope to revisit it with new possibilities in the future, if you have any questions or suggestions please post them.



  1. Hello, I am Bart from Belgium, and I have the same problem to plot drawings from autocad to my calcomp plotter (hp 7585b clone) through windows XP.
    the driver is only for win 95, and I tried the winline-driver that works fine, exept the big logo on the drawing. Is there a way to plot from autocad with an other driver, ore how do i try to solve this problem, When I use the standard on windows XP disk HPGL -driver it works fine until I get an error mesage on the plotter , unnown command PE ore something like that and than it stops plotting, nearly finished;

  2. I’ve been given an HP7475A by a colleague. A souvenir from a project that we both worked on 20+ years ago.

    Alas, the plotter won’t complete the self-test routine (the one that you get if you hold down both the [P1] and [P2] keys while switching it on). It looks as if the follwer drive rollers have got flat sections where it’s been stored all these years.

    Long shot – but does anyone know where I can get spares for these?

  3. I had the same problem with a USB Serial Port. I dumped the output to a HPGL file. I then ran it through a little python script that stripped some invalid commands out, inserted a 5 second timer after pen changes, a .5 second timer after PUs, and lastly wait .03 seconds between commands. I also took long strings of PAs and broke them up.

    After this, the plots came out perfect. I think it might have to do with CTS/RTS.

  4. Flow control mismatch is the source of the erratic pen behavior.

    Check the HP documentation available from http://www.hpmuseum.com for the connection cable requirements, but if you have a null-modem serial cable connection, use Xon/Xoff handshake.

    Have fun

  5. it definitly the serial buffer, most of serial usb connectors seem to be unable to use cts/rts.
    I did it somehow like BQ described it: set breaks in the serial stream for not overloading the serial buffer in the plotter.

    If someone finds a working usb serial id be glad!


  6. I just bought a 7475a. I use it on a Linux system. Your info helped me a lot. I had also problems with plotting rubbish. But I solved it. I made the original null modem cable like the partnummer of HP is (25-9P), I use a dB9 to usb adapter. I reroute a usb port to a s serial one (by STTY command). The solution to buffersize ect like mentioned here was simple. I used the CTS/RTS lines So I had not taken them together like you did. The comport had that also activated. Now I use CAM in eagle or the plotfunction in KICAD. The output from that is a file. In a terminal I copy the file to ttyUSB0 and the plotter starts to plot like he should. I do not have to alter the files or cut them in pieces. In eagle I select the right pen color so I do not have to change that to. The header files are also correct if you put the penvelocity in CAM on 36 and the thicknes at 0.3mm (if your pen is like that)

    I think the main problem people are having is because of the cable. I found about 10 different discriptions but took the one from HP (found it on the HP site or the museum site, i forgot but just look up the number in the manual and find it with google)
    he second thing is not configuring the comport for CTS/RTS

    Hope someone is helped with this info. Took me a whole day to get it goinig and because the best info I found on your site I place it here to. On my site pa4tim.nl I will place it later in more detail if I have finnished step to. Find the right ink, modify the penholder and find a way to place small PCB’s (I use it for SMD)

    Second step will be an experiment with a laserburner head and burn away a layer of etsch resistant paint (because I think burning away the copper (and not the PCB) will need to much power and will be not very easy

    Fred, PA4TIM

  7. check out some of the problems that ham radio operators have with rig control using usb to rs232 converters. you are on the right track with the rts cts not getting through. in my ham radio stuff i need the rst high to get my radio to key up and some converters are software only and do not have control voltages
    hope this helps

  8. Good site! I really love how it is easy on my eyes and the data are well written. I am wondering how I might be notified whenever a new post has been made. I’ve subscribed to your RSS feed which must do the trick! Have a great day!

  9. Hi, I wanted to plot layout from Protel 99 SE directly on film or PCB, with my
    Windows drivers are not good because they are clogging pen very
    quickly (their output is quite chaotic with many penups and downs which
    produces un-acceptable results.. if they work at all).
    Long time ago, I used a custom-written driver (for Ultiboard, DOS version.. I still have the Pascal source code) which produced beautiful plots (pads first, spiralling inwards with pen width compensation and leaving holes for drill guiding) and lines were started after the pads dried out – no pen clogging.
    Unfortunately, this package (Ultiboard for DOS) is pretty basic for today’s standards..
    Protel PCB design files (saved in text format) could be used to convert into HPGL.. I started this job some time ago (code was written in Pascal as well).
    Now I can see that there are still people using (or trying to use) pen plotters, so I am trying again to get some help (or help someone).
    Thanks in advance,

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  12. Hello, great tutorial. I have the same plotter and tried to set it up to draw pcbs according to your instructions but when I try to copy the file to the plotter it doesn’t start plotting and only the error light is flashing. I have checked my com settings and the plotter dip switch is as in your picture. What could be the problem? Could you send me a test HPGL file so I could find out if the problem is in the files I made?

  13. Well now I got it to work. I used the windows “add printer” wizard and installed windows drivers, then it worked but for some reason it stopped plotting in the middle of the pcb every time, then I played with the com settings and set the “flow control” to “hardware” and now it works like a charm. Thanks for this blog again

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  15. Bojan,
    Have you been able to recreate your driver for HPGL that creates crisp clean pads? The drives I have, like you mentioned, keep slamming the pen down and create a mess of the pads and holes are not even visible. I would love to see what you have done. Thanks.

  16. I just ran on to this site, and it has been awhile since I’ve used my 7475a plotter, but I’ll give you what info. that I can.

    For the cable, get one from here :

    The 7475a requires requires HPGL and will not work with HPGL2. The drivers that are used in Autocad (using Autocad setup) will work, but you cannot use the plotter as a system printer/plotter because windows uses HPGL2.
    For the drivers to use for Windows (Ive used these with XP, and I think that I’ve used them Win 7). You have to use Roland DXY1100 ??? drivers. I can’t seem to find the drivers right now on the net, but what you are looking for is a file Roland RWD-028.

    The dip switch setting on the back of the plotter (looking from the front, reading right to left)(starting with S1 and ending with B1) should be :


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  26. I have an old Dec version of the HP 7475A. Is anyone interested in it before I toss it out. I have a bunch of pens…


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  28. que tal amigos quiero contribuir con la experiencia en un hp7475A . tenia el problema que le mandaba a imprimir y solo lo hacia en parte y se quedaba la plumilla casi junto al carrusel de las plumillas completamente detenidas y hasta ahí llegaba . después de mucho experimentar con programas de cad llegue al resultado que con el pcb wizard y con una configuración de los pines S1=1 S2=0 D=0 A4=1 y la velocidad de 1200 baudios B4=0 B3=1 B2=1 B1=1 0111 queda como sigue viendo de atrás al frente ” 100100111″ . ya con esto funciona a la perfección e imprime todos los PCB por grandes que fueran . las plumillas adapte unos sharpies . ojala y mis comentarios les sean utiles si los puedo ayudar de alguna otra manera puedes cominicarse a mi correo joany@terra.com.mx

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  30. Hello

    I have an old HP 7475 and now I am under Vista Or windows 7 do you think that it’s possible to use this machine with :
    1) Windows vista or seven
    2) with an adaptator RS232 (DB25 com ) —-> USB
    3) is there a driver for that ( winline or other ) and is the driver 100% operational

    Thanks for your feedback

    Best regards

    Michel from France

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  32. I just wanted to let you know that I got my 7475A up and running thanks to your documentation here. I was able to do it by using the driver provided from the WinLine company, your information gave me the correct dip switch settings and by using a null modem cable that all did the trick. Thank you so much for sharing. Also I thought I should mention that i did try the Roland drivers that some others have mentioned using and I was unsuccessful with that, thats why I am using the winline driver at least until I come up with something else.

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