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YZ TABLE WITH STEPPER MOTOR CONTROL Part.6: Pen Holder & Plotting Procedure We hope you didn’t break any drills playing around with the XYZ table and the software last month. In this final article, we describe the pen holder and the plotting software. By RICK WALTERS While it may seem a bit back-tofront to have presented the article to drill a PC board before running one to plot it, the reason is quite simple. It was a much easier task for us to develop the drilling project rather than the plotting one. This month, plot it we shall. But before talking about plotting, we need to briefly discuss pens and the pen holder. One of the major problems with plotting is finding a suitable pen which will draw satisfactorily on the copper laminate. Also the ink in the pen must be waterproof to allow it to stand up to the etching process. Once we have found the pen, we need to be able to clamp it securely to ensure consistent relocation each time we fit it. The diagram of Fig.1 shows how the pen holder was made. The top lip and turned body fit neatly into the plastic drill clamps and ensure consistent location and positioning of the pen. If you use a different brand of drill stand you will quite likely have to Extract from PCBDRAW.BAS 5570 5580 5590 5600 5610 WHILE NOT EOF(2) INPUT# 2,X$,Y$ XNEW = VAL(X$): YNEW = VAL(Y$) IF RIGHT$(X$,1) < “:” THEN 5630 ‘not P (U or D) IF RIGHT$(X$,2) = “PU” THEN GOSUB 7230 ELSE IF RIGHT$(X$,2) = “PD” THE GOSUB 7130 5620 DPEN = RIGHT$(X$,2) ‘store new value 5630 WHILE XNEW <> XOLD OR YNEW <> YOLD: GOSUB 3030: WEND ’move to new X & Y position 5640 WEND 82  Silicon Chip modify the holder shape to fit your clamps. Our prototype was turned up in mild steel while the threaded insert was in brass. Software The software files we need for plotting the PC board are as follows: PCBDRAW.BAS, PCBDRAW.EXE, DRWSETUP.BAS, DRWSETUP.EXE, DRWSETUP.FIL, PENTEST.BAS and PENTEST.EXE. You will see that they follow a similar sequence to those supplied in the July issue which allowed you to drill the PC board. The first two are the programs that actually draw the PC tracks and these will be described shortly. The next two are the setup files which allow you to set the maximum X and Y co-ordinates, the motor stepping rate, the XY card address, the Z card address, the fast and slow pen down positions and select the parallel port you wish to use. All the values except for the fast and slow pen will be the same as you used in the DRLSETUP program. DRWSETUP.FIL is the file which stores these parameters and it is accessed by both PCBDRAW. BAS and PCBDRAW.EXE. The PENTEST programs work in the same manner as the DRLTEST programs described previously, allowing you to set the distance the pen sits above the PC board when it is not drawing and the amount of pressure it applies to the copper while it is actually drawing. It will most likely take you a couple of attempts to get these positions just right. Again, as with PCBDRILL, PCB­ DRAW lets Protel do most of the hard work. We use the values in the plotter file, generated by Protel, to move to the X and Y co-ordinates, then the pen up and pen down instructions to control the Z-axis motor. A small PC board called TRACKS.PCB, which consisted of a number of tracks of increasing thickness from 10 to 60 thou, was laid out as a test board then Protel was used to generate the plot file called TRACKS.PBL. This text file is listed in Table 1. Plotter file We elected to use the Roland GL1 plotter file as this plotter was the one we used at SILICON CHIP and our copy of Protel was set up for this device. After the preamble the first significant entry is PU102,102; ie, pen up then move to X102,Y102. The next entry PD102,203; says draw (pen down) a line from X102 to Y203 and so on. This line is the vertical corner mark. The pen point thickness is given to Protel as part of the setup procedure and if you trace the next few values you will see that the pen (12 thou) draws another vertical line then a diagonal line, moves in a 5 thou arc and redraws the line, ie, the track is 17 thou wide. Actually, it should be 20 thou but who’s going to argue about 3 thou? Protel suggest that you experiment with the pen width setting until you find the best value for the particular pen you are using. They actually recommend using 13 thou for a 0.3mm (11.8 thou) pen. The program continues to read through the file, lifting and lowering the pen until it finds the entry SP0; at which time it has reached the end of the useful data, so the program terminates. Creating a temporary file That is the big picture but as the saying goes, the devil is in the detail. To make things easier for the software we first open a new file called PCBDRAW.TMP, then search through the PBL file until we locate SP1;. We then move PU from the beginning of the X entry to the end; ie 102PU, then save 102PU,102 in the new file. At the same time we store the X and Y values in XBIG and YBIG. Each entry is changed in a similar manner and written to the new file. Fig.1: the pen holder details. The top lip and turned body fit neatly into the plastic drill clamps and ensure consistent location and positioning of the pen. The prototype was turned up in mild steel while the threaded insert was in brass. If the new X or Y value is bigger than the saved BIG value then it replaces that value. At the end of this subroutine if the XBIG or YBIG value exceeds the value you have allocated to the X maximum or Y maximum values in the setup program the PCBDRAW program will terminate, writing an error message on the screen indicating an out of limits condition. Assuming there is no error message the pen will then move to the fast down position, the software will read the first entry in the TMP file and (in this case) the table will move to 102,102. Why rewrite the file you may ask? There are two reasons; the first is because we had to read through the file anyway to find the maximum X and Y values. The second is because the value of PU102 in Basic is zero, but the value of 102PU is 102. Thus it is a little quicker to compute the next X and Y values and with older machines we need to save as much time as we can, although in the long run the time taken by the X and Y mechanical movements will be the limiting factor. Plotting The X and Y co-ordinates will be read and the pen moved up and down until the end of the file is reached. The computer’s speaker will then beep to alert you to this fact, the message “Drawing completed. Homing table.” will be displayed and the table will return to 0,0. The motors will then be de-energised and the TMP file will be deleted before the program closes. As with the drilling program, if any keyboard key is pressed while the program is running, the computer’s speaker will beep to acknowledge the keypress, a message to this effect will be printed at the bottom of the screen, then the pen will home and the program will terminate. If you look at the Basic listing (from October 1999  83 The photograph above shows how the pen holder goes together (note that the spring that fits over the ink reservoir is missing), while at right is the completely assembled unit. The unit is secured by the plastic drill clamps but if you use a different brand of drill stand to ours, you may have to modify the holder shape to fit your clamps. our web site or on the floppy we can supply), you will see that a lot of the code is identical or very similar to PCBDRILL. The initialisation, opening screen, X and Y axis movement, pen control and file code are identical. The plot file (PBL) structure is different to the text (TXT) file used in the drilling program and it needs different software to process it. Subroutine 5000 does this. You will note that on line 5550 we use DPEN to keep track of the pen position. PEN is a reserved word in GW Basic, and if you look at line 1030 you will see we defined words starting with D as strings, thus DPEN allows us to keep track of PU and PD (pen up and pen down) commands. So all we have to do is read through the file, moving to the X and Y positions as dictated by the file values and take the pen up or down. This is done in lines 5570 to 5640 (see panel at start of article). The software keeps looping through the six lines 5580 to 5630 until the end of the file is reached, then the program terminates as explained previously. First PC board The first PC board we plotted and drilled is shown in the accompanying photo. All the plotting and drilling defects are due to the excessive backlash in the drillstand mechanism, not the XY table. It is not a huge amount but by the time it reaches the pen tip or drill point it can be quite a few thou. Hopefully, your drill stand mech­ anism is better in this regard than the one we used. Normally, the PC board is etched before it is drilled and during the drilling process the drill tip wanders to the pad centre which has been etched away. In the present setup, the drill tip will have no guide to the pad centre and can wander a little in any direction before beginning to make the hole. We had about 25mm of the 0.8mm drill protruding from the drill chuck and this contributed to the problem. A shorter length would probably have helped. More on pens This photo shows the test PC board that we plotted and drilled. Note that the plotting and drilling defects are due to the excessive backlash in the drill stand mechanism that we used, not the XYZ table. 84  Silicon Chip Back to the pen: the only pen we found to be really usable with our Roland plotter was a refillable type, which was quite messy to use, as the ink had to be washed out and the pen cleaned thoroughly each time a plot was done. The ink is a waterproof type which comes in 22ml bottles but a bottle this size is sufficient for a great number of plots. To our disappointment, this pen proved to be unsuitable for the XYZ table as the writing speed was too slow, causing the ink to flow into blobs whenever a pad was drawn. Even when plotting long tracks the ink tended to puddle. The plot in the photograph was done with a Pentel type CVP 0.35mm tip pen. The ink in this pen is not waterproof but the photo gives an indication of the result you can expect. We are led to believe that the Pentel type CPF, which is used to plot on film, contains a waterproof ink so we are chasing one at the moment. We will publish the outcome as soon as we get hold of it and can test it. Setting up plot files Just as we set up Protel to generate drill files last month, this time we have to set it up to create the correct plot files for drawing. You did most of the difficult work last month setting up the directories. All we need to do now is to allocate the correct plotter driver to create files that can be read by our software. Load TRAXPLOT or EASYPLOT, move down to SETUP (press Enter) and move down to PLOTTER (press Enter). The type of plotter we need is ROLAND RD-GL 1. If there is a different type press Enter and either you will be presented with a list of plotters or asked for a path to where you have saved the plot files. Move down to the correct one then press Enter again. Move down to DEVICE and press Enter. Move right down to FILE and press Enter once more. If you have loaded a file it should then read DEVICE C:<at>Filename. We’re nearly there now. Move down to OPTIONS (Enter) and if type of plot reads BOTTOM LAYER you are set otherwise press Enter and select it. Lastly, move down to FLIP LAYER SETUP and ensure that they all show normal. Pressing Enter will toggle the entry. Right, all done, now keep pressing Escape until you get back to the FILE menu from whence you can exit the program. To generate a plot file you must first load TRAXPLOT then a file, move Table 1: Protel Tracks.pbl Test Plot File ∧[.<at>; 1:IN; SP; VS10; SP1; PU102,102; PD102,203; PU203,203; PD203,381,200,384,353,536,357,537,360,534,358,531,206,378, 202,377,199,380,200,384,203,381,356,533,356,540,635,540,640, 538,642,533,640,529,635,527,356,527,351,529,349,533,351,538, 356,540,356,533,635,533,641,540,819,362,822,358,822,353,819, 349,815,347,810,347,806,349,629,527,626,531,626,536,629,540, 633,542,637,542,641,540,637,536,815,358,811,353,633,531,637, 536,635,533,813,356,827,356,827,152,826,148,824,143,820,140, 815,138,810,138,806,140,802,143,799,148,799,152,799,356,799, 360,802,365,806,368,810,370,815,370,820,368,824,365,826,360, 827,356,818,356,818,152,807,152,807,356,818,356,813,356,813, 152,813,133,559,133,554,134,549,136,545,139,542,143,540,147, 539,152,540,157,542,162,545,166,549,169,554,171,559,172,813, 172,818,171,822,169,826,166,830,162,831,157,832,152,831,147, 830,143,826,139,822,136,818,134,813,133,813,142,559,142,548, 152,559,163,813,163,824,152,813,142,813,150,559,150,559,155, 813,155,813,150,813,152,559,152,542,135,364,313,361,317,358, 321,357,326,357,331,357,337,359,341,362,346,366,349,370,352, 375,354,380,355,385,354,390,353,394,351,398,347,576,170,579, 166,582,161,583,156,583,151,582,146,581,141,578,137,574,133, 570,131,565,129,560,128,555,128,550,130,546,132,542,135,546, 139,368,317,363,335,376,348,394,343,572,165,577,148,564,135, 546,139,550,144,372,321,372,339,390,339,568,161,568,144,550, 144,554,148,377,326,385,335,563,157,554,148,559,152,381,330, 559,153,559,152,381,330; PU203,102; PD102,102; PU102,508; PD102,610,203,610; PU914,610; PD1016,610,1016,508; PU1016,203; PD1016,102,914,102; SP0; SP; IN; down to PLOT, then confirm YES to CONFIRM PROCEED WITH PLOT. The message “PLOT FILE GENERATED C:<at>FILENAME.PBL Press any key to continue” will display, and upon pressing a key you will be returned to the FILE menu from whence you can exit. Running PCBDRAW will now find the PBL file and draw it. Well that wraps up this series. We hope those of you who were interested in the project will give us some feedback on your successes or otherwise and any problems you might have experienced. Free EasyTrax software The EasyTrax software is available FREE from the Protel web site (ie, protel.com.au). But note that they will not provide any support for it; you are on your own! However, after you play around with it for a while you will find it rather easy to use, as the drop down menus guide you through SC each step. October 1999  85