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YZ TABLE WITH STEPPER MOTOR CONTROL Part.5: Power Supply & Software This power supply has been specifically designed to power the controller cards and the stepper motors used in the X-Y-Z Table, as presented in last month’s issue. In addition, we show you how to drill your first PC board. By RICK WALTERS The software which controls the three motors energises the Z-axis motor continuously. Conversely, the X and Y motors have the power removed when they are not stepping. This allows us to use a 15V supply for the X and Y motor driver stages, to ensure that at least 12V is fed to the motors after the voltage drop across the driver transistors is taken into account. By contrast, the Z-axis motor driver stages are powered from a +12V rail. The resulting lower voltage applied to the Z-axis motor ensures that it doesn’t overheat during the long periods for which it may be energised. Keeping the voltage constant on the X and Y stepper motors allows us to consistently step them at their maximum speed, regardless as to whether one or both motors are driven. If the voltage varied (as it would with an unregulated supply), we would have to reduce the maximum stepping rate. Fig.30 shows the circuit of the power supply. This is simi­lar to the Stepper Power Supply described in the December 1997 issue. The previous unit provided unregulated +18V & +12V rails, along with a regulated +5V rail. The revised unit described here does away with the +18V rail and provides a regulated +15V rail instead. It also uses a larger power transformer. This was done because the output of the original supply varied quite a bit, depending on whether one, two or three motors were being driven at any given time. Circuit details The circuit is built into a standard plastic case, with binding post terminals used for the supply outputs. A LED provides power on/off indication. 72  Silicon Chip As shown in Fig.30, the 30V centre-tapped secondary of the power transformer is full-wave rectified by diodes D1 & D2. The output from the rectifiers is then filtered using a 4700µF ca­pacitor to give around 2022V, depending on the load. This rail is then fed to 3-terminal regulator REG2, which provides a +15V regulated rail to power the X-axis and Y-axis stepper motors. This adjustable regulator is rated at 3A, since the X and Y motors will draw a total current of 1.5A when they are both stepping. The output voltage can be trimmed by changing the 150Ω resistor. A 470µF capacitor and a parallel 0.1µF capacitor are used to filter the output from REG2. The second regulator, REG1, provides a stable +5V rail for the logic circuits on the controller cards. Its output is fil­ tered using 10µF and 0.1µF capacitors. This bypassing of the regulator outputs is a precaution to prevent the regulators from oscillating if we have long leads between the power supply and the controller cards and motors. The +12V rail for the Z-axis stepper motor is derived from D3. This diode half-wave rectifies the output from a 24V tap on the transformer, while a 4700µF capacitor filters the output. The unloaded output voltage is around 13.5V but this drops to around 11V as soon as the motor is energised. For this reason, the software drives this motor at a slower stepping rate than the X & Y motors, so that it operates reliably with the lower voltage. Assembly Most of the parts are mounted on a PC board coded 10108993. Fig.31(a) shows the assembly details. Fig.30: the circuit provides regulated +5V & +15V supply rails, plus an unregulated +12V rail. Begin by installing eight PC stakes at the external wiring points, then install the resistors, diodes D1-D3 and 3-terminal regulator REG1 (7805). Note that D1 & D2 are both 1N5404 types, while D3 is a 1N4004. Next, install the capacitors, taking care to ensure that the electrolytics are correctly oriented. Don’t install REG2 at this stage, as it’s not mounted directly on the board. The completed PC board is housed Fig.31(a): follow this parts layout diagram to assemble the PC board. in standard plastic case, along with the power transformer. The front panel carries four banana sockets (0V, +5V, +12V and +15V) and the power indicator LED, while the rear panel carries the cordgrip grommet, safety fuse and mains switch. Both the transformer and the PC board are mounted on an aluminium baseplate (see Fig.32), which is earthed to ensure electrical safety. Drill out all the mounting holes in the Fig.31(b): this is the full-size etching pattern for the PC board. September 1999  73 This close-up view shows the completed PC board and the front-panel wiring. Note that regulator REG2 is mounted on the copper side of the board and has its metal tab bolted to the baseplate for heatsinking – see Fig.33. Fig.32: this diagram shows the drilling details for the aluminium baseplate. 74  Silicon Chip base­plate, then mount the transformer and earth lug as shown in Fig.34. The transformer is secured using 4mm screws, nuts and lockwashers, while the earth lug is mounted using a 3mm screw nut and lockwasher. It’s also a good idea to fit a second nut to the earth lug, so that the first nut is locked into place. Make sure that this assembly is tight. Regulator REG2 is mounted on the baseplate, beneath the PC board. This is necessary to ensure adequate heat­ sinking. Fig.33 shows the mounting details for this device. It must be electri­ cally isolated from the baseplate using an insulating pad and bush. Make sure that the mounting area is smooth and free of any metal swarf (which could puncture the insulating pad) before bolting the device down. Flying leads are used to connect REG2’s terminals back to its copper tracks on the PC board. Take care to ensure that these connections are all correct (a pinout diagram for the LM317 is shown on Fig.30) and keep the leads as short as possible. It’s a good idea to use a multimeter to confirm that the metal tab of the Fig.33: the mounting details for regulator REG2. Be sure to isolate its metal tab from the baseplate using an insulating washer and bush. regulator is properly isolated from the base­ plate. This done, the PC board can be mounted on 5mm-long stand­offs and secured using 3mm screws, nuts and lockwashers. The front and rear panels of the case can now be drilled to accept the various hardware items. The front panel is best drilled after attaching the label. Four holes are required to accept the banana sockets, plus a small hole in the middle for the LED bezel. The rear panel hardware can be positioned as shown in the photos. Use a small file to carefully profile the hole for the cordgrip grommet so that it is a precise fit. A slight problem here is that the plastic end panel is a bit too thick to suit the grommet. This means that you will need to chamfer the top and bottom of the hole on the inside of the panel to make sure that the grommet locks in properly (ie, the top and bottom slots in the grommet must engage the panel). We chamfered the prototype’s panel using a Stanley knife and a small file. Take your time with this job and make sure that the grommet is a neat (tight) fit. The hole for the mains switch can be made by first drilling a series of small holes around the inside perimeter of the marked area and then knocking out the centre piece and filing the hole to shape. Once again, make sure that the mains switch is a tight fit so that it’s secured properly when pushed into the mounting hole. The baseplate assembly sits directly on four standoffs moulded into the base of the case. You will have to drill 3mm holes through the centre of each standoff, so that 3mm mounting screws can be passed through from outside the case. Once this has been done, the baseplate assembly can be mounted in position and firmly secured. Wiring Now for the internal wiring. The mains cord Fig.34: the wiring details for the Stepper Power Supply. September 1999  75 Once the mains wiring has been completed, the rear panel can be slipped into position. After that, it’s simply a matter of completing the wiring from the PC board to the front panel and to the secondary terminals of the transformer. Use medium-duty hookup wire for this job. LED1 is wired by connecting it in series with a 330Ω resis­tor across the +5V and 0V output terminals. Its cathode (K) lead must go to the 0V terminal and this lead will be adjacent to a flat surface on the LED body (it’s also the shorter of the two leads). Testing Before applying power, check your wiring carefully and use a multimeter to confirm a good connection between the transformer metalwork and the earth terminal of the mains plug. This done, attach the lid, apply power and check that the indicator LED comes on. Finally, use your multimeter to check the voltages on the front panel sockets. You should get readings of around +15V, +13.5V and +5V with respect to the 0V terminal. Modifying the original supply The rear panel carries the on/off switch, the safety fuseholder and the cord clamp grommet. Make sure that the mains cord is properly secured and that all mains wiring is installed in a professional manner. must be secure­ly clamped by the cordgrip grommet and the Active (brown) wire connected directly to the fuseholder. The Neutral (blue) lead goes directly to switch S1, while the Earth lead (green/yellow) is soldered to the earth lug on the baseplate. Make the Earth lead somewhat longer than the other two leads, so that it will be the last to come adrift if the mains cord is reefed out by brute force. The two primary leads of the power transformer go to the bottom of S1, while the remaining terminal on S1 is 76  Silicon Chip connected back to the second terminal on the fuseholder. Be sure to sleeve all terminals on the mains switch and fuseholder with heatshrink tubing. This is done by pushing a short length of heatshrink tubing over each lead before it is soldered. After soldering, the heatshrink is then pushed over the exposed terminal and shrunk down using a hot-air gun. Be sure to use 250VAC-rated cable for all mains wiring. This includes the wiring to the fuseholder and to switch S1. If you built the supply described in the December 1997 issue, the diodes, 5V regulator and capacitors can be salvaged for the new PC board. You will need to purchase the LM317 adjust­able regulator plus a few extra capacitors and the four resis­tors. Unfortunately, the old transformer doesn’t have a high enough secondary voltage and we had to use a different type. The good news is that the new transformer fits on the old baseplate and you can use the same case. Although we haven’t tested it, it may be worthwhile trying the old transformer if you already have the previous supply. We suggest that you connect the +18V rail to the LM317 input and then adjust the 150Ω resistor to give a regulated +14V output. The existing +12V output can be used for the Z-axis card. Check this voltage under load and if it is much above +12V, fit a 5W series resistor to drop the voltage to around +12V when the motor is energised. Because the motor draws 0.6A, each 1Ω of resistance will drop about 0.6V. The indicator LED can be added to the existing +5V rail, as shown in this article. Drilling A PC Board Right, all systems should now be go. You have built and tested the power supply and stepper motor driver cards and wired them to the stepper motors. The XY table is running smoothly and you are just itching to drill the PC board for your latest pro­ject. Well, hopefully, you soon will be able to. There are just a few more checks to be made before you get into the nitty gritty. We will step back a little for a moment and cover the ground for those of you who may be a little hesitant to plough ahead without guidance. First, if you have already obtained the XY table software and followed the wiring in last month’s issue, you will find that the X arrow keys move the table in the Y direction and vice versa. In the XY table software, the first four terminals at the rear are for the Y motor and the next four are for the X motor. However, for all other software the sequence is X, Y then Z. To keep all the wiring consistent, we have modified XYREAD and XYTABLE to conform to this pattern. The new files are named XYREADM and XYTABLEM (Modified) to allow you to distinguish them from the previous versions. If you wish to modify your BAS files, all you need to do is edit line 3140 in each to read FOR A = 1 TO 4: STP(A) = STX(A) * 16 + STY(A): NEXT. Now you can swap your X and Y motor connections to conform to those shown last month. Pressing R while running the XYTABLE software allows you to select the stepping rate for the motors. This is very dependent on the processor in your computer. We used a 386 for this project and running under GW Basic a value of 50 gave good results. When using the EXE files a value of 2400 gave excellent results. To get a feel for your machine, start with these values and set new X and Y values an inch larger (or smaller) and listen to the motors step. Keep increasing the value until they begin to step smoothly. You will soon know from the “clunking” noise they make when they are mis-stepping, or not stepping at all, compared to the smooth steps they make once the stepping rate value is large enough. Set the count value so that you can move over the entire table area without any problems. Remember this number as you will need it shortly. We have mentioned previously that the BAS files are too slow and would take far too long to carry out any task but they are fine for experimenting. This is especially if you wish to alter the software to suit your needs. The seven files we mentioned in the July issue were DRLSE­ TUP. BAS, DRLSETUP.EXE, DRLSETUP. FIL, DRLTEST.BAS, DRLTEST.EXE, PCBDRILL.BAS and PCBDRILL.EXE. We glossed over them briefly then, as the power supply and new driver boards were not available at that stage. We shall now describe the func­tion of each of these BAS files in a little more detail. Setting up The first (DRLSETUP) is the program to set up the drill parameters. This simply asks for the maximum X dimension for your table in inches, the maximum Y dimension again in inches, then the stepping rate. Here’s where you enter that value you had to remember. The DRLSETUP.FIL has initial values loaded which you can accept by pressing the Enter key. Next the card number (ie, jumper setting) for the dual stepper motor card is requested, followed by the card number for the single stepper card. Then you are asked whether you want to display Imperial or metric values. As we have said in a previous article, the system was actually designed for steps of one thou­sandth of an inch, as all PC board layouts are in these measure­ ments. The metric display is only a conversion of the Imperial value to the closest equivalent. The next decisions you have to make are how many fast down and slow down steps the drill should make. When a PC board is drilled, the Z axis motor moves the drill down until it is a little above the board and holds it there. When a hole is to be drilled it just makes a small movement down and up, thus drilling the hole. The initial movement is the number of fast down steps; the latter is the number of slow down steps. The sum Power Supply Parts List 1 240V-15/0/15V power transformer, DSE M1991 or equivalent 1 plastic case with plastic end panels, 190 x 100 x 80mm 4 adhesive rubber feet 1 PC board, code 10108993, 75 x 60mm 1 front panel label, 83 x 67mm 1 240VAC 2-pole mains rocker switch, Altronics S3212 (or equival­ent) 3 red panel mount banana sockets 1 black panel mount banana socket 1 cord grip grommet 1 mains lead with moulded 3-pin plug 1 M205 safety 240VAC screw type fuseholder Altronics S5992 (or equivalent) 1 500mA M205 fuse 1 solder lug 8 PC stakes 4 5mm pillars 1 3mm x 10mm bolt 4 3mm x 15mm bolt 5 3mm nuts 5 3mm star washers 4 3mm flat washers 2 4mm x 12mm bolts 2 4mm star washers 2 4mm flat washers Semiconductors 1 7805 5V regulator (REG1) 1 LM350T variable output regulator (REG2) 2 1N5401/5404 power diodes (D1,D2) 1 1N4001/4004 power diode (D3) Capacitors 2 4700µF 25VW RB electrolytic 1 470µF 25VW RB electrolytic 1 10µF 16VW RB electrolytic 2 0.1µF monolithic ceramic Resistors (1%, 0.25W) 1 1.2kΩ 1 150Ω 1 120Ω Miscellaneous Hookup wire, 12mm-diameter heat­shrink tubing, 4mm-diameter heat­sh­rink tubing. September 1999  77 Fig.35: this is the test PC board pattern included with the software. When you drill a test board following the procedure in the text, its pattern of holes should match this artwork. of these two values cannot exceed 25 as this represents half a revolution of the motor. Pick 10 and 5 for these for the moment; you will get another chance later. The penultimate question is which parallel port you wish to use. If it is your workshop machine you probably don’t have a printer connected and in this case it will be LPT1. The last (ultimate) question is whether you wish to re-drill the PC board. If you answer no, it means that you fit an 0.8mm drill and only drill all the holes to this size, then drill the larger ones by hand later. To redrill means you want all the holes drilled with the smallest size drill. The table then returns to home and asks for the next size drill to be fitted in the chuck. It then drills all these and so on, until all the holes on the board are the correct size. Calibrating the drill depths The next program, DRLTEST, is used to confirm and adjust the drill fast down and slow down settings. The values given previously were just starting values. This program moves the drill to the fast down position, then allows you to move it up or down until it sits the distance you desire above the PC board. Once this is done, it then moves the drill down the number of slow steps you set in DRLSETUP. If this is unsatisfactory you can decrease or increase the number, which moves the drill up or down to the new position. When you exit the program, the new values are saved and used in PCBDRILL. Obviously it is wise to make sure that there is no PC board in the way each time you carry out this test, as the drill will break when it hits the board unless you have the drill motor running. If you look closely at the picture on page 72 of the July 1999 issue, you will see two clamps on the drill support bar, one towards the table base and one at the other end. These allow you to readily set the stand position for plotting or drilling a PC board. We fabricated these clamps but two automotive hose clamps from the nearest auto parts outlet would be a lot cheaper. Once you get the drill in position and moving correctly, slide the clamp up to the drill support and tighten it. Next time you plan to drill a PC board you can just slide the support down until it touches the clamp, then tighten the support knob. Drilling a test board The remaining program is PCBDRILL which should indicate its purpose. If you don’t yet have Protel or are not familiar enough with it to lay out a PC board, we have included a file called LCOSW.PCB, available both from our website (www.silicon­chip.com.au) and on the floppy we supply with this software. The two files generated by Protel (LCOSW.TOL and LCOSW.TXT) are also included. 78  Silicon Chip LCOSW.PCB is just a small board 100 x 20mm with 61 holes, including 14 for an IC, which will let you play around with the program and confirm the motor stepping rate and general operation of the XYZ table. PCBDRILL asks for the name of the PC board file to drill. In this case you type LCOSW in upper or lower case. If you add the .PCB suffix it will be accepted; if you omit it, the program will add it. Computers are supposed to save us time so why should we type any more characters than necessary? You will then be asked whether you want to flip the art­work. Normally, you lay out a PC board from the top (called the laminate or component) side and that is the side you would drill from. But as we plan to plot our boards then drill them, we will be working from the copper side and this is why it will be neces­sary to flip the layout. Pressing Enter or Y will flip it, while N maintains the view from the component side. Just to make things awkward, LCOSW.PCB was drawn looking at the copper side and does not need to be flipped. If you only plan to drill boards this could be a reason to alter the software to make Enter the no flip default. You now have to set up your computer with a directory named PROTEL, then two subdirectories below this named TRAXEDIT and TRAXPLOT. The software looks for LCOSW.TXT and LCOSW.TOL in the TRAXPLOT subdirectory. If you don’t follow this setup, the software won’t work. Setting up directories All software accessing output ports (printer) directly should be run from DOS, so if you run Windows select START, SHUTDOWN, then click “Restart in MSDOS Mode” and click OK. You will be dumped in the WINDOWS directory. Then Type CD\ and press Enter, which will place you in the root directory of your hard disk. To make a directory, type MD PROTEL and press Enter, then type MD PROTEL\TRAXPLOT and press Enter. Next, type MD PROTEL\TRAXEDIT and press Enter. Now you must copy the files to the TRAXPLOT directory. Type COPY A:LCOSW.TXT C:\PROTEL\ TRAXPLOT (press Enter), then type COPY A:LCOSW.TOL C:\ PROTEL\TRAXPLOT (press Enter). This assumes you have obtained a floppy from SILICON CHIP. Alternatively, if you download the files from our website, you must also place the two LCOSW files in the TRAXPLOT subdirectory. LCOSW.PCB must be copied to the TRAXEDIT directory (COPY A:LCOSW.PCB C:\ PROTEL\ TRAXEDIT). The other seven files should be placed in the BAS directory. If you haven’t yet created one, from the root directory (where you should still be), type MD BAS (press Enter). Then COPY A:P*.* \BAS (press Enter), then COPY A:D*.* \BAS (press Enter). The messages should read 2 files copied, then 5 files copied. When you want to run the programs, load DOS as described above, then when C:\WINDOWS shows, type CD\BAS (press Enter) and you will be placed in the BAS directory, from where you can run any BASIC or EXE program. Setting up Protel Once you have laid out a PC board using Protel and saved it, you have to create the TXT and TOL files we have just talked about. To do this, change to the PROTEL TRAXPLOT directory and type TRAXPLOT. Press the spacebar to access the first menu and the FILE menu will be highlighted. Press ENTER, then use the down arrow key to move to LOAD and then press ENTER again. If the entry does not read C:\PROTEL\TRAX­EDIT\*. PCB, then type this and press ENTER. You should now see LCOSW.PCB highlighted and pressing ENTER will load this file then return you to the FILE menu. Pressing ESC will get you back to the TRAXPLOT menu. Move down to SETUP, press ENTER, then move down to NC DRILL and press ENTER again. The box should read: OUTPUT FILE : C:<at>LCOSW X OFFSET 0.000 inches Y OFFSET 0.000 inches METHOD : GENERATE TOOL TABLE C:<at>LCOSW MATCH OVERSIZE: 0 MATCH UNDERSIZE: 0. If all these entries are correct, press ESC twice to get back to the main menu. If these entries aren’t all correct, move to the line(s) with the incor­rect entry and press ENTER to allow you to edit the value. Move the cursor down to NC DRILL and press ENTER. You will be asked CONFIRM PROCEED WITH NC DRILL (press Y). The box will show: TOOL FILE GENERATED LCOSW.TOL Press any key to continue When you do this, the next message will be: DRILL FILES GENERATED C:\PROTEL\TRAXPLOT\LCOSW.DRL C:<at>LCOSW.TXT Press any key to continue Pressing a key will get you back to the main menu after which you press ENTER as FILE is highlighted, move to QUIT (press ENTER) then enter Y to exit to DOS. This probably all sounds quite daunting if you have not done it before but believe me, it is heaps easier to actually do it than to describe how to do it. In any case, the reason we supply the LCOSW files is to save you these initial hassles. By the way, if you have downloaded Easytrax or if you have Autotrax, you will have to save all the EDIT files to the PROTEL\TRAXEDIT directory and all the PLOT files to the PROTEL\TRAXPLOT directory. If you don’t do this, you won’t be able to set up the files using Protel as described above. Note also that if you have Easytrax, you should type EASYPLOT and EASYEDIT instead of TRAXPLOT and TRAXEDIT. Next month we will describe the pen holder and the software for plotting a pattern directly onto the copper of a PC board. This will allow you to make your own PC SC boards, provided you have etching facilities. September 1999  79