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YZ TABLE WITH STEPPER MOTOR CONTROL Part.4: Motor Control Boards This month, we describe the modified motor controller boards for the XYZ Table. The new controller boards include the motor voltage interlock circuit described in the May 1999 issue, to prevent possible damage to the driver transistors. By RICK WALTERS The operation of the stepper motor controller cards was first covered in the August and September 1997 issues. There are two boards involved: (1) a single controller which controls the Z-axis stepper motor; and (2) a dual controller which drives the X and Y stepper motors. All motors are driven under software control from the PC. For the sake of completeness, we shall briefly cover these items again, especially for those who may not have the relevant issues to hand. Fig.21 shows the circuit for the single con­ troller, while Fig.22 shows the dual controller. As can be seen, the front ends of the two circuits are identical. It’s only the output stages following IC2 that differ. The data input to all cards is from the parallel port of a PC via the Port A data lines D0-D7. These are the signals that would normally determine the character that would be printed by a printer. In this application, they determine which motor will step and in which direction. The Port C lines, C0-C3, are used to select which card ac­cepts the Port A information. As there can be up to eight differ­ent cards in a system, each card’s address is selected by a jumper C1-C8. We set the jumper to select card 2 for the dual stepper driver and card 3 for the single stepper. Let’s look at this in a little more detail. IC1, a 74HC137 one-of-eight active low decoder, is used as the address latch. This IC looks at the BCD address data on its A, B & C inputs and pulls the corresponding decimal output (Y0-Y7) low. However, this can only happen when the strobe goes Fig.21 (facing page): this is the circuit for the single motor controller. IC1 is the card select circuitry, while IC2 latches the data on the parallel port of the PC and drives the stepper motor via two H-bridge transistor circuits (Q1-Q12). 60  Silicon Chip AUGUST 1999  61 62  Silicon Chip Fig.22: the dual motor controller is similar to the single controller. In this case, however, the 8-bit latch (IC2) drives four H-bridge transistor circuits to control two motors. high and thus the output from inverter stage IC4b goes low. This momentarily pulls the latch enable (LE) input of IC1 low via the series .001µF capacitor. As a result, the card will be addressed if the decoded output is selected by the address link. In that case, the decoded low will be fed to pin 2 of IC4a and to the cathode of D1. When the strobe signal goes low, pin 3 of IC4a goes low and pin 1 momentarily pulls the LE input (pin 11) of IC2 high. IC2 is a 74HC573 8-bit data latch. When its LE input is taken high, it latches the data fed to its D0-D7 inputs from Port A of the parallel port. This data is transferred through to IC2’s Q outputs and is used to drive the stepper motor coils via tran­sistor driver circuits. The LE signal then goes low 47ms later (as set by the 47kΩ pull-down resistor), so that the data remains latched until the next strobe signal arrives. In the case of the single controller, two transistor H-bridge circuits are used to drive the coils in the Z-axis stepper motor (MA & MB). Similarly, the dual controller uses four H-bridge circuits to drive the X-axis and Y-axis stepper motors. D1, IC3c and LED1 form a card selected indicator. Normally, pins 8 & 9 of IC4c are pulled high via a 10MΩ resistor and so pin 10 is low and LED1 is off. When a valid address is received, pins 8 & 9 of IC4c are pulled low via D1. As a result, pin 10 switches high and LED1 lights to show that the card has been selected. The associated 0.1µF capacitor ensures that the LED remains on for at least one second. Motor interlock circuit IC3 and its associated circuitry forms the motor interlock circuit. Its job is to switch the V+ supply to the output tran­sistors only after the software has set all IC2’s outputs low. This is to prevent the driver transistors from turning on in random fashion at power up, which could cause one of more tran­sistors to self-destruct. The circuit works like this: at Parts List Single Stepper Motor Card 1 PC board, code 07208992, 120 x 112mm 1 DB25 PC mounting right angle male connector 1 8-way x 2 pin strip 1 jumper for above 1 3-way terminal block (5.08mm pitch) 1 SPDT relay Jaycar SY4066 (or equivalent) Semiconductors 1 74HC137 decoder (IC1) 1 74HC573 8-bit latch (IC2) 1 74HC112 dual JK flipflop (IC3) 1 74HC02 quad NOR gate (IC4) 4 BD680/682 PNP Darlington transistors (Q1, Q2, Q7, Q8) 4 BD679/681 NPN Darlington transistors (Q3, Q4, Q9, Q10) 4 BC548 NPN transistors (Q5, Q6, Q11, Q12) 1 BC338 NPN transistor (Q13) 4 1N914 small signal silicon diodes (D1-D4) 1 5mm red LED (LED1) Capacitors 2 100µF 25VW PC electrolytic 2 0.1µF MKT polycarbonate 2 0.1µF monolithic ceramic 2 .001µF MKT polycarbonate Resistors (0.25W, 1%) 1 10MΩ 4 2.2kΩ 1 1MΩ 1 1kΩ 1 47kΩ 1 470Ω 9 10kΩ 1 74HC112 dual JK flip flop (IC3) 1 74HC02 quad NOR gate (IC4) 8 BD680/682 PNP Darlington transistors (Q1, Q2, Q11-14, Q23, Q24) 8 BD679/681 NPN Darlington transistors (Q3, Q4, Q9, Q10, Q15, Q16, Q21, Q22) 8 BC548 NPN transistors (Q5, Q6, Q7, Q8, Q17-20) 1 BC338 NPN transistor (Q25) 4 1N914 small signal silicon diodes (D1-D4) 1 5mm red LED (LED1) Capacitors 2 100µF 25VW PC electrolytic 2 0.1µF MKT polycarbonate 2 0.1µF monolithic ceramic 2 .001µF MKT polycarbonate Resistors (0.25W, 1%) 1 10MΩ 8 2.2kΩ 1 1MΩ 1 1kΩ 1 47kΩ 1 470Ω 9 10kΩ Heatsink parts (optional) 1 aluminium bar 110 x 6 x 3mm 16 TO-220 insulating washers 8 3mm x 15mm bolts 8 3mm nuts 16 3mm flat washers Case Assembly 1 PC board, code 07208991, 120 x 112mm 1 DB25 PC mounting right angle male connector 1 8-way x 2 pin strip 1 jumper for above 1 3-way terminal block (5.08mm pitch) 1 SPDT relay, Jaycar SY4066 (or equivalent) 1 plastic case, 155 x 65 x 160mm, DSE H2508 (or equival­ent) 2 25-pin “D” IDC female connectors Jaycar PS0846 (or equivalent) 1 25-pin “D” IDC male connector Jaycar PP0842 (or equivalent) 1M 26-way IDC cable, Jaycar WM4504 or equivalent (one strand to be peeled off) 1 12-way terminal strip 1 4-way terminal strip mounting nuts & bolts for terminal strips 2 3mm x 10mm countersunk bolts 2 3mm x 6mm bolts 2 3mm x 25mm threaded spacers Semiconductors 1 74HC137 decoder (IC1) 1 74HC573 8-bit latch (IC2) Miscellaneous Hookup wire, tinned copper wire (for links). Dual Stepper Motor Card switch on, both flipflops in IC4 are reset by the 1MΩ resistor and the 0.1µF capacitor con­nected to pins 14 & 15. This means that both Q outputs (pins 5 & 9) are low and so the base of Q13 (Q25) is held low via D2 & D3. AUGUST 1999  63 The transistor will therefore be off and so RLY1 is also off and no power is switched through to the driver transistors. When the software is run, it first sets all the Port A outputs low. It then selects the dual motor card and so all IC2’s outputs on this card also go low. Next, it selects the single motor card, again taking its IC2 outputs low. This ensures that the motor windings will be de-energised when the relay is ener­gised. The software then takes pin 9 of IC1 low then high, which clocks IC3b on both cards. It then does the same for pin 7 which clocks IC3a. As each flipflop is clocked, its Q output goes high. When both outputs are high, the base of Q13 (Q25) is pulled high via a 1kΩ resistor. Q13 (Q25) now turns on and energises RLY1 which feeds the V+ supply to the output drivers on both cards. The main program is then executed. Card selection Fig.23: follow this parts layout diagram to build the single motor controller. The completed board is shown below, mounted in the case. 64  Silicon Chip The card selection is done by applying the correct code for the card to PORT C: C1-bar, C2, C3-bar and C4-bar. The addresses are shown in Table 1. The convoluted numbering is due to three of these inputs having inverted logic (a high in the program outputs a low on the Port C pin). Thus, to select card 2, the value 9+STH (OUT PORTC, CARD# + STH) is placed on PORT C (see the program listing). STH (STrobe High) is defined as -1, so the actual value placed on PORT C is 8 (9-1). Because strobe line C0-bar is also inverted, this effectively takes C0-bar and C1-bar high and the other two lines low. If IC4b’s inputs go high, its output (pin 4) goes low. This momentarily pulls pin 4 of IC1 low via a .001µF capacitor. IC1 then decodes the input levels (eg, A high = Y1 low, B high = Y2 low & C high = Y4 low) and switches the decoded output (Y1 in this case) low. As soon as the .001µF capacitor charges, pin 4 goes high again and the input data can be altered without the output changing. The next line in the listing is OUT PORTC, CARD# + STL and if you follow the logic, C0-bar will go low, pin 4 of IC4b will go high and pin 3 of IC4a will go low. If the card selector link is in the C2 position, pin 2 of IC4a will also go low. Pin 1 of Tabl e 1: Card Addresses Card 1 11 Card 2 9 Card 3 15 Card 4 13 Card 5 3 Card 6 1 Card 7 7 Card 8 5 IC4a will thus momentarily pull the latch enable (LE) input of IC2 high via a .001µF capacitor and the data on PORT A will be transferred and stored on the Q outputs, as described previously. Obviously, if the link selects a different card, the data on the inputs of IC2 will not be transferred to the Q outputs. By putting high and low logic levels on the various inputs, we can therefore energise or de-energise the MA and MB motor windings and determine the direction of the current through the windings. Construction Fig.23 shows the assembly details for the single motor control card, while Fig.24 shows the details for the dual con­troller. Install the parts on the two boards as shown, taking care to ensure that all semiconductors and electrolytic capaci­tors are correctly oriented. Don’t mount the LEDs directly on the boards though. In­ stead, these Fig.24: the parts layout for the dual motor controller. Power transistors Q1-Q24 are all bolted to an aluminium heatsink – see text. should be connected via 120mm-long flying leads, so that the LEDs can later be mounted on the front panel of the case. Be careful when fitting the transistors, as two different TO-126 types are used. Note particularly that the transistors don’t all face in the same direction so be sure to orient the metal tabs of the transistors as shown on the layout diagrams. The 16 TO-126 power transistors Fig.25: this diagram shows the drilling details for the aluminium heatsink that’s used for the power transistors on the dual controller card. The heatsink is cut from 12 x 6mm aluminium bar and is 111mm long. AUGUST 1999  65 The dual controller card is attached to the base of the case, while the single controller is mounted above it on 25mm threaded spacers. on the dual controller card are bolted to a common heatsink. This can be cut from 6 x 12mm square-section aluminium rod and should be 111mm long. Fig.25 shows the drilling details for the heatsink. Note that the transistors must all be isolated from the heatsink using insulating washers. Smear all mating surfaces with heatsink compound if you are using mica washers. No heatsink compound is necessary if you are using silicon impregnated insu­lators. The best procedure is to loosely attach all the transistors to the heatsink before fitting the entire assembly to the PC board. The BD682 PNP transistors are all mounted on one side of the heatsink and the BD679 NPN types on the other. After The rear panel carries a 12-way terminal block for the motor connections, plus a 4-way terminal block for the power supply connections. 66  Silicon Chip ELECTRONIC COMPONENTS & ACCESSORIES •  RESELLER FOR MAJOR KIT RETAILERS •  PROTOTYPING EQUIPMENT •  CB RADIO SALES AND ACCESSORIES •  FULL ON-SITE SERVICE AND REPAIR FACILITIES •  LARGE RANGE OF Ph (03) 9723 3860 Fax (03) 9725 9443 Come In & See Our New Store M W OR A EL D IL C ER O M E ELECTRONIC DISPOSALS (COME IN AND BROWSE) Truscott’s ELECTRONIC WORLD Pty Ltd ACN 069 935 397 27 The Mall, South Croydon, Vic 3136 email: truscott<at>acepia.net.au www.electronicworld.aus.as P.C.B. Makers ! If you need: •  P.C.B. High Speed Drill •  P.C.B. Guillotine •  P.C.B. Material – Negative or Positive acting •  Light Box – Single or Double Sided – Large or Small •  Etch Tank – Bubble or Circulating – Large or Small •  U.V. Sensitive film for Negatives •  Electronic Components and •  •  Fig.26: the external wiring details for the two controller cards. The card select jumpers are set to C2 for the dual controller and C3 for the single controller. mounting them, use a multimeter (set to a high ohms range) to confirm their collectors are all isolated from the heatsink. The two controller cards were stacked (single board on top) and fitted into a small plastic instrument case. As shown in the photos, we drilled two 3mm holes in the front corners of both boards. The dual con- Equipment for TAFEs, Colleges and Schools FREE ADVICE ON ANY OF OUR PRODUCTS FROM DEDICATED PEOPLE WITH HANDS-ON EXPERIENCE Prompt and Economical Delivery KALEX 40 Wallis Ave E. Ivanhoe 3079 Ph (03) 9497 3422 FAX (03) 9499 2381 •  ALL MAJOR CREDIT CARDS ACCEPTED AUGUST 1999  67 Fig.28: this is the full-size etching pattern for the single controller card. Fig.27: here's how to make the cable that connects the controller cards to the parallel port of the PC. The two 25D female connectors are wired in parallel and must be at least 50mm apart. The red stripe of the 25-way cable goes to pin 1 of each connector. troller board was then secured to the base using countersunk head screws into 25mm spacers. The top board is secured to these two spacers at the front. The back of this board then simply rests on a piece of foam glued to the top of the heatsink on the dual controller board. Make sure that this strip of foam is correctly attached, so that the heatsink doesn’t short to any of the parts on the board above it. Fig.26 shows the case wiring details. Two insulated termi­nal strips (1 x 12-way and 1 x 4-way) are mounted on the rear panel and these terminate the wiring connections from the stepper motors and the power supply. The leads between these terminal strips and the boards should be run using medium-duty hookup wire. When the wiring is complete, attach the front panel label and drill the mounting holes for the LED bezels. The two “card selected” indicator LEDs can then be pushed into bezels from the back. Fig.27 shows the details of the cable Resistor Colour Codes         No. 1 1 1 9 8 1 1 68  Silicon Chip Value 10MΩ 1MΩ 47kΩ 10kΩ 2.2kΩ 1kΩ 470Ω 4-Band Code (1%) brown black blue brown brown black green brown yellow violet orange brown brown black orange brown red red red brown brown black red brown yellow violet brown brown 5-Band Code (1%) brown black black green brown brown black black yellow brown yellow violet black red brown brown black black red brown red red black brown brown brown black black brown brown yellow violet black black brown Software Listing 10 REM Driver software for drilling PC boards using Protel file 1140 STL = 0: STH = -1 ‘Strobe low & high 1150 PORTA = PPORT: PORTC = PORTA + 2 ‘Select parallel port 1160 OUT PORTA,0 ‘set all data lines low 1170 OUT PORTC, CARD1 + STH: OUT PORTC, CARD1 + STL ‘card1 - IC2 O/P’s low 1180 FOR PAUSE = 1 TO MDELAY: NEXT 1190 OUT PORTC, CARD2 + STH: OUT PORTC, CARD2 + STL ‘card2 - IC2 O/P’s low 1200 FOR PAUSE = 1 TO MDELAY: NEXT 1210 OUT PORTC,7 + STH: OUT PORTC,7 + STL ‘Clock IC3b 1220 FOR PAUSE = 1 TO MDELAY: NEXT 1230 OUT PORTC,5 + STH: OUT PORTC,5 + STL ‘Clock IC3a, 12V to motors 1240 FOR PAUSE = 1 TO MDELAY: NEXT 1250 OUT PORTA, 153: OUT PORTC, CARD1 + STH: OUT PORTC, CARD1 + STL ‘Home motor 1260 FOR PAUSE = 1 TO MDELAY: NEXT 1270 OUT PORTA, 105: OUT PORTC, CARD2 + STH: OUT PORTC, CARD2 + STL ‘Home motor 1280 FOR PAUSE = 1 TO MDELAY: NEXT 1290 OUT PORTA, 0: OUT PORTC, CARD1 + STH: OUT PORTC, CARD1 + STL ‘Motors off 1300 FOR PAUSE = 1 TO MDELAY: NEXT 1310 OUT PORTC, CARD2 + STH: OUT PORTC, CARD2 + STL ‘Motor off 1320 FOR PAUSE = 1 TO MDELAY: NEXT Table 2: Motor Lead Connections Lead Colour X-Motor Y-Motor Z-Motor Red 1 5 9 Bl ack 2 6 10 Green 3 7 11 White 4 8 12 that runs from the boards to the parallel port of the PC. As shown, the two 25D female connectors are wired in parallel and should be at least 50mm apart. Be sure to wire the red stripe of the 25-way cable to pin 1 of each connector. Note that you will have to buy 26-way cable and peel away one of the outside leads (not the read one). The cable exits the case through a step filed in the top of the back panel, above the 4-way connector. Connecting the motors The stepper motors used are 1.8 degree types from Oatley Electronics and these have four coloured leads: red, black, green and white. Table 2 shows how the stepper motors are wired up. As shown, the X-motor has its red lead connected to terminal 1, black to terminal 2, green to terminal 3 and white to terminal 4. Similarly, the Y-motor has its red lead connected to termi­nal 5, black to terminal 6, green to terminal 7 and white to terminal 8. The Z-motor has red to terminal 9, black to terminal Fig.29: the full-size etching pattern for the dual controller card. 10, green to terminal 11 and white to terminal 12. Next month, we will describe the power supply for the XYZ Table. We will also discuss the software drives the Z-axis motor, so that can automatically drill a board has been laid out using Protel. that you that SC AUGUST 1999  69