Mandeep Singh Walia
H
ere’s a stepper motor controller bad on 89C51 microcontroller to control the rotation of a DC step-per motor in clockwi and anti-clockwi directions. The controller is simple and easy-to-construct, and can be ud in many applications including machine control and robotics for controlling the axial rotation in XY plane. A similar circuit can be added to control the rotation of the motor in either XZ or YZ plane.
Fig. 1 shows the block diagram of the stepper motor control system. The power supply ction (in Fig. 2) consists of a step-down transformer (7.5V AC, 1A), bridge rectifier (comprising diodes D1 through D4), filter capacitors (C1 and C2) and regulator IC 7805.
We have ud here an Atmel make low-power, high-performance, 8-bit CMOS microcontroller AT89C51 with 4 kB of Flash programmable and erasable read-only memory (PEROM). It has a 128x8-bit inter-nal RAM, 32 programmable input/output (I/O) lines and two 16-bit timer/counters. The on-chip
Flash allows the program memory to be reprogrammed in-system or by a conventional non-volatile memory programmer.
cainstEPPEr Motor controL usinG 89c51 MicrocontroLLErovale
s A N
I T H E O
stepper motor coils.
When transistors conduct, 5V (Vcc) is applied to the coils and the currents flow-ing through them create magnetic fields and the motor starts rotating. The magnetic field energy thus created is stored in the coils.
When transistors stop conducting, power to the coils is cut off, the magnetic field collaps and a rever voltage (called inductive kickback or back emf) is gener-ated in the coils. The back emf can be more than 100 volts. The diodes connected across the coils absorb the rever voltage spike. This voltage, if not absorbed by the diodes, may produce opposite torque and cau improper rotation of the motor and also damage the transistors. Y ou can u virtually any type of rectifier or s
witching diodes of appropriate current and rever voltage breakdown rating.
Clock and ret circuit. T wo 33pF capacitors (C4 and C5) are connected to pins 18 and 19 of the microcontroller, respectively, with an 11.059MHz piezo-electric crystal (X TAL1) across them. The
By combining a versatile 8-bit CPU with Flash on a monolithic chip, Atmel AT89C51 is a powerful, highly flexible and cost-effective solution to many embedded control applications. From traffic control equipment to input devices, computer networking products
and stepper motor controllers, 89C51 microcontrollers deliver a high performance with a choice of con-figurations and options matched to the specific needs of each application.
IC AT89C51 features:
1. 8-bit CPU with math registers A and B
2. 16-bit program counter (PC) and data pointer (DPTR)
3. 8-bit program status word (PSW)
4. 8-bit stack pointer (SP)
The control switches for the motor are connected to Ret and Port P 0.7 pins of the microcontroller.
Circuit description
Fig. 2 shows the complete circuit of the stepper motor controller . When power supply switch S1 is clod, LED1 glows to indicate the prence of power
in the circuit. Capacitor C3 connected to pin 9 (RST) provides the power-on ret to the microcontroller.
The stepper motor is connected to port pins P2.4 through P2.7 of the microcon-troller (IC2) through the motor-driver circuit consisting of four Darlington pairs comprising transis-tors BC548 and SL100 (T1-T2, T3-T4, T5-T6 and T7-T8). Coils 1 through 4 are the
Fig. 1: Block diagram of the stepper motor control system
clock frequency of the microcontroller depends on the frequency of the crystal oscillator ud. T ypically, the maximum and minimum frequencies are 1 MHz and 16 MHz, respectively, so we should u a piezoelectric crystal with a frequency in this range. The speed of the stepper motor is proportional to the frequency of the in-put puls or it is inverly proportional to the time delay between puls, which can be achieved through software by making u of instruction execution time.
The time taken by any instruction to get executed can be computed as follows:
where ‘C’ is the number of cycles an in-struction takes to execute and ‘F’ is the crystal frequency.
The crystal frequency in this circuit is 11.059 MHz, so the time taken to execute, say, ADD A, R1 (single-cycle instruction), is about one microcond (µs). U of a 6MHz crystal will bring down the instruction execution speed to to 2 µs.
you are stupidWhen power is applied, the ret input must first go high and then low. A resistor-capacitor combination (R1-C3) is ud to achieve this until the capacitor begins to charge. At a threshold of about 2.5V , the ret input reaches a low level and the mi-crocontroller begins to function normally. Ret switch (S2) allows you to ret the program without having to interrupt the power.
One major feature of 89C51 microcon-troller is the versatility built into the I/O circuits that connect the microcontroller to the outside world. Ports P0 through P3 of the microcontroller are not capable of driv-ing loads that require tens of milliamperes (mA). Logic level current, voltage and power requirement for different versions of microcontrollers are given in T able I.
Driver circuit design. The microcon-troller outputs a current of 1.7 mA. T o drive the coil of a stepper
motor requir-ing a torque of 7 kg-cm, 12V DC and 2 amp/pha, we have to u a driver circuit that amplifies the current from 1.7 mA to 3 amp.
As mentioned earlier, we have ud BC548 and SL100 as the driver transis-tors for driving a low-power rated stepper motor such as the one ud in earlier 14cm (5.5-inch) floppy drives. But for a 7 kg-cm stepper motor, a driver circuit us-ing transistors SL100 and 2N3055 would be needed to amplify the current to 2.72 amp. T ypically, SL100 and 2N3055
each
Time=
兰卡斯特大学C×12
pacific standard timeF
= 2.72 A
Since the stepper motor has four coils, we need to u four Darlington pairs.
启蒙老师英语
programming
The program is written in Asmbly lan-guage and compiled using ASM51 cross-asmbler. The listing file is given at the end of this article.
89C51 microcontroller is
programmed using Atmel’s
Flash pro-grammer.
One-step rotation of the stepper motor ud in this project equals 1.8o . When you program the motor for 200 steps, the motor makes one complete revolution, i.e. 360o . In the program, the line ‘MOV R7, #0CAH’
Fig. 3: Flow-chart of the program
has a gain (h fe ) of 40, but 2N3055 can handle larger current since it belongs to the family of power transistors. So a heat-sink is required to dissipate the heat generated.
The output gain of the Darlington pair of SL100 and 2N3055 transistors is:
A Vo = A V1 × A V2 = 40×40 = 1600
A Vo = Io/Iin = 1600
where Io is the output current and Iin is the input current of the Darlington pair.
Io = 1600×1.7 mA
defines the rotation by 202 steps. The hex number ‘0CAH’ equals the decimal number ‘202.’ However, one can change the number of steps in the program as per one’s requirement.
The step quence is defined by the line ‘MOV A, #033H.’ T able II shows the step quence for 100 steps to energi the windings of the stepper motor in clockwi and anti-clockwi directions. The rotor of the stepper motor is in a position of mini-mum reluctance and maximum flux. Thus by energising the windings (reprented by A1, A2, B1 and B2), the rotor takes the position accordingly. In the program, the instructions ‘RR A’ and ‘RL A’ are ud for clockwi and anti-clockwi,
Fig. 4: Actual-size, single-side pcB for stepper motor control system using 89c51 microcontroller
Fig. 5: component layout for the pcB
1 $MOD51
0000 2 ORG 0000H
0000 E580 3 MOV A, P0
0002 33 4 RLC A
0003 500B 5 JNC P12
6
0005 7FCA 7 MOV R7, #0CAH;
0007 7433 8 MOV A, #033H; 0009 F5A0 9 P13: MOV P2, A;
000B 23 10 RL A;
000C 111B 11 ACALL DELA Y 000E DFF9 12 DJNZ R7, P13
13
0010 7FCA 14 P12: MOV R7, #0CAH;
0012 7433 15 MOV A, #033H;
0014 F5A0 16 P11: MOV P2, A;
0016 03 17 RR A;
0017 111B 18 ACALL DELA Y
0019 DFF9 19 DJNZ R7, P11
20
21
001B 758910 22 DELA Y: MOV TMOD, #10H
001E 7B05 23 MOV R3, #05
0020 758B08 24 Z: MOV TL1, #8D
0023 758D01 25 MOV TH1, #1D
青春向上0026 D28E 26 SETB TR1
0028 308FFD 27 BACK: JNB TF1, BACK
28
002B C28E 29 CLR TR1
002D C28F 30 CLR TF1
002F DBEF 31 DJNZ R3, Z
0031 22 32 RET
33 END
VERSION 1.2k ASSEMBL Y COMPLETE, 0 ERRORS
FOUND q
respectively.俄语翻译机
S1 and S3 are toggle switches, while S2 is a tactile switch. Switch S3 interfaced to pin 32 of the microcontroller determines the direction of rotation. When the switch is opened the motor rotates in clockwi direction, and when the switch is clod the motor rotates in anti-clockwi direc-tion.
For anti-clockwi rotation of the motor, ret switch S2 is to be presd momentarily after S3 is clod (e Fig. 3). In ca you obrve an abnormal motion of the motor either in clockwi or anti-clockwi direction, pressing ret switch S2 momentarily will make the motor run smoothly.
Construction and working
初中学历怎么考大专Y ou can asmble the circuit on any gen-
eral-purpo PCB. An actual-size, single-
side PCB for the stepper motor controller is
shown in Fig. 4 and its component layout
in Fig. 5.
Mount a 40-pin IC ba for the micro-
controller on the PCB, so you can remove
the chip easily when required. Normally,
six wires of different colours (two being
red) are available for connection to the
stepper motor. The quence for connect-
ing the stepper motor coils to the driver
card is shown in Fig. 2.
After you are done with the hardware
part, asmble the program (stpb1.asm) us-
ing ASM51 asmbler. Load the hex file gener-
ated by ASM51 into a programmer and burn
it into the chip. Now put the programmed
chip on the IC ba on the PCB.
Switch on the power supply to the
circuit using switch S1. If motor rotation
is not stable, press S2 momentarily. If the
2011上海高考作文motor does not move at all, check the
connections.
Note. The source code and the relevant
files for this article have been included in
this month’s EFY-CD.
