Pic Controle De Motor De Passo (ingles)

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Listing 4.7

Outline of Rev Counter Program

MOTREVS Specify MCU 16F917 Include LCD function file Initialize display digits to zero Setup LCD Setup timer as external pulse counter Main loop Display 3 digits on LCD Wait for input switch on Reset counter and start motor Wait for input switch off Stop motor Convert timer count to 3 digit BCD

The timer is set up for external input using setup_timer_1(T1_EXTERNAL), and the resulting count is read using get_timer1(). The binary number obtained from the timer is divided by 2 and converted to BCD by a process of successive subtraction, which is simple if not elegant. The calculated digits are then displayed as in previous examples, using the function lcd_symbol() to output the display digits and the include file LCD.INC for the display encoding.

4.4

PICDEM Stepper Motor Control

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Stepper motor operation

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Stepper motor test program

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Speed and direction control

The main advantage of the stepper motor is that it provides position control without the feedback required by a DC motor. It has stator windings distributed around a cylindrical rotor, which has permanent or induced magnetic poles. The windings operate in groups to move the rotor by a fraction of a revolution at a time (Figure 4.8).

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N S N SN

Figure 4.9: Bipolar Permanent Magnet Stepper Motor with Two Winding sets RD7

SW2

RD6

Faster

Drive 1

CCP1 PWM1

Direction

SW3

P1

PIC 16F917

RD5

P2

P3

CCP2 PWM3 SW3 Slower

RD4

P4

Motor control logic linked for full bridge drive operation

Drive 2

Brown

Orange Rotor

Drive 3

Red

Winding Yellow

Drive 4

Figure 4.10: Stepper Motor Test System Connections

Construction The small stepper motor on the mechatronics board is an inexpensive permanent magnet (PM) type, giving 7.5 degrees per step, 48 steps per revolution. It can also be moved in half steps by suitable operation of the windings or even smaller steps (microstepping) by suitable modulation of the winding current. The motor has two bipolar windings, which means the current is reversed to change the polarity of the stator pole. The coils energize two rings of poles, creating alternating north and south poles, which interact with the permanent rotor poles (Figure 4.9). Representative windings are shown Figure 4.10; in the actual motor, coils are distributed around the whole circumference, multiplying the torque produced. Their terminals are

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connected to the four driver outputs on the board, which are normally connected for fullbridge operation. This allows the current to be reversed in the stator windings, reversing the polarity of the stator poles. The stator coils are brought out to four color-coded wires, which are connected to the driver terminals. In more expensive motors, a smaller step (typically 1.8º) can be obtained with four sets of windings. These motors usually have six wires, with a common connection for each pair of windings.

Stepper Motor Test The stepper motor is connected to the driver outputs, in clockwise order. The six driver input links must be closed to enable full-bridge operation, since the bipolar motor requires winding current in both directions. P1, P2, P3, and P4 inputs are connected to RD4, RD5, RD6, and RD7, respectively. When run, the program generates the required switching sequence on the coils to energize them in the right order. SW2/RA1 changes the direction, and SW3/RA3 and SW4/RA4 allow the step speed to be varied. Source code STEPTEST.C is shown in Listing 4.8. Only the control inputs P1, P2, P3, and P4 need to be connected to outputs RD7–RD4 at this stage. Note that the stepper motor terminal connections are not in numerical color order. As can be seen, no special program setup is needed. The program simply switches on the drivers in the order 1,4,2,3 by outputting a suitable hex code to Port D. The delay is set so that the steps can be counted visually. It is helpful to attach an indicator flag to the motor shaft, so that the stepping can be seen more easily. The number of full steps per rev can then be confirmed (48). Program STEPSPEED, Listings 4.9 and 4.10, is a development of the basic program to test the motor response to a range of step rates. The input tactile switches change the speed by modifying the delay time parameter, which is set to 16 ms by default. This gives speed of 16 ms/step  16  48  0.768 sec/rev  0.768  60  46 rpm

Direction Control The stepper motor program can now be further developed to include direction control, as shown in STEPDIR.C (Listing 4.11). The program has been restructured to incorporate

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Listing 4.8 Stepper Motor Test Program // STEPTEST.C // Test program for PICDEM Mechatronics Board stepper motor, // basic full step mode. Connect RD7-P1, RD6-P2, RD5-P3, RD4-P4 // plus all 6 jumpers for full bridge mode // Motor moves 48 steps per rev (7.5 deg/step) /////////////////////////////////////////////////// #include "16F917.h" #use delay(clock=8000000) void main() { while(1) { output_D(0x80); delay_ms(200);

//Loop always //Switch on Drive 1

output_D(0x10); delay_ms(200);

//Switch on Drive 4

output_D(0x40); delay_ms(200);

//Switch on Drive 2

output_D(0x20); delay_ms(200);

//Switch on Drive 3

} }

Listing 4.9 Outline of Stepper Motor Speed Control Program STEPSPEED Specify MCU 16F917 Set default step delay time Main loop If Direction switch pulsed, Call Forward If Direction switch pulsed, Call Reverse Forward Call Speed Output one forward cycle (4 steps) to motor Reverse Call Speed Output one reverse cycle (4 steps) to motor Speed If Up button on, halve step delay If Down button on, double step delay

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Listing 4.10 Stepper Motor Speed Control Program /////////////////////////////////////////////////////////////////////// // STEPSPEED.CMPB 22-4-07 // Program for PICDEM Mechatronics Board stepper motor, full step mode // Connect RD7-P1, RD6-P2, RD5-P3, RD4-P4 plus all 6 jumpers for full // bridge mode plus SW3-RA3 and SW4-RA4. Motor speed SW3 up SW4 down /////////////////////////////////////////////////////////////////////// #include "16F917.h" #use delay(clock=8000000) void main() { int8 time=16;

// Variable step delay

while(1) {

//Loop always //CHECK SWITCHES

if(!input(PIN_A3)) { delay_ms(10); if(time!=1)time=time/2; } while(!input(PIN_A3)){};

//Poll SW3 //Debounce //Not if min

if(!input(PIN_A4)) { delay_ms(10); if(time!=128)time=time*2; } while(!input(PIN_A4)){};

//Poll SW3 //Debounce //Not if max

//Wait switch

//Wait switch //4 STEPS CLOCKWISE

output_D(0x20); output_D(0x40); output_D(0x10); output_D(0x80);

delay_ms(time); delay_ms(time); delay_ms(time); delay_ms(time);

//Step //Step //Step //Step

1 2 3 4

} }

a procedure for modifying speed. In the main loop, the reversing button is tested; by default the motor runs forward and is reversed each time the button is pressed. Before each sequence of four steps, the speed buttons are polled and the delay modified if requested. The structure makes it easier to write the program with the right logical sequence. A flaw

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Listing 4.11 Stepper Motor Speed and Direction Control /////////////////////////////////////////////////////////////////////// // STEPDIR.C PICDEM Mechatronics Board stepper motor speed and dirc. // Connect RD7-P1, RD6-P2, RD5-P3, RD4-P4 plus all 6 jumpers(full bridge) // SW2-RA2, SW3-RA3, SW4-RA4. Motor speed SW3 up SW4 down, motor dirc SW2 /////////////////////////////////////////////////////////////////////// #include "16F917.h" #use delay(clock=8000000) int8 time=16;

//MCU select //Internal clock //Default speed

//PROCEDURES//////////////////////////////////////////////////// void speed() //Halve or double speed ////////// { if(!input(PIN_A3)) //Poll SW3 { delay_ms(10); //Debounce if(time!=1)time=time/2; //Not if min } while(!input(PIN_A3)){}; //Wait switch if(!input(PIN_A4)) { delay_ms(10); if(time!=128)time=time*2; } while(!input(PIN_A4)){};

//Poll SW3 //Debounce //Not if max //Wait switch

} void forward() //4 steps clockwise ///////////// { speed(); output_D(0x20); delay_ms(time); //Step 1 output_D(0x40); delay_ms(time); //Step 2 output_D(0x10); delay_ms(time); //Step 3 output_D(0x80); delay_ms(time); //Step 4 } void reverse() //4 steps counter-clockwise ///// { speed(); output_D(0x80); delay_ms(time); //Step 4 output_D(0x10); delay_ms(time); //Step 3 output_D(0x40); delay_ms(time); //Step 2 output_D(0x20); delay_ms(time); //Step 1 }

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void main() //Main loop/////////////////////////////////////////// { while(1) //Loop always { while(input(PIN_A2)) { forward(); } //Run forward delay_ms(10); //Debounce while(!input(PIN_A2)){}; //Wait until released while(input(PIN_A2)) { reverse(); } delay_ms(10); while(!input(PIN_A2)){};

//Run reverse //Debounce //Wait until released

} }

in the algorithm is that the program checks the buttons only after four steps, so the direction and speed do not change immediately if the motor is running at low speed. This type of problem can be solved using interrupts.

4.5

PICDEM Analog Sensors

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Light switch application

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Temperature display application

The mechatronics board is fitted with a light and temperature sensor, each of which produces an analog output in the range of 0–5 V. In common with many sensors now available, a signal conditioning amplifier is built in, so that no additional components are needed to interface with an MCU.

Light Sensor The light sensor can be tested using the analog comparator inputs of the 16F917, which allow two input voltages to be compared. An output bit in a status register is set if the positive input (C) is at a higher voltage than the negative input (C) or a reference voltage. A range of setup options are defined in the header file. The block diagram in Figure 4.11 shows the hardware configuration for this test. The connector pin LIGHT, the light sensor output, is connected to RA0 (comparator input C) and POT1 to RA3 (comparator input C), with LED D7 is assigned to RD7 to display the

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