APPARATUS REQUIRED:

• 8051 Trainer Kit
• Stepper Motor Interface Board

THEORY:

A motor in which the rotor is able to assume only discrete stationary angular position is a stepper motor. The rotor motion occurs in a stepwise manner from one equilibrium position to next.

The motor under our consideration uses 2 – phase scheme of operation. In this scheme, any two adjacent stator windings are energized. The switching condition for the above said scheme is shown in Table.

Clockwise

Anti – Clockwise

In order to vary the speed of the motor, the values stored in the registers R1, R2, R3 can be changed appropriately.

ALGORITHM:

1. Store the look up table address in DPTR
2. Move the count value (04) to one of the register (R0)
3. Load the control word for motor rotation in accumulator
4. Push the address in DPTR into stack
5. Load FFC0 in to DPTR.
6. Call the delay program
7. Send the control word for motor rotation to the external device.
8. Pop up the values in stack and increment it.
9. Decrement the count in R0. If zero go to next step else proceed to step 3.
10. Perform steps 1 to 9 repeatedly.

PROGRAM:

START: ORG 4100
       MOV DPTR,#4500H
       MOV R0,#04
AGAIN: MOVX A,@DPTR
       PUSH DPH
       PUSH PDL
       MOV DPTR,#FFC0H
       MOV R2, 04H
       MOV R1,#FFH
DLY1:  MOV R3, #FFH
DLY:   DJNZ R3,DLY
       DJNZ R1,DLY1
       DJNZ R2,DLY1
       MOVX @DPTR,A
       POP DPL
       POP DPH
       INC DPTR
       DJNZ R0,AGAIN
       SJMP START

DATA:

4500: 09, 05, 06, 0A

RESULT:

Thus the speed and direction of the motor were controlled using 8051 trainer kit.

The post Interface stepper motor with 8051 Trainer Kit parallel port first appeared on Student Projects.

Chopper drive circuits are also referred to as constant current drives because they generate a somewhat constant current in each winding rather than applying a constant voltage. On each new step, a very high voltage is applied to the winding initially. This causes the current in the winding to rise quickly since dI/dt = V/L where V is very large.

When the current exceeds a specified current limit, the voltage is turned off or “chopped” and when the winding current drops below the specified limit, the voltage is turned on again. In this way, the current is held relatively constant for a particular step position.
This allows driving stepper motors with higher torque and higher speed.

Steps:

1. Measure Inductance and resistance of motor coil.
2. Get time constant.
3. Choose voltage value and desired calculation for program variables.
4. Write chopping program.

Can be done using oscilloscope and step response equation on LR circuit or from stepper motor datasheet:
Put I= maximum coil current from stepper datasheet (different from Imax)
R=Rc = internal resistance of the stepper coil from stepper datasheet
L =Lc = inductance of stepper coil from stepper datasheet
Time constant ( T ) = L/R.
Put t which is the desired time to reach the step level (start of chopping)

From above we can get   Imax  then by multiplying  it with Rc we can get the desired Applied voltage Vs to reach the maximum current in time t.

Case Study:

Stepper motor has the following specifications
Max current per phase = 1A, voltage = 5.7V, Resistance per phase = 5.7
Inductance = 6.5 mH/phase

So its time constant = 1.14 msec
We put desired t=.5 msec to reach its max current instead of taking 1.14 msec It will give us Imax = 2.8164 and Vs=16 V so we will need to apply a 16 V to reach our max current per Phase in .5 msec.

Program for Chopping driver

#include <16f628.h>
#use delay ( clock=4M )

// GLOBAL VARIABLES /////////////
int steps[] = {1,2,4,8}; // motor steps
int step_ptr = 0;
int step = 0;
int desiredt = 500; // desired time to reach max current at start of every step 0.5 msec
int choppingt = 50; // chopping time = 0.1 desired time = 50 usec

// FUNCTIONS ////////////////////

// INTERRUPTS ///////////////////

#INT_TIMER0
void change_step ()
{
if ((++step_ptr) > 3)  step_ptr=0;
step = steps[step_ptr];
output_b(step);
delay_us(desiredt);
output_b(0);
delay_us(choppingt);
}

// MAIN /////////////////////////
void main()
{
// Motor terminals are connected to Port B (Unipolar Stepper Motor)
// setup interrupt timer0 to desired stepping speed let motor change step every 2msec
// if step angle = 1.8 degree, steps per revolution = 360/1.8 = 200 steps
// time per revolution = 200 * 2 msec = 0.4 sec
// rpm = 60/0.4 = 150 rpm

setup_timer_0(RTCC_INTERNAL | RTCC_DIV_16);

// put first step//
step = steps[step_ptr];
output_b(step);
delay_us(desiredt);
output_b(0);
delay_us(choppingt);

// enable interrupt/////
enable_interrupts(GLOBAL);
enable_interrupts(INT_TIMER0);

// chopping loop//

while (1)
{
// put step (apply voltage) //
output_b(step);
// wait chopping time //
delay_us(choppingt);
// clear step ////
output_b(0);
// wait chopping time//
delay_us(choppingt);
}
}

References:

–    Wikipedia.org
–    Microchip Co. application notes.

Article by – Amr Ayoub

The post Stepper Motor Chopping Driver first appeared on Student Projects.

Some photographs of this model:

Project Description:

Keyboard section:

There are six switches in this section. They are

1. Turn left.
2. Turn right.
3. Stop.
4. About turn.
5. Park left.
6. Park right.

Circuit diagram of keyboard is shown bellow.

Car section:

There are many sub sections in this section. They are

Motor:

We are using a 5V dc motor to drive the vehicle. The speed of the vehicle and its strength is controlled by the proper use of pulley. The rear wheel of the vehicle is connected to this motor through a pulley. This motor is meant for moving the vehicle both in forward and backward direction. Microcontroller (8051) controls the forward and backward movement of the vehicle in the following manner:

Here in the above circuit, T1, T2, T3, T4 are the NPN power transistor (2N3055). A0, A1, A2, A3 are the signals coming from the micro controller. With the specific combination of A0, A1, A2, A3 we can change the direction of rotation of motor as follows:

Case I: When   A0=high; A3=high; & A1=low; A2=low
The motor rotates in clockwise direction

Case II: When   A0=low; A3=low; & A1=high; A2=high
The motor rotates in anti-clockwise direction

Case III: When   A0=low; A3=low; A1=low; A2=low
The motor stops the rotation.

The post Robotic car using 8951 Microcontroller first appeared on Student Projects.

General description and system block diagram:-

The complete board consists of transformer, control circuit, keypad and stepper motor as shown in snap. The given figure shows the block diagram of project.

The circuit has inbuilt 5 V power supply so when it is connected with transformer it will give the supply to circuit and motor both. The 8 Key keypad is connected with circuit through which user can give the command to control stepper motor. The control circuit includes micro controller 89C51, indicating LEDs, and current driver chip ULN2003A. One can program the controller to control the operation of stepper motor. He can give different commands through keypad like, run clockwise, run anticlockwise, increase/decrease RPM, increase/decrease revolutions, stop motor, change the mode, etc. before we start with project it is must that we first understood the operation of unipolar stepper motor.

Unipolar stepper motor:-

In the construction of unipolar stepper motor there are four coils. One end of each coil is tide together and it gives common terminal which is always connected with positive terminal of supply. The other ends of each coil are given for interface.  Specific color code may also be given. Like in my motor orange is first coil (L1), brown is second (L2), yellow is third (L3), black is fourth (L4) and red for common terminal.

By means of controlling a stepper motor operation we can

1. Increase or decrease the RPM (speed) of it
2. Increase or decrease number of revolutions of it
3. Change its direction means rotate it clockwise or anticlockwise

To vary the RPM of motor we have to vary the PRF (Pulse Repetition Frequency). Number of applied pulses will vary number of rotations and last to change direction we have to change pulse sequence.

So all these three things just depends on applied pulses. Now there are three different modes to rotate this motor

1. Single coil excitation
2. Double coil excitation
3. Half step excitation

The table given below will give you the complete idea that how to give pulses in each mode

Note:- In half step excitation mode motor will rotate at half the specified given step resolution. Means if step resolution is 1.8 degree then in this mode it will be 0.9 degree. Step resolution means on receiving on 1 pulse motor will rotate that much degree. If step resolution is 1.8 degree then it will take 200 pulses for motor to compete 1 revolution (360 degree).

Now let me give you the specification of the stepper motor that I have used.

Max rated voltage: –    5 V
Max rated current per coil: – 0.5 Amp
Step resolution: –    1.8 degree / pulse
Max RPM: –    20 in single/double coil excitation mode and 60 in half step mode
Torque: – 1.5 Kg/cm2

RPM calculation:-

One can calculate the exact RPM at which motor will run. We know that motor needs 200 pulses to complete 1 revolution. Means if 200 pulses applied in 1 second motor will complete 1 revolution in 1 second. Now 1 rev. in 1 sec means 60 rev. in 1 minute. That will give us 60 RPM. Now 200 pulses in 1 sec means the PRF is 200 Hz. And delay will be 5 millisecond (ms). Now lets see it reverse.

*  If delay is 10 ms then PRF will be 100 Hz.
*  So 100 pulses will be given in 1 sec
*  Motor will complete 1 revolution in 2 second
*  So the RPM will be 30.

In same manner as you change delay the PRF will be changed and it will change RPM

Stepper motor control board circuit:-

The circuit consists of very few components. The major components are 7805, 89C51 and ULN2003A.

Connections:-

1. The transformer terminals are given to bridge rectifier to generate rectified DC.
2. It is filtered and given to regulator IC 7805 to generate 5 V pure DC. LED indicates supply is ON.
3. All the push button micro switches J1 to J8 are connected with port P1 as shown to form serial keyboard.
4. 12 MHz crystal is connected to oscillator terminals of 89C51 with two biasing capacitors.
5. All the LEDs are connected to port P0 as shown
6. Port P2 drives stepper motor through current driver chip ULN2003A.
7. The common terminal of motor is connected to Vcc and rest all four terminals are connected to port P2 pins in sequence through ULN chip.

Now by downloading different programs in to 89C51 we can control the operation of stepper motor. Let us see all different kind of program.

The post Stepper motor control board first appeared on Student Projects.

The same principle is applied for track switching. Considering a situation wherein an express train and a local train are traveling in opposite directions on the same track; the express train is allowed to travel on the same track and the local train has to switch on to the other track. Two sensors are placed at the either sides of the junction where the track switches. If there’s a train approaching from the other side, then another sensor placed along that direction gets activated and will send an interrupt to the controller. The interrupt service routine switches the track.  Indicator lights have been provided to avoid collisions. Here the switching operation is performed using a stepper motor. Assuming that within a certain delay, the train has passed the track is switched back to its original position, allowing the first train to pass without any interruption. This concept of track switching can be applied at 1km distance from the stations.

The project is simple to implement and subject to further improvement.

Gate Control:

Railways being the cheapest mode of transportation are preferred over all the other means .When we go through the daily newspapers we come across many railway accidents occurring at unmanned railway crossings. This is mainly due to the carelessness in manual operations or lack of workers. We, in this project has come up with a solution for the same. Using simple electronic components we have tried to automate the control of railway gates. As a train approaches the railway crossing from either side, the sensors placed at a certain distance from the gate detects the approaching train and accordingly controls the operation of the gate. Also an indicator light has been provided to alert the motorists about the approaching train.

Track Switching

Using the same principle as that for gate control, we have developed a concept of automatic track switching. Considering a situation wherein an express train and a local train are travelling in opposite directions on the same track; the express train is allowed to travel on the same track and the local train has to switch on to the other track. Indicator lights have been provided to avoid collisions .Here the switching operation is performed using a stepper motor. In practical purposes this can be achieved using electromagnets.

The post Automatic Railway Gate Control & Track Switching first appeared on Student Projects.