DRIVING BIPOLAR STEPPER MOTOR WITH ARDUINO + L298N

Ever removed removing stepper motors from old printers. Well, most of the stepper tors you find in the old printers are bipolar stepper motors. Bipolar stepper motors have a permanent magnet rotor and two coils in a stator at 90 degrees to each other. 

Simple bipolar stepper

Above is a simple diagram of one. In driving bipolar stepper motors equal currents are applied to both the coils. The motor is stepped by varying the direction of current in each coil. The below diagram shows the full stepping sequence of the above stepper motor by doing so

Full step sequence of a bipolar stepper motor

The above motor has a full step angle of 45 degrees. This step angle or resolution can be improve by increasing the poles on the motor. Typical step value of a bipolar motor may either be 1.8 degrees(200 steps per revolution) or 7.5 degree steps(48 steps per revolution). These could be halved by using a half- step sequence where between each step indicated above current in the coil whose current is reversed, is switched off before reversing. Hence steps can be reduced to 0.9 degree steps or 3.75.

Enough on the details, let's get onto the driving one. The motor I used was one with full step of 7.5 degree step angle. A voltage of 9v were applied to the motor while it drew a current of about 100mA during operation. I used Arduino mega 2560 which was interfaced with L298N motor controller circuit for the purpose

L298N motor driver ciruit

Diodes were used for protection from inductive load of the motor. Datasheet of L298N recommends fast diodes, so 1N4148 were used. Input pins of the L298N were connected to Digital pins of the Arduino which I have mentioned in my code below. Logic supply voltage of L298N (pin4 - Vs) was connected to +5v pin of Arduino while the ground of the circuit was connected to ground pin of Arduino in order to supply common ground for logic operations.

The next step was to program the arduino. The following code was written to drive the motor continuously in one direction

//defining connections to L298N

int input1 = 22;

int input2 = 23;

int input3 = 28;

int input4 = 29;

void setup()

{

  pinMode(input1,OUTPUT);

  pinMode(input2,OUTPUT);

  pinMode(input3,OUTPUT);

  pinMode(input4,OUTPUT);

}

void loop()

{

//1st step

digitalWrite(input1,HIGH);

digitalWrite(input2,LOW);

digitalWrite(input3,LOW);

digitalWrite(input4,HIGH);

delay(10);  //small delay between each step of 10ms

//2nd step

digitalWrite(input1,LOW);

digitalWrite(input2,HIGH);

digitalWrite(input3,LOW);

digitalWrite(input4,HIGH);

delay(10);

//3rd step

digitalWrite(input1,LOW);

digitalWrite(input2,HIGH);

digitalWrite(input3,HIGH);

digitalWrite(input4,LOW);

delay(10);

//4th step

digitalWrite(input1,HIGH);

digitalWrite(input2,LOW);

digitalWrite(input3,HIGH);

digitalWrite(input4,LOW);

delay(10);

}

Arduino was given 9v and the circuit was powered up. Ta - Dah. Here you go. Your application may vary from driving the motor continuously in one direction. Now, its all up to you to make-break this code to tune into your application. Cheers :)

Using Electronic Components #1 - 555 timer

 NE555 - Let's Emit a pulse

What is 555 timer?

   555 timer IC could be regarded as one of the most successful chips ever made. Statistics show that 555 timer IC is the world's mostly manufactured IC with over 1billion IC's still being produced each year. From hobby electronics to engineering, 555 comes in handy in enormous range of applications. If you are a starter this is probably the best IC to start with, given its simplicity and capability.


So what can 555 do? let's get started. First application will be emitting a pulse.

pinout of 555 timer

Before beginning with our experiment i will introduce each pin of 555

Vcc - positive supply pin
ground - ground pin
pin 2 - trigger pin. output triggers when voltage on pin falls below 1/3rd of supply voltage
pin 6 - threshold pin. 555 output goes low when voltage on the pin goes above     2/3rd of supply voltage
pin 4 - reset pin
pin 5 - control pin. As of now do not pay much attention to this pin as i will go through its uses in the next tutorials

Components needed:

R4: 100K
R1: 4.7K
R3: 470
R2: 10K linear potentiometer
C1: 47 μF electrolytic
C2: 0.1 μF ceramic
IC1: 555 timer
D1: 5mm LED










If you are unable to find some parts feel free to replace them with close substitutes. At this point what matters is seeing what is happening.

First make the connections as shown in the schematic above. Begin by turning the potentiometer(R8) to its maximum resistance. Then gradually reduce the resistance of R8. At some point you will observe LED light up, stays on for 5 seconds and go off. So that is it, you emitted the pulse, but what exactly went through? how can  you customize this? let me take you through it

555 output triggered when the voltage on the pin 2 of the IC fell below 1/3 of the supply voltage(in this case below 3v). It then emits a pulse whose time length depends on R4, C1 and triggers off again. 555 in this mode is called monostable mode

So what do all the resistors, capacitors around 555 do?

R1, R2 - acts as a voltage divider to change voltage on pin2

R3 - limit the current through LED

R4, C1 - controls the duration of the pulse. If you are aware of the time  constant concept you will understand duration of pulse is roughly equal to R4*C4 (time constant). Of course you will need to have a little idea of insides of 555, which is available on data sheet. And if you are unfamiliar with time constant concept just remember the result i derived

C2 - it's used to prevent any voltage fluctuations from affecting our proceedings. However it's not critical as for now

Note: You can add an electrolytic capacitor of 100uf between positive and negative supply to prevent any effect from supply voltage fluctuations

So we are done for now. You are free to customize this according to your need. Cheers :)