Notes about step motor ROHS 28BYJ-48

1 Key parameters

• stripe angle is 5.625°/64, which means:
• the motor has a step angle of 5.625°
• the output shaft is driven by a 64:1 gear ratio.

So, for the motor to rotate 360°，it needs (360/5.625)=64 steps. For the output shaft to rotate 360°, it needs 64*64 = 4096 steps, and every step is (360/4096)=0.088°. 

Usually, we care more about the output shaft. 

• RPM is about 15 rpm
• so it runs at most (15*4096/60) = 1024 steps per second.
• Also means, one step needs at least (1/1024) = 0.98 ms. 

• Step sequences
• Step 1, Orange: 0, Yellow: 1, Pink:  1,  Blue:  1
• Step 2, Orange: 0, Yellow: 0, Pink:  1,  Blue:  1
• Step 3, Orange: 1, Yellow: 0, Pink:  1,  Blue:  1
• Step 4, Orange: 1, Yellow: 0, Pink:  0,  Blue:  1
• Step 5, Orange: 1, Yellow: 1, Pink:  0,  Blue:  1
• Step 6, Orange: 1, Yellow: 1, Pink:  0,  Blue:  0
• Step 7, Orange: 1, Yellow: 1, Pink:  1,  Blue:  0
• Step 8, Orange: 0, Yellow: 1, Pink:  1,  Blue:  0

If we connect (orange, yellow, pink, blue) to the lower 4 bits (bit:3, bit:2, bit:1, bit: 0) of a 8bits port, then the steps can be easily represented by [0x07, 0x03, 0x0B, 0x09, 0x0D, 0x0C, 0x0E, 0x06]

• Drive Voltage: 5V
• This motor needs a big current, so Arduino cannot drive it directly. Instead, usually, a ULN2003 chip works as a middle man between Arduino and the motor.

2 Example code in C

Let's assume the connection is as : 

        unsigned char steps[8] = {

                0x07, 0x03, 0x0B, 0x09, 0x0D, 0x0C, 0x0E, 0x06

        };

        DDRB |= 0xF;

        while(1){

                int i=0;

                for(i=0; i<8; i++){

                        PORTB = (PORTB & 0xF0) | steps[i];

                        _delay_ms(1);

                }

                 }

In this example, every step takes 1ms, so the motor runs 360° every (4096*1)=4096ms=4s.

3. Need a driver?

A motor driver is easy to write as long as the principle is in your mind. An important thing to consider is to use a timer-interrupt to drive the motor instead of _delay_ms(1).

I Will update when I finish one.