How to control unipolar/bipolar stepper/stepping motors such as 28BYJ48 using motor drivers such as L293D

Question

So I'm having issues with controlling the motor with this ic.

I have got it to work when it was unipolar with the uln2003.

I slit the red wire so there are only 4,two windings. Measured ohms across coils.

Pin 1 ic - 5v pos

Pin2 ic - gpio 27

Pin3 ic - yellow motor wire

Pin 4 ic - ground

Pin 5 ic - ground

Pin 6 ic - Blue motor wire

Pin 7 ic - gpio 22

Pin 8 ic - 5v pos

Pin 9 ic - 3v3 pi

Pin 10 ic - gpio 9

Pin 11 ic - pink motor wire

Pin 12 ic - ground

Pin 13 ic - ground

Pin 14 ic - orange motor wire

Pin 15 ic - gpio 10

Pin 16 ic - 5v pos

When I run:

import RPi. GPIO as GPIO 
import time

GPIO. setmode(GPIO. BCM) 
ControlPins = [27,22,10,9] 
for pin in ControlPins:
    GPIO. setup(pin, GPIO. OUT) 
    GPIO. output(pin, 0)

seq = [[1,0,0,0],[1,1,0,0],[0,1,0,0],[0,1,1,0],[0,0,1,0],[0,0,1,1],[0,0,0,1],[1,0,0,1]]

def rotate90(direction):
    if direction == 'CW':
        for i in range (128):
            for halfstep in range(4):
                GPIO. ouput(ControlPins[pin], seq[halfstep] [pin]) 

rotate90('CW') 
GPIO.cleanup()

The data sheets do not have a truth table(seq) as far as I can see. They also say to use diodes and caps(I'm assuming that's for efficiency).

The 28byj is making sounds, but isn't rotating. I think this is because of my truth table. What should it be?

Sorry for the messy question. I'm on my phone.

Answer 1

Question

Stepper 28byj48 unipolar OK with uln2003

Slit the red wire so there are only two windings

Measured ohms across coils. Pin 1 ic - 5v pos ... (OMG, 16 connection pairs!!!)

Answer

I did the same thing a long while ago. I vaguely remember I performed the following operation converting the stepper from unipolar to bipolar.

1. Open the casing

2. Cut away the red wire, so that the two windings do not electrically connected to each other.

Now I am googling something to read, and jot down some pictures, ...

Now the schematic for L293D driving a bipolar stepping motor.

I have found a L293D module in my junk box.

Now I have shrinked and merged 4 big pictures into one big picture for my small eyes to look at.

The problem is we don't know the colour code of the wiring scheme. For example, what colour is for 1a, 1b, 2a, 3b etc. If we could not find the colour code, we may need to use the multimeter and a 6 battery to find by trial and error manually.

Anyway, now I have removed the casing of the 5 wire unipolar motor. Next step is find out which trace to cut to separate the two coils sticking together at the red wire, to make it a 4 wire, two non connecting coils, red wire don't care bipolar motor.

Now I am also thinking of testing my old stepper and compare how more powerful is, comparing to the small guy. The old guy costed me US$2 (a couple of years ago). The wires were badly torn, but I know there is no contact brushes to wear, so found it good and quite. A new one costed US$25. I thought it was very good money for a hobbyist to play with and learn something. As a newbie, I needed to google hard before I know how to use a battery, a multimeter, and a 1 pole, 12 throw to figure out which wire goes with which other wire, ...

A stronger stepping motor to replace 28BYJ48, should be strong enough to turn Rubik cube

/ to continue, ...

References

(1) 28BYJ-48 - 5V Stepper Motor

(2) Stepping Motor Fundamentals - Microchip

(3) Control of Stepping Motors A Tutorial - DW Jones Uni Iowa, 1995

(4) L293x Quadruple Half-H Drivers Datasheet - TI

(5) MINI L293D DC/stepping motor controller board - ¥9.50

(6) L293D DC motor control card dual h-bridge Module - US$ 1.43

(7) Stepping Motor Tutorial (Unipolar/Bipolar, Half Step/ Full Step, ULN2003/L293D)

(8) Stepping Motor Tutorial Using L298N Driver

(9) How does a Stepper Motor work? (Youtube 6 minute video) - Learn Engineering 3.17M subscribers 2,453,537 views 2016oct19

(10) What could be the reasons for a stepper motor stuttering with an A4988 driver? - EESE 2021apr05

(11) My experiments with stepper motor - ScientistNobee, 2015mar12

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Appendices

Appendix A - Why we need a dual bridge motor driver (L293D or L298N)?

We need to use two H-bridge circuits (dual H-bridge) to drive both coils of a bipolar stepper motor.

How does a H-bridge circuit work?

The field effect transistors (FET) Q1 to Q4 act like switches. The diodes D1 to D4 act like freewheeling diodes to channel back-electromagnetic force (back-EMF) of the motor coils. When the ‘switches’ Q1 and Q4 are closed (and Q2 and Q3 are open) a conducting path is created and current will flow from +9Vdc to Q1 to the coil to Q4 to GND. By opening Q1 and Q4 switches and closing Q2 and Q3 switches, a different conducting path is generated from +9Vdc to Q2 to the coil to Q3 to GND. If you pay close attention you will notice the current flowing through the coil in the opposite direction, allowing reverse operation of the motor.

Note however the switches Q1 and Q2 should never be closed at the same time, as this would cause a short circuit. The same applies to the switches Q3 and Q4. This is why we cannot simply use Arduino [or Rpi] HIGH and LOW outputs to reverse the polarity; a H-bridge circuit is essential.

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