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Eric Taseski, Yihe Huang, Ronak Mehta H-Bridges and Stepper Motors 2

Standard DC Motors Speed determined by voltage level. Motor Vcc 3 GND

Stopping No movement, holds position. 4 Motor Vcc GND STOP

Free Spinning Disconnected, does whatever it wants. 5 Motor Vcc GND

What if you want precision? 6

Stepper Motors! Precision movement via stepping Can count revolutions Can rotate continuously unlike a standard servo 7

How Stepper Motors Work Divides a full rotation into a number of steps. Move one ‘step’ at a time. 8

Stepper Motors 1. The horizontal pair is driven with power in one direction. This pulls the oppositely polarized teeth to align with them. 2. The horizontal pair is de-energized, and the vertical pair is energized. 3. The vertical pair is de- energized, and the horizontal pair is energized in the opposite direction. 4. The horizontal pair is de- energized, and the vertical pair is energized in the opposite direction. 9

How Stepper Motors Work 10

Stepper Modes: Wave Mode A B C D (codeproject.com) 11

Stepper Modes: Full Step Mode 12 A B C D (codeproject.com)

Stepper Modes: Half Step Mode 13 A B C D (codeproject.com)

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Stepper Motors Contd. 15

How do we power them? 16

H-Bridges! Allows low voltage logic while driving external power to motors. Easily control current in both directions, allowing motors to move forwards and backwards. Useful for DC motors, stepper motors, servos, solenoids, etc. 17

H-Bridges Each half bridge is a transistor with an enable. LOW Voltage Input Control Logic HIGH Voltage Output Motor Voltage Logic Enable Motor Logic Input 18

H-Bridges 19 EN 1,2 EN 3,4 Input 1 Input 2 Input 3 Input 4 Output 1 Output 2 Output 3 Output 4 Vcc, Motor Supply Voltage GND

H-Bridge Pinout -EN pins enable output (1 EN pin per pair) -A’s are control inputs -Y’s are outputs -Vcc1 is circuit logic voltage -Vcc2 is the motor supply -Grounds go to ground 20

Full-Bridge with DC Motor 21 Motor + - Enable Input A Input B ENABLEInput AInput BResult 110Motor turns CW 101Motor turns CCW 10 or 1 Fast Stop 00 or 1 Free Spin

How to wire up a stepper motor and the L293D Left side can be adapted to our SmartFusion kits. (codeproject.com) 22

Protips #1-4 1.Heatsinks, or drive low to all pins to not drive current 2.Non-negligible voltage drop across H-Bridge 3.Varying PWM Duty Cycles can be used on ENABLE to control voltage supplied (speed control) 4.Frequency response of motor Low PWM frequencies may create audible buzz or hum High PWM frequencies waste power 23

References L293D explanation with Stepper Motor details: Stepper motor configurations with microcontroller pins: Microstepping (not covered): Different types of stepper motors explained: Stepper wikipedia page: H-Bridge wikipedia page: Adafruit stepper with arduino tutorial: L293D Datasheet: 24

Backup Slides 25

H-Bridge with DC Motor S1S2S3S4Result 1001Move CW 0110Move CCW 0000Free Spin 0101Brake Shoot-through

Microstepping Half stepping with sinusoidal transitions between steps allowing theoretically infinitesimally small step sizes. 27