This document provides an overview of robotics motor drivers and DC motor control circuits. It discusses DC motor direction control using an H-bridge circuit and DC motor speed control using pulse width modulation (PWM). PWM allows modifying the duty cycle of a waveform based on a control voltage and is implemented using the 555 timer IC to control both the speed and direction of a DC motor.

1. TECHNOLOGY ROBOTICS SOCIETY Indian Institute of Technology, Kharagpur

2. A TUTORIAL ON ROBOTICS Motor Drivers

3. DC Motor Drivers These are current amplifying circuits A low current control signal is converted into a proportionally higher current signal that can drive the motor Power Transistors can switch high currents. The I Cmax is usually of the order of Amps as compared to small signal transistors which have I Cmax in mA Example: L293d, L298, ULN2003 Copyright © Robotix Team, IIT Kharagpur

4. DC Motor Direction Control H – Bridge Circuit Diagram Copyright © Robotix Team, IIT Kharagpur S 1 S 3 S 2 S 4 M 1 2 V CC Power Transistor Switches

5. H – Bridge Working Copyright © Robotix Team, IIT Kharagpur S1 S2 S3 S4 Current Direction Effect 1 0 0 1 1 to 2 Motor spins forward 0 1 1 0 2 to 1 Motor spins backward 1 1 0 0 - Braking Occurs 0 0 0 0 - Free running

6. DC Motor Speed Control Circuit Input is the operating voltage & control signal Output is a part of the operating voltage depending upon the control signal Copyright © Robotix Team, IIT Kharagpur

7. DC Motor Speed Control Cont… Controlling the current by passing it through a variable resistor is not advisable as it is extremely energy inefficient A trick is done to achieve reduced average power Power is supplied to the motor in short intermittent bursts, as explained further Copyright © Robotix Team, IIT Kharagpur

8. Duty Cycle Fundamentals

9. Duty Cycle Cont… The time period ( τ ) is the duration after the voltage waveform repeats itself Duty Cycle is the % time of τ , the voltage is equal to the operating voltage The average voltage is equal to the ‘Duty Cycle’ % of the Operating Voltage Copyright © Robotix Team, IIT Kharagpur

10. Pulse Width Modulation PWM is a technique using which we can modify the duty cycle of a waveform depending upon an input control voltage This forms the backbone of our speed control circuit It can be easily implemented using the popular multipurpose IC 555, used widely for hobby electronics Copyright © Robotix Team, IIT Kharagpur

11. Both Speed & Direction Control Copyright © Robotix Team, IIT Kharagpur