Page 279 - Robot Builder's Bonanza

248 USING DC MOTORS

On
+5 volts

Figure 22- 13 The speed of nearly all
DC motors may be varied by changing the
Off
0 volts duty cycle (on versus off times) of its supply
voltage. The longer the on time, the faster
Period the motor will turn.

Remember: The frequency of the pulses— how many occur in a second— does not change, just
their relative on and off times. PWM frequencies of 1 kHz (1000 cycles per second) to over
G 20 kHz are commonly used, depending on the motor.
Unless you have a specification sheet from the manufacturer of the motor, you may have to
do some experimentation to arrive at the “ideal” pulse frequency to use. You want to select the
frequency that offers maximum power with minimum current draw.

Bonus Projects: Interfacing to Motor
Bridge Modules

I’ve added a number of bonus motor bridge projects to the RBB Online Support site, including
using several brands of serial motor speed controllers with the Arduino microcontroller. You’ll
find connection schematics, programming code, and parts lists.
Also included are hands- on sample code projects for using the venerable L293D, and the
L298, with the three controllers highlighted in this book: Arduino, PICAXE, and BASIC
Stamp. See Appendix A for more details about the RBB Online Support site.
The sample code demonstrates motor direction control, plus PWM speed control.

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