Proxim RangeLAN2 7920 Manual de usuario descargar pdf (Pagina 35)

Figure 12. Proxim RangeLAN2 7920

F. MOTOR CONTROL

1. Pulse Width Modulation

A pulse width modulation circuit is the standard for control of motors in the

robotics field.

a. Circuit

The PWM control circuit designed for the SMART platform is constructed

through the use of basic 555 timer chips. A basic PWM circuit can be found on the data

sheet for National Semiconductors LM555 chip. The specific circuit designed for the

SMART robot (Figure 13) uses a 555 timer to establish a base frequency. The base

frequency and a control voltage provided from the analog outputs from the BL2000 are

then fed into a 556 timer chip which performs the pulse width modulation function for

the left and right motors.

b. Calculations

For the circuit in Figure 13 where R

=10 kΩ, R

=1 kΩ and C=1 uF. The

frequency of the 555-timer output is determined by the charge and discharge time of the

capacitor attached to the trigger and threshold inputs of the chip. The period (T) is

determined by:

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Proxim RangeLAN2 7920 Manual de usuario Pagina 35