Page 189 - Anatomy of a Robot

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174 CHAPTER SEVEN
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Processor Power Draw

Some processors are simply designed for low power operation, and others are not. Don’t
even bother considering processors that do not have the types of features necessary for
low power operation. Restrict the search for a processor to suitable energy-saving
processors.

Memory Types

When selecting memory technology, pay attention to the power draw of the memory
chips themselves. In particular, some flash memory chips have a built-in energy-saving
feature. They will move to a low power state if they are not accessed within a certain
time period. This can significantly decrease power consumption with little effect on the
operating speed of the processor.

SUBSYSTEM POWER CONTROL
The robot’s subsystems should be designed with integral power control switches. The
processor, under software control, should be able to turn off the power to unused por-
tions of the robot. If, for instance, the robot will be still for a while, we may be able to
turn off all power to the actuators and motors. If the robot does not have to sense any-
thing for a while, we can turn off the sensors. A variant of this sort of power control
switch is a “dead man” power controller that will turn off subsystem power unless the
processor commands otherwise. This is useful in situations where the processor may
bomb or if the application software simply forgets to do the proper housekeeping.
Remote, unattended robots need this sort of hardware feature on subsystem power con-
trol to avoid accidentally draining the batteries.

DRAIN ON INTERROGATION

Try to use sensors that do not consume power unless they are being interrogated. For
simple digital inputs, consider using tri-stated processor inputs. Often, it’s possible to
avoid any energy drain except during the brief period where the processor is interro-
gating the input.