What Next? 279Experiment 32: A Little Robot CartFundAmentAls
All about limit switches (continued)
Figure 5-99. The three diagrams, from top to bottom, show
three snapshots of a motor controlled by a DPDT relay and
two limit switches. When the on/off switch at bottom-right
sends power to the relay, the lower relay contacts cause the
motor to run counterclockwise until it stops itself as its arm
opens the upper limit switch.
Figure 5-100. When the on/off switch at bottom-right opens,
the relay connects its upper contacts. This causes the motor
to run clockwise until its arm opens the lower limit switch.
Limit switches avoid the overheating and possible damage
that are likely when power is delivered to a motor that is
prevented from turning.