Parallax 29157, Manual

Page: 4 / 18

Parallax, Inc. • BASIC Stamp HomeWork Board ver 1.1 Page 4
Figure 2
BASIC Stamp
HomeWork Board
Schematic
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3
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Power Consumption and Battery Life
Parallax normally designs BASIC Stamp boards with power jacks for wall transformers. Wall transformers provide
plenty of power but they are not as portable for science fairs, robots and environmental datalogging. Considering
that the BASIC Stamp draws only small amounts of current it could be deployed in a remote location and run
from a battery for a long time.
The BASIC Stamp has commands for reduced power consumption, but what about the power indicator LED? It
could drain the battery in a day or two by itself if being used to indicate a power supply! LEDs consume current,
typically 10-12 mA. Removing the LED wasn’t an option since it discloses the common technical support problem
of a missing power supply.
The solution was to connect BASIC Stamp HomeWork Board’s power LED to the “clock” line of the BASIC
Stamp’s EEPROM. The EEPROM’s clock line is active only when the BASIC Stamp is actually running a
program. Moreover, the BASIC Stamp HomeWork Board’s power LED is a low current LED consuming only
about 2 mA.