28158 Parallax Inc, 28158 Datasheet - Page 5

• Manufacturer Part Number: 28158
• Description: BOARD HOMEWORK BASIC STAMP(10PK)
• Manufacturer: Parallax Inc
• Series: BASIC Stamp® 2r
• Type: BASIC Stamp Kitr

Specifications of 28158

• Contents: Development Board
• Product: Microcontroller Accessories
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With/related Products: BASIC Stamp® 2 and Board of Education
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

Power Consumption and Battery Life
Parallax normally designs BASIC Stamp carrier 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 a 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 a Running Indicator LED to the “clock” line of the BASIC Stamp 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 Running Indicator LED is a low current LED consuming only about 2 mA.
If the BASIC Stamp is being used in a project where at least some small amount of time is spent doing nothing
you can put it in a low-power mode to extend battery life using the SLEEP command (Table 2). The duration
which you put the BASIC Stamp to SLEEP is accurate to ± 1% at 75° F and can range from 2.3 seconds to 18
hours (you can “wake up” and go back to sleep after 18 hours). By comparison, the PAUSE command is simply a
delay in a PBASIC program yet the BASIC Stamp continues to draw full operating current. See the BASIC Stamp
Windows Editor on-line help for all the details on the SLEEP and PAUSE commands.
Maybe putting a BASIC Stamp to SLEEP permanently only demonstrates that a 9V battery can last almost two
years if you wake the BASIC Stamp once in a while. In reality, projects need to wake up and provide current to
“loads” like LEDs and other chips used in your project. If you know the current draw of the individual
components and how long they are activated you can make an educated guess at total current consumption and
battery life. If you’re only visiting your North Pole weather station annually even a small battery can provide a
long lifespan for the BASIC Stamp, not to mention larger batteries with more milliamp hours.
To clarify the different power consumption operating scenarios and their effects on battery life review the
following two programs in conjunction with Table 2.
Both example programs below have the same result. The BASIC Stamp will send numbers to the BASIC Stamp
Editor's Debug Terminal and then go into a period of inactivity for one second. With the PAUSE example the
Running Indicator LED remains on because the EEPROM is still communicating with the BASIC Stamp interpreter
chip, but with the SLEEP example the EEPROM is shut down and the Running Indicator LED is off.
Copyright © Parallax, Inc.
BASIC Stamp 2
and Power LED
during different
Table 2
current draw
operation.
modes of
Milliamp hours is a statistic measuring the amount of energy stored in a battery. For example, if you have a 1
mA-hr battery and a project drawing 0.5 milliamps, the battery will last for two hours. A typical 9V Duracell
alkaline transistor battery provides about 565 milliamp hours of energy.
Note: 1 mA is 1/1,000
PAUSE Mode
SLEEP Mode
#28158 BASIC Stamp HomeWork Board v1.3 1/10/2007
th
BASIC Stamp
Current Draw
of an Amp. 1 microAmp (µA) is 1/10,000
40 µA
8 mA
Current Draw
Power LED
2 mA
0 mA
th
(565 mAh/(40 µA/1000 mA) = 14,125 hours
of an Amp.
Possible Battery Life
(565 mAh/10 mA)
= 56.5 hours
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