Elenco XP&trade - Manual (Page 53)

Project B21 24 Hour Data Logger
This circuit is a data logger, which calculates the cost
of electricity used by a lamp or other light source in one
day. You will be able to modify the program to test it
with a short time period, then restore it to the original
program to measure the energy cost over a full day.
Use the circuit from project B19 (Data Logger). Turn on
the slide switch (S1). Load the program “Data Logger
24 Hour” into the microcontroller (U21) using
instructions in project B1. Turn switch S1 off
immediately after download.
The microcontroller measures the amount of light on
the photoresistor (RP), at start and every hour for 24
hours. Data is stored and sent to the computer every 6
seconds, but can also be accessed at any time. Place
the circuit near a lamp or other electric light. Point the
photoresistor at the source to be measured and shield
it from daylight and other light sources. Turn on S1 and
test circuit. The red LED should be on for 6 seconds
then off for 6 seconds when the source is on. The green
LED will be on for 6 seconds then off for 6 seconds
when the source is off. If ambient light interferes try
using a tube from a roll of toilet paper to shield the
photoresistor (RP) from other light sources. Data can
be taken for 24 hours. When memory is full both LEDs
will blink.
You may turn off the data logger (S1) and reconnect it
to your computer at any time to inspect data gathered
thus far, but time from that hour may be lost. Access
the data using the terminal window as described in the
Data Logger project.
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Optional:
In the previous project you were
shown how to change wattage and
electric cost rate to make the data
logger match your situation.
This line sets the period of time
being stored. Note how it is 60
minutes for recording each hour.
Since the memory holds 24
recordings, the memory will hold
one day of data.
Testing at high speed can be
accomplished by changing this
number from 5994 to 1. Download
and test by placing finger over (RP)
to change from on to off. Remember
to restore this value to 5994 and
download again for 24 hour use.
Point the photoresistor at
a lamp and shield it from
other light sources.