Page 248 · Robotics with the Boe-Bot
The command STOP is used here rather than END, since END would put the BASIC Stamp
into low power mode.
Your Turn – Testing LED Brightness
Remember to disconnect power before you make changes to a circuit. Remember
also that the same program will run again when you reconnect power, so you can pick up
right where you left off with each test.
√ Note how brightly the LED in the circuit connected to P1 is glowing with the
220 Ω resistor.
√ Replace the 220 Ω resistor connected to P1 and the right LED’s cathode with a
470 Ω resistor.
√ Note now how brightly the LED glows.
√ Repeat for a 2 kΩ resistor.
√ Repeat once more with a 4.7 kΩ resistor.
√ Replace the 4.7 kΩ resistor with the 220 Ω resistor before moving on to the next
portion of this activity.
√ Explain in your own words the relationship between LED brightness and series
resistance.
Series Resistance and IR Detection Range
We now know that less series resistance will make an LED glow more brightly. A
reasonable hypothesis would be that brighter IR LEDs can make it possible to detect
objects that are further away.
√ Open and run TestIrPairsAndIndicators.bs2 (from page 244).
√ Verify that both detectors are working properly.
Your Turn – Testing IR LED Range
√ With a ruler, measure the furthest distance from the IR LED that a sheet of paper
facing the IR LED can be detected, with the 1 kΩ resistors in place, and record
your data in Table 7-2.
√ Replace the 1 kΩ resistors that connect P2 and P8 to the IR LED anodes with 4.7
kΩ resistors.
√ Determine the furthest distance at which the same sheet of paper is detected, and
record your data.
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