Datasheet

Light-Sensitive Navigation with Phototransistors • Chapter 6
Robotics with the BOE Shield-Bot • 211
8. What happens when the voltage applied to an I/O pin that has been set to input is
above or below the threshold voltage?
9. If the amount of charge a capacitor stores decreases, what happens to the voltage
at its terminals?
Exercises
1. Solve for V
A3
if I = 1 mA in the circuit above.
2. Calculate the current through the resistor if V
A3
in the circuit above is 4.5 V.
3. Calculate the value of a capacitor that has been stamped 105.
4. Write an
rcTime statement that measures decay time with pin 7 and stores the
result in a variable named
tDecay.
5. Calculate what the
ndShade measurement would be if the Arduino measures
decay values of 1001 on both sides.
6. Write a
for loop that displays fifty equal sign characters in the Serial Monitor.
Projects
1. In Activity 1 the circuit, along with the HaltUnderBrightLight sketch, made the
BOE Shield-Bot stop under a light at the end of the course. What if you will only
have a limited time at a course before a competition, and you don’t know the
lighting conditions in advance? You might need to calibrate your BOE Shield-Bot
on site. A sketch that makes the piezospeaker beep repeatedly when the BOE
Shield-Bot detects bright light and stay quiet when it detects ambient light could
be useful for this task. Write and test a sketch to do this with the circuit in
Activity 1.
2. Develop an application that makes the BOE Shield-Bot roam and search for
darkness instead of light. This application should utilize the charge transfer
circuits from Building the Photosensitive Eyes on page 189.
3. Develop an application that makes the BOE Shield-Bot roam toward a bright
incandescent desk lamp in a room where the only other light sources are
fluorescent ceiling lights. The BOE Shield-Bot should be able to roam toward the
desk lamp and play a tone when it’s under it. This application should use the
charge transfer circuits from Building the Photosensitive Eyes on page 189.
Question Solutions
1. The amount of current it allows to pass into its collector and out through its base.
2. The phototransistor’s collector and emitter terminals are connected to leads.
3. The lead that’s closer to the flat spot is the emitter. The lead that’s further away
from the flat spot is the collector.
4. The wavelength of red is closer to the wavelength of infrared, so it should be
more sensitive to red.
5. V
A3
increases with more light.