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Page 230 · Robotics with the Boe-Bot
Solutions
Q1. The resistance is small, a few ohms, if the light is bright. The resistance is large,
around 50 kΩ, in dim light. For light levels between bright and dim, its
resistance will be somewhere between the bright and dim values.
Q2. No. The I/O pin just quietly listens without any actual effect on the circuit. The
value of the applied voltage causes the input register to change what it stores. If
the applied voltage is less than 1.4 volts it stores a 0. Otherwise it stores a 1.
Q3. The threshold voltage is a value above which is a logic 1, below which is a logic
0. The threshold voltage of BASIC Stamp modules is 1.4 volts.
Q4. The value of Vo is determined by the ratio of the resistors. Vo changes value
because the resistor, R, changes value. R is a photoresistor which changes value
depending on the amount of light falling upon it.
Q5. It checks the sensors between each pulse, instead of having fixed maneuvers of
many pulses. This makes the Boe-Bot much more responsive.
Q6. A constant declaration tells the compiler the value of your constant.
example, MaxTemp
useful name to a number or value used in a program. To use a constant, type the
constant name anywhere in the program where the value is needed.
Q7. Expressions are evaluated from left to right. This is different than standard
algebraic evaluation, where multiplication and division are evaluated before
addition and subtraction.
Q8. In FlashLightControlledBoeBot.bs2, averages were used to calculate lighting
thresholds. In RoamingTowardTheLight.bs2, an average of the left and right
readings is calculated. They different in that the first is calculated statically in a
constant declaration, and the second is calculated dynamically as the program
runs. They are similar in that they both add two values together and divide by 2.
E1.
a) R = 10 kOhm
Vo = 5V * (2000 / (2000 + R))
= 5 * (2000 / (2000 + 10000)
= 5 * (2000 / (12000)
= 5 * ( 2 / 12 )
= 5 * ( 1 / 6 )
= 5 * 0.17
= 0.83 Volts
If R = 10 kOhm, Vo = 0.83 V
is a constant declaration. A constant gives a
CON 212
b) R = 30 kOhm
Vo = 5V * (2000 / (2000 + R))
= 5 * (2000 / (2000 + 30000)
= 5 * (2000 / (32000)
= 5 * ( 2 / 32 )
= 5 8 ( 1 / 16 )
= 5 * 0.06
= 0.31 Volts
If R = 30 kOhm, Vo = 0.31 V
For
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