Page 214 ·
Robotics with the Boe-Bot
Constants can even be used to calculate other constants. Here is an example of two
constants, named
LeftThreshold
and
RightThreshold
that are calculated using the
four constants just discussed. The
LeftThreshold
and
RightThreshold
constants are
used in the program to figure out whether or not the flashlight beam has been detected.
' Average Scale factor
LeftThreshold CON Left LeftAmbient / 2 * 5 / 8
RightThreshold CON Right RightAmbient / 2 * 5 / 8
The math performed on these constants is an average, and then a scale. The average
calculation for
LeftThreshold
is
LeftBright
+
LeftAmbient
/ 2. That result is
multiplied by 5 and divided by 8. This means that
LeftThreshold
is a constant whose
value is the
5
/
8
of the average of
LeftBright
and
LeftAmbient
.
Math expressions in PBASIC are executed from left to right.
First,
LeftBright
is
added to
LeftAmbient
. This value is divided by 2. The result is then multiplied by 5 and
divided by 8.
Let’s try this:
LeftBright
+
LeftAmbient
= 20 + 108 = 128.
128 / 2 = 64.
64 * 5 = 320
320 / 8 = 40
You can use parentheses to force a calculation that is further to the right in a line of
PBASIC code to be completed first.
For example, you can rewrite this line of PBASIC
code:
pulseRight = 2 - distanceRight * 35 + 750
like this:
pulseRight = 35 * (2 – distanceRight) + 750
In this expression, 35 is multiplied by the result of (
2 – distanceRigh
t), then the
product is added to 750.
Example Program: FlashlightControlledBoeBot.bs2
√
Enter FlashlightControlledBoeBot.bs2 into the BASIC Stamp Editor.
√
Substitute your
timeLeft
measurement with no flashlight beam (from Table 6-
1) in place of the value 108 in the
LeftAmbient
CON
directive.
