Robotics with the Boe-Bot text v2.2

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 LeftBright + LeftAmbient / 2 * 5 / 8

RightThreshold CON RightBright + 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

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 – distanceRight), 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.