Hey everyone!
So I'm learning about the BBB by using the *Bad to the Bone *book, so this
question is directed specifically at anyone who has read or used this book.
I was doing the chapter exercises for Chapter 2, and I was a little
confused.
The questions are as follows:
*14.* Develop a series of functions to turn the Blinky 602A right and left.
The *motor duty cycle*
and the *motor on time* should be passed to the function as a variable.
*15.* Equip the motor with a fourth IR sensor that looks down to the maze
floor for “land mines.”
A land mine consists of a paper strip placed in the maze floor that
obstructs a portion of
the maze. If a land mine is detected, the robot must deactivate it by
rotating three times and
flashing a large LED while rotating
The original code given was the following:
//***********************************************************************
var b = require(’bonescript’);
//Old bonescript defines ’bone’ globally
var pins = (typeof bone != ’undefined’) ? bone : b.bone.pins;
var left_IR_sensor = pins.P9_39; //analog input for left IR sensor
var center_IR_sensor = pins.P9_40; //analog input for center IR sensor
var right_IR_sensor = pins.P9_37; //analog input for right IR sensor
var left_motor_pin = pins.P9_14; //PWM pin for left motor
var right_motor_pin = pins.P9_16; //PWM pin for right motor
var left_sensor_value;
var center_sensor_value;
var right_sensor_value;
b.pinMode(left_motor_pin, b.OUTPUT); //left motor pin
b.pinMode(right_motor_pin, b.OUTPUT);//right motor pin
while(1)
{
//read analog output from IR sensors
//normalized value ranges from 0..1
left_sensor_value = b.analogRead(left_IR_sensor);
center_sensor_value = b.analogRead(center_IR_sensor);
right_sensor_value = b.analogRead(right_IR_sensor);
//assumes desired threshold at
//1.25 VDC with max value of 1.75 VDC
if((left_sensor_value > 0.714)&&
(center_sensor_value <= 0.714)&&
(right_sensor_value > 0.714))
{ //robot continues straight ahead
b.analogWrite(left_motor_pin, 0.7);
b.analogWrite(right_motor_pin, 0.7);
}
else if
{
:
:
:
}
}
//***********************************************************************
I understand this code and it makes sense. For exercise #13, we had to
actually fill in the rest of the if-else loop which I did below:
if((left_sensor_value > 0.714) && (center_sensor_value <= 0.714) &&
(right_sensor_value > 0.714))
{
//robot continues straight ahead
b.analogWrite(left_motor_pin, 0.7);
b.analogWrite(right_motor_pin, 0.7);
}
else if((left_sensor_value > 0.714) && (center_sensor_value > 0.714) &&
(right_sensor_value <= 0.714))
{
//The right side is clear, but left and front are obstructed.
//So turn right by turning the left wheel but not the right wheel.
b.analogWrite(left_motor_pin, 0.7);
b.analogWrite(right_motor_pin, 0);
}
else
{
//Turn left
//Default action seems to be to turn left even if the other ways
//are also free.
b.analogWrite(left_motor_pin, 0);
b.analogWrite(right_motor_pin, 0.7);
}
Anyways, according to the book, the second operand to the analogWrite()
function is the duty cycle, so that is clear. But* I don't know what the
motor on time is controlled by*. Does anyone see, because it is not obvious
to me at all.
I can't write the function if I don't know what the variable is or how it
is being used. Thanks for reading and for any helpful replies. If you need
more information, I'll be happy to give them.
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