Datasheet

Light-Sensitive Navigation with Phototransistors • Chapter 6
Robotics with the BOE Shield-Bot • 201
tone(4, 3000, 1000); // Play tone for 1 second
delay(1000); // Delay to finish tone
Serial.begin(9600); // Set data rate to 9600 bps
}
void loop() // Main loop auto-repeats
{
float tLeft = float(rcTime(8)); // Get left light & make float
float tRight = float(rcTime(6)); // Get right light & make float
float ndShade; // Normalized differential shade
ndShade = tRight / (tLeft+tRight) - 0.5; // Calculate & subtract 0.5
for(int i = 0; i<(ndShade * 40) + 20; i++) // Place asterisk in 0 to 40
{
Serial.print(' '); // Pad (ndShade * 40) + 20 spaces
}
Serial.println('*'); // Print asterisk and newline
delay(100); // 0.1 second delay
}
long rcTime(int pin) // rcTime measures decay at pin
{
pinMode(pin, OUTPUT); // Charge capacitor
digitalWrite(pin, HIGH); // ..by setting pin ouput-high
delay(5); // ..for 5 ms
pinMode(pin, INPUT); // Set pin to input
digitalWrite(pin, LOW); // ..with no pullup
long time = micros(); // Mark the time
while(digitalRead(pin)); // Wait for voltage < threshold
time = micros() - time; // Calculate decay time
return time; // Returns decay time
}
How LightSensorDisplay Works
The loop function starts by taking the two rcTime measurements for the left and right light
sensors, and stores them in
tLeft and tRight.
void loop() // Main loop auto-repeats
{
float tLeft = float(rcTime(8)); // Get left light & make float
float tRight = float(rcTime(6)); // Get right light & make float
After declaring ndShade as a floating-point variable, tLeft and tRight are used in an
expression to get that zero-justified normalized differential measurement. The result will be
between –0.5 and +0.5, and gets stored in
ndShade.
float ndShade; // Normalized differential shade