Datasheet

Chapter 6 • Light-Sensitive Navigation with Phototransistors
182 • Robotics with the BOE Shield-Bot
void setup() // Built-in initialization block
{
Serial.begin(9600); // Set data rate to 9600 bps
}
void loop() // Main loop auto-repeats
{
Serial.print("A3 = "); // Display "A3 = "
Serial.print(volts(A3)); // Display measured A3 volts
Serial.println(" volts"); // Display " volts" & newline
delay(1000); // Delay for 1 second
}
float volts(int adPin) // Measures volts at adPin
{ // Returns floating point voltage
return float(analogRead(adPin)) * 5.0 / 1024.0;
}
Halt Under the Bright Light
The sketch HaltUnderBrightLight will make the BOE Shield-Bot go forward until the
phototransistor detects light that’s bright enough to make the voltage applied to A3 exceed
3.5 V. You can change the 3.5 V value to one that’s halfway between the high and low voltage
values you recorded from the last sketch.
 Calculate the half-way point between the ambient and bright light voltages you
recorded from the last sketch.
 In the HaltUnderBrightLight sketch, substitute your half way point value in place
of 3.5 in the statement
if(volts(A3) > 3.5.
 Run your modified version of HaltUnderBrightLight on the Arduino.
 Hold your flashlight or lamp about a foot off of the floor, and put the BOE Shield-
Bot on the floor a couple feet away but pointed so it will go straight under the
light.
 Move the power switch to position 2 so the BOE Shield-Bot will drive forward.
How close did it get to stopping directly under the light?
 Try making adjustments to the threshold you set in the
if(volts(A3)
>…)
statement to get the BOE Shield-Bot to park right underneath that bright
light.
/*
* Robotics with the BOE Shield - HaltUnderBrightLight
* Display voltage of phototransistor circuit output connected to A3 in
* the serial monitor.
*/