Problems reading second pin

Development Tools IDE 1.x
1

I've got proximity sensors connected to pins 10 and 11. I'm using digitalWrite and digitalRead as below but pin 10 always reads zero. It doesn't matter whether I run the program with pin 10 or 11 first. Both pins operate as expected when only one pin is manipulated (set both _pin to 10 or 11). I see many posts in the forum using multiple pins but nothing that clues me in. Here's the code.

void setup()
{
Serial.begin(9600);
}
void loop()
{
long duration;
int _pin;

_pin = 11;

pinMode(_pin, OUTPUT);
digitalWrite(_pin, LOW);
delayMicroseconds(2);
digitalWrite(_pin, HIGH);
delayMicroseconds(5);
digitalWrite(_pin,LOW);
pinMode(_pin,INPUT);
duration = pulseIn(_pin,HIGH);
duration = duration/74/2;

Serial.print("Pin ");
Serial.print (_pin);
Serial.print (": The distance to obstacles in front is: ");
Serial.print(duration);
Serial.println(" inch ");

delay(500);

_pin = 10;

pinMode(_pin, OUTPUT);
digitalWrite(_pin, LOW);
delayMicroseconds(2);
digitalWrite(_pin, HIGH);
delayMicroseconds(5);
digitalWrite(_pin,LOW);
pinMode(_pin,INPUT);
duration = pulseIn(_pin,HIGH);
duration = duration/74/2;

Serial.print("Pin ");
Serial.print (_pin);
Serial.print (": The distance to obstacles in front is: ");
Serial.print(duration);
Serial.println(" inch ");

delay(500);
}

2

Providing more information. We swapped out the Uno with a Mega 2650. I've tried other pins combinations (currently at 30 and 40). The proximity senors are 3 pin Ultrasonic Range Sensors from Radioshack.

3

The problem is timing. This code change fix it.

pinMode(ProxPin1, OUTPUT);
digitalWrite(ProxPin1, LOW);
delay(2);
digitalWrite(ProxPin1, HIGH);
delay(10);
digitalWrite(ProxPin1,LOW);
pinMode(ProxPin1,INPUT);
duration1 = pulseIn(ProxPin1,HIGH);