Logic high?

Hello, I have a feeling it's really simple but I attempted to figure this out and can't...

I pretty much have this setup like below, 3 sensors, then to the UNO.

Can someone please tell me where 'logic high' is on my UNO? and what do they mean by AD (AN goes to AD).

Much appreciated...

I know i need some serious basics. i plan to pick up a class or book before i get deep in a project i can't handle.

Logic High means on the output pin:

pinMode (pinX, OUTPUT);
digitalWrite (pinX, HIGH);
delay(250); // or more
// now high impedance
pinMode (pinX, INPUT);

CrossRoads: Logic High means on the output pin:

I think you got the timers mixed up. The 250 mS was after power-up. The pulse was 20 uS.

delay(250);  // or more to make sure power is up on the sensors.
pinMode (pinX, OUTPUT);
digitalWrite (pinX, HIGH);
delayMicroseconds(20);  // Keep the line high for 20 microseconds
pinMode (pinX, INPUT);  // now high impedance
digitalWrite(pinX, LOW);  // Make sure the internal pull-up is off
[/quote]

AD input presumably means "analog->digital input", ie. an analog input.

THANKS A LOT GENTLEMEN!!!