What I came up with was an infrared distance/proximity sensor that sensed an object up to about 10-12 inches away all for about $3.
It is fully compatible with Arduino and other microcontrollers such as PIC, PICAXE, and Parallax Propeller (although the code would have to be different than the Arduino code I will be showing you).
Step 1: How does it work?
1. An IR (infrared) LED emits a pulse of light at the rate of 38KHz. The pulsing rate of the LED is controlled by an Arduino's PWM output.
2. An IR Receiver module is connected to a digital pin on the same Arduino. This module can detect a IR light signal that is pulsing at 38KHz, which is the speed that led Infrared LED next to it is flashing.
3. If there is an object in front of the IR LED and the receiver, the object reflects some of the light back onto the receiver. The receiver detects this light and sends information back to the Arduino.
4. If the receiver detects an object, it sends LOW to the Arduino's digital input. If it does not detect anything, it sends HIGH.
5. The Arduino then processes this and uses it to control a device of your choosing. It can be anything from an LED to a servo motor to a solenoid.
Step 2: What you will need
1x 5mm IR (infrared) LED (can be narrow or wide angle)
1x IR receiver
1x Regular straw, any color (not those super fat ones you get from some fast food restaurants)
1x 3-4 inch piece of electrical tape
1x Arduino or other microcontroller (to control the LED and pick up signals)