Adafruit VCNL4010 Proximity/Light sensor
The VCNL4010 sensor is a nice way to add a small-distance proximity sensor to your microcontroller project. The VCNL4010 is designed for much short distances, no more than 200mm (about 7.5") and under, experimentation found it worked best at distances of about 10-150mm. It would be good for say detecting when a hand moved nearby, or before a robot smacks into a wall. The sensor also has an ambient light sensor built in.
This sensor is easy to use with any microcontroller that has i2c capability. It is 5 volt compliant so you can use it with 3.3V or 5V logic with no risk of damage. There is an onboard 3.3V ultra low dropout regulator so you can power it with 3.3 to 5.0V. However, if you can give it 5.0V that is ideal since the VIN voltage powers the IR LED and the higher the voltage you can give it, the more powerful it is.
New! Since Sept 23, 2015 we are now shipping this breakout with the updated VCNL4010 - the library has changed and the chip is slightly different in that it now supports interrupts. Adafruit have also made the board a little more compact. However, the overall proximity functionality is identical.
Adafruit provide a tutorial guide with all the details on how to use the VCNL4010 in both Arduinoand CircuitPython on their website. Including have wiring diagrams, code, examples, datasheets and more!