74AHCT125 - Quad Level-Shifter (3V to 5V) - A -US$1.50
https://www.adafruit.com/product/1787

DESCRIPTION

Level shifting chips let you connect 3V and 5V devices together safely. 

This chip is similar to others in the shop (such as the 74LVC125) except ***this one is particularly good at converting 3V logic up to 5V***. 

(1) ***Just power the 74AHCT125 with 5V, it will detect 3V logic properly***. 

(2) ***You can also use it to connect 5V logic out to 3V logic in***, that's ***when you want to power the 74AHCT125 with 3V, it can safely read 5V logic on the input pins***.