How to use Level Shifters
The Uno, the most popular of the Arduinos uses 5V logic. In most cases this is just fine, but sometimes you need to connect to a peripheral that uses 3.3V logic. While the Uno (and the nano and the mega) have a 3.3V power pin to power these devices, the GPIO pins will output 5V for a logic high.
If you try to use this with a device that is only 3.3V you will most likely damage it. So you have two options. First, use a 3.3V Arduino like the Pro Mini. Second, you can use a level shifter. A level shifter will take the 5V logic high and knock it down to 3.3V through an internal voltage divider.
Some level shifters are bi-directional and can both take 5V down to 3.3V and 3.3V up to 5. In this video we will be using one of these bi-directional level shifters. It uses the voltage divider to go from 5V to 3.3V and a PNP epitaxial silicon transistor to go from 3.3V back to 5V.
Here is a link to the unit we are using:
http://www.ebay.com/itm/141980062455?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT
-~-~~-~~~-~~-~-
Please watch: "Diodes: The basic building block of all digital circuits"
https://www.youtube.com/watch?v=Lyii5I30gw0
-~-~~-~~~-~~-~-