Because the Arduino (and Basic Stamp) are 5V devices, and most modern sensors, displays, flash cards and modes are 3.3V-only, many makers find that they need to perform level shifting/conversion to protect the 3.3V device from 5V. Likewise, level shifting may be needed when trying to use the Raspberry Pi (3.3V) with 5V sensors and devices.

Although one can use resistors to make a divider, for high speed transfers, the resistors can add a lot of slew and cause havoc that is tough to debug. For that reason, we like using 4050/74LVX245 series and similar logic to perform proper level shifting. Only problem is that they are only good in one direction which can be a problem for some specialty bi-diectional interfaces and also makes wiring a little hairy.

That's where this lovely chip, the TXB0108 bi-directional level converter comes in! This chip performs bidirectional level shifting from pretty much any voltage to any other voltage and will auto-detect the direction. Only thing that doesn't work well with this chip is i2c (because it uses strong pullups which confuses the auto-direction sensor). If you need to use pullups, you can but they should be at least 50K ohm - the ones internal to AVRs/Arduino are about 100K ohm so those are OK! Its a little more luxurious than a 74LVX245 but if you just don't want to worry about directional pins then this is a life saver!

This breakout saves you from having to solder the very fine pitch packages that this chip comes with. Adafruit have also added 0.1uF caps onto both sides and a 10K pull-up resistor on the output enable pin so you can use it right out of the box!

Features

• 1.2 V to 3.6 V on A Port and 1.65 to 5.5 V on B Port (VCCA ≤ VCCB)
• VCC Isolation Feature – If Either VCC Input Is at GND, All Outputs Are in the High-Impedance State
• OE Input Circuit Referenced to VCCA
• Low Power Consumption, 4-uA Max ICC
• Ioff Supports Partial-Power-Down Mode Operation

Useful Links

TXB0108 Datasheet

An app note for the TXB0108 detailing how it works!