When interfacing various devices to a microcontroller, some kind of voltage conversion is often needed. The most common voltage levels of development boards and modules are 3.3 V and 5 V, yet it is not out of the ordinary to find devices using 2.5 V or even 1.8 V I/O levels. This post will explore some of the available methods of converting I/O voltage levels to ensure compatibility between electronic modules and ICs. When I say compatibility I mean the devices connected together through a level shifter should work as expected and not cause damage to each other.
I began searching information about level shifting after a failed attempt to interface an ESP8266 board (3.3 V I/O) to an array of 74HC595-74HC165 shift registers which were required to be powered at 5 V (therefore they expect 5 V I/O). Without documenting too much, I considered 74HC would recognize high 3.3 V output from microcontroller. But that was not the case as I would soon discover. The next step was to add a MOSFET bidirectional level shifter (the ones which are commonly used for I2C), however strange behavior occurred.
