Look for typical power supply voltage (VCC) and input voltage levels which are described as VIL (low input voltage) and VIH (high input voltage). The useful information can be found in the electrical specifications section. Only the datasheet of the integrated circuits you are trying to interface can give a proper answer. Is level shifting really needed for my application? This logic "1" level, also known as logic high, is closer to the supply voltage of a device, while the logic "0" (low) level is closer to ground. We are assuming the need to interface two devices which share the same ground, but output different digital voltage levels.
In this post I will refer to level shifting as the process of converting the logic "1" voltage of a digital I/O to different voltage levels. The next step was to add a MOSFET bidirectional level shifter (the ones which are commonly used for I2C), however strange behavior occurred. But that was not the case as I would soon discover. Without documenting too much, I considered 74HC would recognize high 3.3 V output from microcontroller. 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). 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. This post will explore some of the available methods of converting I/O voltage levels to ensure compatibility between electronic modules and ICs. 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.
When interfacing various devices to a microcontroller, some kind of voltage conversion is often needed.
Common voltage levels of digital circuits and basic level shifting required to drive lower voltage devices
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