It is the voltage a board uses to represent a digital high signal. Boards and sensors work at one or the other, and connecting a 5 V output to an input rated only for 3.3 V can damage it; a level shifter or a part rated for both is used to join the two.
Logic level mismatches are among the most common reasons a first electronics project stops working or damages a part.
What a logic level is
A digital pin signals high or low by voltage. A 5 V board treats a signal near 5 V as high; a 3.3 V board treats a signal near 3.3 V as high. Many classic boards run at 5 V; many newer boards, including most with built-in wireless, run at 3.3 V.
Where the risk is
A sensor powered at 5 V can output 5 V signals. Connected to a 3.3 V input that is not rated for it, that voltage can damage the input. The reverse direction usually does not damage anything but may not be read reliably.
How the two are joined
A level shifter converts signals between the two voltages. Some sensor modules include their own regulator and level shifting, which their listing or documentation states. For slow, one-way signals, a simple voltage divider is sometimes used, following a published circuit.
Where to look
The board maker’s documentation states the operating voltage and whether any pins tolerate more. The sensor’s datasheet or module description states its supply range and output levels. Checking both before wiring takes a minute and saves a board.
Questions makers ask before buying
How do I know whether a pin is 5 V tolerant?
From the board’s or chip’s documentation. Some 3.3 V boards list individual pins as 5 V tolerant; many do not, and without that statement the pin should be treated as 3.3 V only.
Can a 3.3 V output drive a 5 V input?
Sometimes, if the 5 V part recognises 3.3 V as high, which its datasheet states. It is not guaranteed, and a level shifter removes the doubt.
Last reviewed 15 September 2026