Note: here we cover digital signals, not analog signals That is (mostly) because of logic levels! Your board would likely still power on in this case, as the Atmega328p can run on a pretty large range of voltages, but for the Arduino Nano application specifically, you are asking your trouble. With a 5V input, the output will be about 3.3V. If you have a look at page 6 of the LM1117 datasheet, you'll find that the minimum voltage required for a 5V output is 7V. Notice that the Arduino Nano VIN is not directly connected to the Atmega328P chip, rather it is connected to the input of an LM1117 5V regulator IC, which can be seen on the bottom of the Arduino Nano board. That can be explained here: Arduino Nano VIN and 5V regulator circuit You might be wondering why the minimum input voltage for the VIN pin (7V) on an Arduino nano would be so much higher than the operating voltage (5V) on the device. This means that in order to function 'as intended' it must be powered with a stable 5V DC. For the Atmega328P chip used in the Arduino Nano application, that would be 5v. Operating voltage refers to the actual voltage (or range) a component expects to operate at. In other cases, like the Arduino 'VIN' pin, it might be a large range, since there is a circuit that allows input from 7-12V since it will be converted (stepped down) to lower voltages for the device. Sometimes this might be pegged to a particular number if there is no way to regulate the voltage. Power and Logic Voltage Levels Input voltage and operating voltage (power)ДЄ device or component might have a rated input voltage, which is the range of voltages the device will be able to successfully take and use to power all of its components. With this guide I'll try to help describe for beginners why operating voltage and logic levels matter, and how you can decide which to incorporate in your project. When I first started working with these, I didn't really understand why it mattered and kind of just decided, 'I'll just use all 5V and pretend 3.3V doesn't exist.' I very soon found out that I couldn't just ignore 3.3V. Usually, you'll see 5 volts and 3.3 volts (also marked 3V3 in schematics) indicated somewhere on these boards. If you work with electronics, be it microcontrollers like an Arduino Nano or SBCs (single board computer) like a Raspberry Pi, you've surely noticed that there is more than one voltage level marked on these boards.

Arduino logic levels