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Im quite new to arduino in general and i'm sorry for the beginner question.

could someone explain what the 3.3v and 5v on boards do? I know their voltages. but can you run one on the other? whenever i try to search about it i see people saying that most newer modules are running on 3.3v so they convert their 5v arduino to 3.3v. something about if you run one on the other it could break it.


the arduino I bought looks like it has both! is that even possible?
I also purchased this LED matrix as I wanted to make a wifi enabled scrolling text display. the matrix says it requires 5v. since this arduino says vin is 5-12v the two should connect and work properly, right?

  • The first link is to Amazon and shows a dev board with ESP-12F and USB connector. the other link is a dot matrix with max7129. – Juraj Oct 16 '18 at 19:51
  • the main question here is "will the 3.3 V clock and data signal be read by the 5 V max7129 chip?" – Juraj Oct 17 '18 at 9:22
  • I was not sure if I understand the max7129 datasheet, so I didn't write an answer. CrossRoad gives you an answer. It will not work. You must use logic level conversion. – Juraj Oct 17 '18 at 17:20
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The difference for different voltage boards lies in the parts, that are soldered on it. Often microcontrollers support more than one supply voltage, but impose different performance limits on the system. Take for example the Arduino Uno: It uses the Atmega328p, which can run both on 3.3V and 5V. But on the UNO there is a 16MHz quartz, which generates the controllers clock signal. The Atmega328p cannot run 16MHz with only 3.3 volts. To run a board on a voltage, for which it wasn't directly build, mostly requires you to resolder it with the correct parts.


whenever i try to search about it i see people saying that most newer modules are running on 3.3v so they convert their 5v arduino to 3.3v

There are special chips, called voltage regulators/converters. They come with various working principles, but basically they are converting one voltage to another. The Arduino Uno has one connected to Vin, so that you can apply between 7V and 12V to Vin and the Arduino itself will only see the 5V it get's from the regulator. Some modules also have a voltage regulator, but not all. Be careful not to provide more than the specified voltage to any board or you may destroy it.


the arduino I bought looks like it has both! is that even possible?

First, as Juraj wrote, this is not an Arduino. It is an ESP8266, a totally different chip and board. But you can also program it through the Arduino IDE, without it being an Arduino. Second: When they write, that you can provide it with either 3.3V or 5V, they mean, that you can provide 5V through the USB jack and a voltage regulator will convert it to 3.3V for the ESP, which runs completely on 3.3V. You should not connect 5V to any other pin.


since this arduino says vin is 5-12v the two should connect and work properly, right?

As stated above the 12V is only, what you can at maximum provide at Vin. The ESP8266 runs on 3.3V, so you will have to provide 3.3V (or more over the Vin pin). The LED matrix runs at 5V, as you stated. So you need a 5V source and a level shifter for the 2 lines between the ESP8266 and the matrix. If you connect them directly, you would damage the ESP8266. So: No, you cannot use it directly. It is up to you, if you want to use a level shifter or buy another matrix display, which can be controlled by a 3.3V signal.

  • in the last section you assume Uno. OP wants to connect the matrix to esp8266. the matrix has a control chip which communicates over 2 pins clock and data. will the 3.3 V signal be good for max7129? – Juraj Oct 17 '18 at 9:18
  • Ah, I misread the question and didn't know, that he already has an ESP8266. I will edit my answer – chrisl Oct 17 '18 at 17:13
  • the esp8266 will not be destroyed. it can tolerate 5 V communication over digital pin. and I doubt there is any from the max chip to esp. but the 5 V chip will not understand the 3.3 V as HIGH – Juraj Oct 17 '18 at 19:42
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As seen in the OEM data sheet for the MAX7219 https://datasheets.maximintegrated.com/en/ds/MAX7219-MAX7221.pdf the MAX7219 needs a supply voltage of 4 to 5.5V. with a minimum signal voltage for High of 3.5V when Vcc = 5V.

Folks often get counterfeit parts from e-bay or elsewhere, with unknown characteristics.

For best results, I would power the '7219 from 5V, and use a buffer chip powered from 5V, such as 74AC125, http://www.onsemi.com/pub/Collateral/MC74AC125-D.PDF which will take ~ 2.5V with Vcc = 5V to boost the ~3V output from the ESP2855 to 5V levels.

  • who and why down-voted this answer? (it zeroed my upvote) – Juraj Oct 19 '18 at 16:03

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