Running MAX7219 at 3.3v with ESP8266?

Question

I just got a 4 chained 8x8 LED max7219 displays with a 5 pinout, these are very popular https://www.amazon.com/Wangdd22-MAX7219-Arduino-Microcontroller-Display/dp/B01EJ1AFW8/ref=sr_1_5?s=books&ie=UTF8&qid=1520880134&sr=8-5&keywords=MAX7219

I've seen several ESP8266 tutorial projects using these that are using onboard 3.3v output, everything plugged directly into the LED display. Here is one: https://www.youtube.com/watch?v=mn9L85bhyjI

However the max7219 spec sheet says 5volts, and I see nothing about it supporting 3.3v.

So far, I've gotten them to work fine with the +5v from the Arduino directly connected. They also work with the +5v on the raspPI, but it has locked up a few times (I read the raspPi has a hard time running more than 2 displays without external power to the display).

My question is:

How/Why does it work on 3.3v? Is it safe to operate it this way? If not, what can happen? Is there a better (e.g. "more proper") way to wire it to a ESP8266?

Thanks!

Answer 1

Since you are only writing TO the MAX7129 and not reading from it, what matters is that it sees your inputs correctly. On the datasheet the minimum input voltage for a high is spec'd at 3.5V. In reality it is probably less than that, and typically in the 1.5V range, but this is not guaranteed. However, for non-critical applications, it should work.

You can test what the actual threshold is. Put a potentiometer from +5V to GND with the wiper on the DIN input instead of a connection from the ESP8266 and write to the display. Vary the potentiometer setting to find the voltage that the MAX7129 clocks in as 1s instead of 0s. As long as the threshold is sufficiently below 3.3V (~2.3V or less is good, ~3.0V or higher is marginal), it should work fine.

As for the PI lockups, it definitely has problems if you overload the +5V, so make sure the PI supply has sufficient current if you are powering the modules off of it.

Answer 2

If your question is related (not only to 3.3V interface, but also) to supply voltage of 3.3V for this part, than I was using MAX7221 (similar part with same datasheet and identical electrical characteristics) in combination with MSP430, both on 3.3V. Even minimum supplay voltage from datsheet is 4.0V I didn't have any problem with running it on 3.3V.