Pi => Nano => MAX7219

[morgon123]

Hi,

as a total arduino and electronics-noob I am just looking for some feedback on whether or not what I am planning to do would be feasible and easy enough for me to tackle...

What I want is a 8x8 MAX7219 led matrix to occasionally display status information from my Orange Pi Zero 3.

Originally I wanted the led-matrix to be directly controlled by the pi but there seems to be a problem with device tree overlays and the spi interface is currently not working properly on the pi, however the led-matrix works absolutely fine with an arduino nano clone that I have, so my new idea is this:

I attach the led-matrix to the nano and connect the nano and the pi via usb so that they can communicate serially. Whenever the pi wants to use the led-matrix it sends a command to the nano via the serial port and the nano then controls the leds accordingly. Such a sketch should not be too hard to write (I think). Are there any libraries one could use for implementing the serial communication apart from the Serial-class I already have seen?

However I only need this functionality only rarely and so I would like to have a way to completely turn off the led-matrix.

Unfortunately it seems there is no way to control the 5v pin via software so from what I have gathered you would need to use a mosfet and this is something I know nothing about...

Would it be possible to get the power from the 5v pin (that get's it's power from usb) but have a mosfet in-beween so that the nano would be able to completely turn the led-matrix on and off or would you say such a complexity is not needed as the power consumption would be minimal when all leds are turned off anyway?

So is this a good idea that can be tackled by someone with a background in programming but no know-how in arduino or electronics (in particular I cannot solder)?

Many thanks for all feedback.

[DaveX]

@morgon123

Unfortunately it seems there is no way to control the 5v pin via software so from what I have gathered you would need to use a mosfet and this is something I know nothing about...

A high-side power switch module like this could work for controlling a 5V pin:

Pololu - Mini Pushbutton Power Switch with Reverse Voltage Protection, SV

Look into this:

Serial Input Basics - updated

Updated Version Please note that this is a revised version of the advice in this earlier Thread which has become very long. As far as possible I have kept the code examples identical or simplifed them slightly. It should not be necessary to refer to the older Thread, but feel free to do so. Contents The following sections are in this Tutorial Introduction Serial data is slow by Arduino standards Example 1 - Receiving single characters Why code is organized into functions Exampl…

[flashko]

@morgon123

Whenever the pi wants to use the led-matrix it sends a command to the nano via the serial port and the nano then controls the leds accordingly. Such a sketch should not be too hard to write (I think).

This is generally the more complicated option, especially for beginners. Even for advanced users, I would not recommend it because it hides more problems and difficulties compared to the benefits. I have always tried to use only one microcontroller for a given task. It is not mandatory to use a hardware SPI with this MAX7219 chip. You can use any digital output pin and it will work as it just the data transfer rate will be slower but I don't think that will be a problem.

@morgon123

However I only need this functionality only rarely and so I would like to have a way to completely turn off the led-matrix.

To save energy, if I'm not mistaken, the MAX7219 has a command to turn off all output segments, so it will consume very little current. It may be sufficient for your purposes.