First Project - Needing guidance for schematic so far

Hi, this is the first time I will be working with an Arduino and my first electronic project as well. I have a small background regarding soldering and electronics work but nothing big. I am a programmer fluent in a couple of languages and so far the Arduino way of programming is quite simple.

My project is to make a 2 x 16 LED matrix and so far I have completed my schematic for it. Before jumping right into the actual hooking up process, I wanted to have your input on it to make sure everything looked right. I'm the kind of person who likes good preparation. :slight_smile:

Here is the schematic:

The first question you may ask is why the LEDs are hooked up in such a way. My goal is to have the second 2 x 8 matrix be a direct mirror of the first matrix. ( hope you understand what I mean :blush: )

Also, I thought the MAX7221/MAX7219 required a resistor? This is all quite new to me so I am open to any pointers!

Thanks for your time!

yes the MAX7221 needs a resistor to set the amount of current each LED will receive, look at

page one for a typical example, and page 10 and 11 for details

Thank you for the input! Much appreciated. Now that you point it out, it all makes sense. Following your advice, would you reckon a 10 kilo Ohms resistor would be enough for this setup?

what color are your LED's?

different colors have different forward voltages

and no, most standard issues LED's are going to like 40ma for more than a very fast pulse (which you may have, but I would not push it for a learning project)

Current selection is discussed in the datasheet, along with power dissipation. Suggest doing some reading there.
Your schematic is not correct. Arrange your LEDs in columns of 8 - each column will have common cathodes connected to a digit pin. All LEDs will have Anode rows in parallel to the Segment pins.
If you have 2 LEDs in parallel in each column, make sure the LEDs are purchased in the same lot of parts, and don't program the current as high - power considerations will apply.

If you haven't purchased parts, suggest you start with MAX7219 from taydaelectronics.com, $1.25 each. MAX7221's seem to be a lot more.
Both can be identically addressed with SPI.transfer( ) commands.