I’ve done some searching about this, and there’s certainly lots of confusion & questions about this, but none that cleared up my question.
Here’s what I’m doing:
I wiring my own 64 LED matrices that I currently plan to drive with a number of MAX7219s. I have used the MAX7219 a number of times, so the code and wiring is something I have a handle on. What I don’t quite understand is how to arrive at the correct RSET resistor value when I’m wiring the matrix. For clarity, the MAX7219 uses a single resistor between the ISET pin and the 5V supply for all the LEDs controlled by the MAX7219.
The maximum current of the MAX7219 is rated for is 500mA:
I intend on using an LED such as this:
These LEDs individually have a 20mA forward current, and a 3.8V voltage. Do I multiply the amperage by 64 to get the value to apply to resistor table for the MAX7219? 64 x 20mA puts the value way outside the table in the datasheet, which is in a range of 10mA to 40mA. That single RSET resistor appears to set the peak for all LEDs, but in the MAX7219 datasheet RSET table, it refers to “segment current” and not overall device current.
What I’m really trying to figure out is the brightest LEDs I can use in a 64 led matrix with the 500mA ceiling of the MAX7219. In the use of the matrix, I will frequently be lighting all of the LEDs at the same time. I’m wiring the LED matrix myself because I need control of 64 x numberOfBoards LEDs, and they will not be in the usual 8x8 grid.
The MAX7219 RSET table is attached.