How do i determine the resistor value when using different size seven segment displays with a MAX7219?
For example 4, 2-Diigit displays. Or 2 3-Digit and, 1 1-Digit?
Is that possible? I have specs for 7 Segment displays. They refer to Forward Voltage Vf/seg and Luminous Iv/seg
Here is example of my 2 Digit Display.
5V - 2.3V / .02mA = 135ohms
Is this correct? Or do i multiply by for each segment of the digit?
Thanks
You could use a 100k potentiometer. With that table, looks like you'd want a minimum setting as well, so put a 10k resistor in series with the 100k pot.
If you have dissimilar LEDs wired to the same 7219(e.g. 4 red 7-segment and 2 green 7-segment), you'll have to come up with a compromise, because there's only one R-set.
I am using 3622AG and 3631AG
Here is the datasheet i was referencing. Did not mention kilo. Is that datasheet for the MAX7219?
Seven Segment LED 3622AG.pdf (156.4 KB)
Yes
Since your display has a typical segment forward voltage of 2.3V, you could use the 2.5V column to pick your Rset.
Ah got it! And the Reverse Current for the LED says iR 30 Max. Does that mean i look at the 30 row in that chart?
You would use the forward current specification which is 25mA max.
now i understand! Thanks for making it easy to understand! Really appreciate it!
You’re welcome. The MAX7219 has lots of options that you can set in software. If you’re curious, read the data sheet and study the software library documentation.
Thanks for the suggestion
So what resistor value have you chosen ?
And mark the topic as solved so that anyone finding it in a search engine will know that the question was answered.
If i'm correct, should use a 13k ohm resistor. For that particular LED.
That would put me between 20mA and 30mA
For 20mA segment current you would use an Rset between 25.9K and 28.0K. Do you see how I got that?
Dam, went the wrong way. Yes
So just to make sure you’ve got it, what value Rset would you use for 10mA segment current?
if my forward voltage is the same at 2.3v then i would use 59.3 - 63.7 k
Bingo! 
Yes, was going to use between 20 and 30 mA
