Maxim 7219 - how do you adjust the current going into each segment of a seven segment display
The MAX7219 is a constant current source.

It uses the resistor connected between \$V_{cc}\$ and \$I_{set}\$ to set the current delivered to each LED.

It also multiplexes the 8 digits, so only 1 digit is "alive" at any one time.

Thus, the maximum current draw by a display, no matter how many digits you have, will be \$I_s \times 8\$ (8 is 7 segments plus the decimal point, \$I_s\$ is the current of a single segment).

The datasheet gives a very handy table with typical values for the resistor depending on the forward current and the voltage of a single segment.  This all depends on the displays you are using - check their data sheet for this information.



So for a display that has a 2.5V voltage and 20mA per segment, you would use a 28KΩ resistor.

I have come across a page on the Arduino site which gives some good information about the RSET resistor.