# max7219 more current

how to put 4 led *2V(20mA) for single segment is this a good choise 2*2 parallel on 16-20 mA each ? I am afraid becouse the sistem will work on maximum level ~40mA for segment

REGARDS FROM BULGARIA

You need to put a resistor in series with each segment of the display.

If you have 2V drop across the LED then for a 5V supply you need to drop 3V across the resistor. (3 = 5 - 2) Using ohms law E=I*R you have a resistor you want to have 3 volts across with 20mA flowing through it.

This gives you a value of:- R= 3/0.02 = 150 Ohms for each resistor.

If you're trying to wire 4 LEDs in series per segment, you'll need 8V to even light the LEDs, which you wont be able to get from the 7219. I had the same problem with some 7 segment displays:

http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1212882269

Still not having much luck. I'm currently looking into high voltage sink drivers from Allegro, with common anode displays.

maxim have example how to sink more current with MOSFET and 7219