I tested the circuit below with an Arduino UNO, a MAX7219 and BC338. The sketch in Arduino is a chaser, so the leds should turn on in sequence. It consist of 7 segment (A-G) and two Digit (0-1).
The problem is that when one segment is turned on (and only that led sould be), also the same segment on the other digit is turned on. The problem si showed in the image below.
I tried with pull-up resistor and other tests, but I don't know what's the problem. Thank you for your help.
Best Answer
Brhans is right you can't put NPN transistors there you either need a pullup resistor or PNP there but i fail to see the point since inside max u already have a NPN transistor driving that line. I think you will have better luck if you explain what you are trying to accomplish, im guessing some weird dimming or something similar witch wont work anyway. Have in mind that 7219 uses multiplexing as a means to drive more than 8 leds.