Hi. I am ok with hardware, soldering, etc, but I want to understand something better.
I have a piece of cardboard and made a 4" x 4" grid and put an led into each one, with pins sticking out of the back of the cardboard. I then bent all the cathodes in each row together and soldered them in a line. 4 lines of cathodes with 4 pins sticking out of the end of each row. I want to control each led individually. So, can I solder those 4 cathode lines together into 1 then just plug it into the ground, or do I have to put 1 or more 220 resistors on each line or the one joined line? Thanks in advance for your time and replies.