Multiplexing array questions.

Other Hardware LEDs and Multiplexing
1

I am trying to build an 8x8 array of LEDs for playing/testing. One reference uses a transistor to limit the power needs and another does not even bother in their schematic. So here are my questions....

  1. Does it make any difference to the Arduino for common anode or common cathode?
  2. What transistors would be recommended? I have BC307b (pnp) and getting 2n2222 (npn) would these work?
  3. How many rows/column can be used before a noticeable change in brightness or flickering is seen?
  4. Are there any Arduino pins that should be used or avoided for this multiplexing application?
  5. Can rows or columns be "faded" by turning on/off rapidly?

Any advise or thoughts would be greatly appreciated as I'm just starting tp play with these things....

Dan

2

  1. not really if your writing your own code, if not it may make a difference, its really the difference of flipping on power or connecting stuff to ground.

  2. I would use the 2n2222 just cause (when the base is on so is the transistor, pnp when the base is off the transistor is on), and yea it will work fine

  3. good question, I have a 32x32 matrix that requires a bit of magic to get going flicker free, but its not THAT magical

  4. any of the digital pins would be fine, avoid 0 and 1 as they connect to the serial port of the chip and are used for programming

  5. yes, though its not the easiest thing in the universe for someone starting off

3

One reference uses a transistor to limit the power needs

No a transistor will switch current it will not limit it for that you need resistors.

and another does not even bother in their schematic.

There are a lot of crap circuits about that damage your arduino, that sounds like one of them.

For an idea of what you need to do when driving a matrix,
See this:-
http://www.thebox.myzen.co.uk/Workshop/LED_Matrix.html