2N2222 multiplexing oddity

Using Arduino LEDs and Multiplexing
1

Hello! I am working on an LED cube for fun and practicing the use of transistors in a nice way. I've experimented with transistors a bit before, but I'm running into something that is making me a bit confused.

I am currently using 4 transistors (all 2N2222) to control the ground (X) (which, for the cube, is linked per 4x4 segment), and 4 transistors to control the Z axis of the cube. Due to this layout, 16 others are operating the individual anodes (which are per row (X) per layer (Z)), where the origional idea was to use the 16 in groups of 4, where the pins from the Arduino (Pins 8-11) control one of each in the groups of 4 and the 4 previously mentioned transistors control which group get power (Pins 4-7). In theory, this seemed okay until I started to notice the cube would illuminate everything as if all the 'power' transistors are giving power to all groups. The control on the group pins however seem to be working okay, as is the ground.

I looked up in Google about the transistor and found this. The issue is their solution revolves around controling the cathode, which I already am and with correct operation. My goal is to now control the anodes but if the transistors are just going to act like 'diodes' then doesn't that defeat the purpose of being a transistor in the first place?

My question is how do I go about solving this? The logic of the program is okay, but this circuitry issue is giving me a headache.

-Flame

4x4x4 issue.png
4x4x4 issue.png511×607 3.5 KB

2

You have no base resistors on the transistors, while you are using the transistors in common collector mode this is not a problem, with your cascaded circuit it is because you are not connecting the collector to anything when the tool transistor is off.
Also those top transistors are going to have their base voltage lower than the emitter voltage which could easly damage them.
In short the circuit is all wrong.

3

I considered using resisters but the only way I could achieve desired results was when I had a 10k resistor on the pin before the transistor.

I had a feeling it was the circuit because I could get the bug if I applied the voltages myself in place of the pins. My only issue is I am not fully sure why, since I would assume the transistor would only act like an electronic switch. I'm not an electrical major, so I am only applying what knowledge I know (most of which is basic rules like don't try pumping 5v through 3v LEDs unless you have a resistor good enough to drop the voltage down safely, which is 1k ohm).

Considering the structure in place, what should I look into to better understand how to resolve the issue and/or what chances to the circuit itself should I place in to fix it?

4

Yes you need to find out how transistors work, try this:-
http://www.kpsec.freeuk.com/trancirc.htm