As for Ground or Common, unless we are measuring very tiny voltages at high current, you can use the same ground point to measure all those voltages from.
A voltage is measured from a reference point, and we use a circuit Common which we usually call Ground.
From the numbers you gave, it sounds like your meter's Continuity setting also works as a Diode Check. Most meters are built that way, now.
2.) when I take RED prob, put it on Vcc (positive supply voltage).. and touch BLACK probe the BASE (pin 1) on the transistors.. * (actually I am touching it to the RIGHT side of the resistor, and not directly tot he BASE pin of the transistors)
Each of the leds light up respectively.. (not very bright or anything.. but about the same it did before) (Im sure changing the 1K resistor values and the 3.9k > 3.9Ohm will help on this a bit though...right?) smiley
Do you mean the black and red probes of your voltmeter? What kind of meter do you have? A typical DMM (digital multimeter) has a resistance of 10M ohm (10 million ohms) and shouldn't cause more than a glimmer of light in the LED, just because that minuscule uA (millionths) of current is being amplified about 100 times by the transistor. Is that what you are seeing? If so, that should mean the transistors are working.
So... with the Arduino disconnected from the LED driver, the LEDs are not lit, correct? If you connect your meter from V+ to the base resistor, that LED lights very dimly, correct?
Ah... with a 220 ohm resistor in place of the 1k, I suggest you also put a 10k (or anything up to about 100k, whatever you have on hand) from the Base to the Emitter/ground.
If I'm reading what you are saying correctly, you have the Arduino switching the wrong way round. Pulling down to light up. Complicated by the fact that tiny bits of leakage current in the transistor may be amplified to light up the LEDs.
I missed that before. You were driving low current 20mA RGB LED before, now with the driver transistors acting as inverters, your code must send a "0" to turn them off, and a "1" to turn them on.
Could you post your code? Don't forget to use the Code tags. Click "Preview", then look for the button labeled with a "#".