Hi guys I am using a 2N2222 transistor one Arduino output as Emitter and another as base. So what is the input current?
Be careful.
Just connect the base to the Arduino. Do NOT connect the emitter or collector of a transistor to an Arduino digital output pin.
The emitter usually goes directly to ground. The collector has some load attached to it.
There is another very recent thread in the "general electronics" forum right now concerning your question (2N2222).
However, you have to find out for yourself whom you will believe.
Also be sure and put a resistor between the Arduino and the base of the transistor, as it can damage the Arduino (and possibly the transistor) if you don't. The value of the resistor depends on the current you expect the load to draw, but for something using 100 - 500 mA you might use one in the range of 470 ohms to 4.7k ohm.
So the question is why are you doing this? You do know transistors cannot tolerate reverse bias on the
emitter-base junction of more than a few volts, so you've set yourself up to risk popping the device.