I think you mean the digital pin to the base? (Edit: I see you fixed that already. It's good practice when you edit, to show what you changed... else others will think I'm imagining things....)The npn requires the load on the high side, so from the top down, you have:Power +veLoadCollectorEmitterGround (same as power -ve)Then on the "side" so to speak you have:Controller digital pin to base (through a resistor)Controller ground to same ground as the transistor, which is the same as the Emitter.But I don't really understand your question.....The grounds need to be common so that all voltage measurements have the same reference. If the controller ground isn't the same as the equipment ground, then the transistor has no 0 for the controller io signal, and it's a bit like imagining one hand clapping.Edit: I guess it's easiest to say that the Arduino ground, the power supply -ve, and the emitter are the same point.
The current will flow from the base to the emitter , base being the "positive" side of the circuit and the emitter being the "ground".
If I can put it in another way, say u have 2 1.5v batteries, or two power supplies. You take one battery/power supply and connect a wire from the positive terminal to the load, then you take the second battery/power supply and connects the ground wire to the negative side of the load. You see the two batteries/power suppliesAre separate from one another but the load still see's a positive and a negative? Why can't this work?
Ok thanx, that kinda makes. Just a another question, why does the power circuit the arduino is driving not effect the arduino's ground? Like what prevents ,say we are switching a 100v 20A power circuit, the high current from not going into our arduino's ground?does the current say "no wait that's not my vcc's ground hence I will not go there"
The way I understand ground is a place for electrons to flow to
QuoteThe way I understand ground is a place for electrons to flow toThat is where you are wrong. A ground is a bit of an abstract concept and any point in a circuit can be considered a ground.But it has to be a circuit, see:-http://www.thebox.myzen.co.uk/Tutorial/Power_Supplies.html
A ground is a bit of an abstract concept and any point in a circuit can be considered a ground.