I have a transistor which will be triggered by an arduino digital pin. When the transistor switch is closed, ~5 A is going to flow from the collector to the emitter. However, I was under the impression that both the base and the emitter need to be grounded at the same place. I'm worried about that kind of current going into the Arduino's ground, because I've heard it can't handle that much current. Is there a better way of doing this? Any advice is much appreciated.
Edit: I'm using a TIP3055 transistor and switching 12 VDC.
Best Answer
You have stumbled upon a very, very important issue. Take a look at two circuits with slightly different topologies:
The first circuit, as you can see, has the return lines branching out from a node that is close to a stable ground. In the second circuit, the currents returning from power circuits flow through the microcontroller's return line. The trace inductance and resistance will have a potentially significant voltage drop. A voltage across a "gnd" trace will cause your Arduino's power supply to be corrupted with unncecessary noise. Furthermore, the connectors that your arduino uses are rated up to 1A. The pcb traces pcb are even more prone to damage.
Connect your circuitry according to the upper image and your high current signals won't fry any traces on your Arduino.