Hello, I am new here and trying to refresh my electronics after 15+ years of doing software only (most of it relatively low-level - drivers, reverse engineering, lots of disassembly and program analysis for x86/arm/mips/microcontroller code etc. but unfortunately, haven't dipped my hands into hardware things since university)
So, I was looking at this diagram: (Arduino Tutorial pages)
and wondering what's the exact reason for having the negative of the 9V battery (feeding the motor) connected to the GND.
Could we just have it not connected? What would be the consequences? Could it be that D9's current wouldn't have a way to "get out", and the battery or motor would overheat? Thanks. (And I apologize for what is certainly a very silly question, as well as my phrasing / poor terminology: I think I forgot most things except for V=RI and have to re-learn everything from the grounds up I realize)
Ground is needed so the current can flow and to complete the circuit. Touch the postive of any battery, nothing happen, because the circuit is not complete... in order for the circuit to be complete you have to connect the other end into the circuit for the "return".
In your example... D9 applies voltage to the gate of N channel mosfet which opens the gate to complete the circuit turn on the motor using full battery power. The mosfet needs the difference in potential between gate and source, the only way to insure this will work is by connecting the ground. Otherwise it's "floating" which is never good.
Thanks folks. "the current can flow and to complete the circuit." I understand that, but I'm wondering why the current would not able to flow to the negative of the battery itself? Why does it need to be connected to Ground?
(After all, if I simply connect a 9V battery to a motor, the motor rotates.)
Maybe it's easier to see it as two circuits. In the first circuit, the signal of the Arduino goes through gate and source back to the Arduino gnd. In the second circuit, the battery plus goes through the motor, the drain and the source of the mosfet to the negative of the battery.
The source of the mosfet is common so gnd of Arduino and negative of battery are connected.
wolframone: "The mosfet needs the difference in potential between gate and source, the only way to insure this will work is by connecting the ground. "
Intuitively, I understand that this is the problem, the charges needs to flow. But then, isn't the potential difference between the D9 (gate) and battery-minus (source) enough? I will try and experiment that as soon as I can get my hands on a multimeter and the rest of the components.
nicksim:
Intuitively, I understand that this is the problem, the charges needs to flow. But then, isn't the potential difference between the D9 (gate) and battery-minus (source) enough?
No. D9 will be at 5V but that's relative to the Arduino GND as reference. If the battery -ve is not connected to GND then the MOSFET gate does not have access to that reference point. So from its perspective D9 has no clear voltage, it's just floating about relative to battery -ve.
(most of it relatively low-level - drivers, reverse engineering, lots of disassembly and program analysis for x86/arm/mips/microcontroller code etc. but unfortunately, haven't dipped my hands into hardware things since university)
