playing a bit around I have connected 3 of 1kOhm resistances in series between the 5V pin and the GND pin of the Arduino. When I tap with the voltmeter (Kethley 2000 multimeter) I get 1.6V after the first resitance (starting from GND), 3.3V after the second and 5V after the third and last. But when I proceed to measure the current in it, I don't get the value I would expect! By tapping the amperemeter (Kethley 2000 multimeter) I get a current of 2.5mA. But what I would expect is (V/R=I) 1.6/1000=0.0016 i.e. 1.6mA? What am I not understanding from the Arduino, or just from life ?
2,5mA, that is exactly 5V / 2k = 5V / (1k + 1k). Aka, your putting the resistor meter over one of the resistors. But with that, you short out that resistor like it's not even there.
Aka, you measure voltage OVER something and current TROUGH something. So in order to measure correctly you need to break the circuit somewhere and put the meter in series in that break
septillion:
2,5mA, that is exactly 5V / 2k = 5V / (1k + 1k). Aka, your putting the resistor over one of the resistors. But with that, you short out that resistor like it's not even there.
EXCELLENT DEDUCTION!!!!
ivino, Be very careful whenever the meter is set to measure current, and make sure you know how to measure current. The meter creates a short circuit (nearly zero-Ohms) and you can damage your circuit-under-test, or you can blow the meter (or the fuse in the meter).
In the real world, we only occasionally measure current. I work in electronics and I measure voltage every day. I measure resistance once in awhile. But I can't remember the last time I used my multimeter to measure current. (However, I "cheat" because the power supply on my bench indicates voltage & current, so I can see the current when I'm using the bench supply.)
DVDdoug: In the real world, we only occasionally measure current.
Just don't forget it's there, it can be extremely useful to find problems that aren't obvious when measuring only voltage.
A few weeks ago I discovered that the brownout reset was being triggered in one of my projects. It was difficult to notice that just measuring voltages, it became more obvious when I measured the microcontroller's supply current and saw it spike up to a couple hundred microamps, instead of the constant 6 uA I was expecting.
