If i connect a switch to the reset pin, can I create an effective way of turning off the Arduino (overnight) without removing its power supply?
It wouldn't really be off, but the I/O pins would be high impedance, and the sketch would not be running. If you just want to stop it doing something (like feeding fish or something) you could just have the code test a pin, and if that pin was in a particular state, stop doing whatever it usually does.– Nick Gammon ♦Jul 4, 2015 at 2:38
If your concern is power consumption, you'd have to see how much of the chip the reset shuts down (and what is consumed by the built-in pullup resistor on the reset itself). There are also ways to shut down nearly everything, until it is woken up again by a pin interrupt. Note that neither will shut down the USB-serial chip and its consumption.– Chris StrattonJul 4, 2015 at 3:09
1The question is, why do you want to do this? If it is to save power, my experiments show that holding the chip in reset is not the most effective way.– Nick Gammon ♦Jul 4, 2015 at 5:10
Wouldn't connecting the switch to the power supply be just as easy? Holding reset will not power down the AVR, nor will it shut down the other parts that are on the Arduino board (voltage regulator, led, usb-to-serial etc.)– GerbenJul 4, 2015 at 19:19
Tests show that connecting Reset to Ground on a Uno reduces the power consumption from 47 mA to 41 mA. So it is hardly "off".
All that would do is stop the currently-loaded sketch running, and save a few milliamps.