digital-logicinputswitchestoggle switch
I want to connect a switch to a digital input on a logic board and make it so that the input goes high when the switch is pressed. I'll be using a SPDT switch:
Should I connect the digital input to COM, GND to NC, and VCC to NO?
Or could I connect VCC to COM and the digital input to NO? (this would leave the digital input "floating" when the switch isn't pressed, but is that necessarily a bad thing?)
To get at your question about if you can plug power directly to the pin with no resistor and have it always be high... yes, that does work.
When you have your microcontroller set to input mode you can treat the pin like there is a very large resistor inside. So using ohms law, V/R=I with V=3.3 and R=very large, lets say 10megohm gives you a current of 0.33 micro amps. The inputs are designed to act like such a high impedance so that it has a very small effect on anything externally.
What you need is a pull-up resistor.
The Arduino whebsite has a nice tutorial (with software) on using a pushbutton.
We connect three wires to the Arduino board. The first goes from one leg of the pushbutton through a pull-up resistor (here 2.2 KOhms) to the 5 volt supply. The second goes from the corresponding leg of the pushbutton to ground. The third connects to a digital i/o pin (here pin 7) which reads the button's state.
Best Answer
You want to use the first option: connect the digital input on the micrcontroller to COM, GND to NC (1T), and VCC to NO (2T), except use an resistor, e.g. 4.7K, between VCC and the NO (2T) terminal. Usually not a good idea to connect VCC directly to an input pin on the micrcontroller -- for example, if it became a digital output for some reason and was at GND level, you would have a nasty short.