I would like to extend two wires (digital input and gnd) for a momentary button to a distance of ~50cm. Would noise that these wires pick up likely affect the quality of Vcc and Gnd on the Arduino board it is connected to? The board has a sensor that requires no more than 50mV ripple on the supply. Should I worry?
If you use a relatively low value of pullup resistor (1 K or so) on the input and twist the wire pair together, noise should not be a problem.
No, don't worry. For good measure, maybe put an extra cap on the power right next to the sensitive sensor.
Typical causes of supply noise are:
Crappy supply with insufficient output filtering
Switching significant loads with insufficient bypass caps, insufficient supply, or inductive loads (particularly without countermeasures, though inductive loads can be hard to make not-noisy)
Long wires can cause noise on signal lines, but a pushbutton is not sensitive, and 50cm isn't long. Maybe you'll need a stronger pullup than the internal one, but 50cm is pretty short...
Thank you for the replies.