does anyone foresee a problem with using a looooooong wire, specifically, same diameter as hookup wire, but 20m long, dual core with a switch at the end, connected the standard switch way 5v >> arduino pin >> 10k resistor >> gnd?
if a problem is foreseen, how would i go around fixing it!
kelvinmead:
does anyone foresee a problem with using a looooooong wire, specifically, same diameter as hookup wire, but 20m long, dual core with a switch at the end, connected the standard switch way 5v >> arduino pin >> 10k resistor >> gnd?if a problem is foreseen, how would i go around fixing it!
Not really a problem with just a manual switch. Switch bounce may be a little longer then normal but that can be handled in software as always. Wouldn't harm to also wire a .1ufd cap from the input pin to ground.
Lefty
magic! thanks!
You don't say what will bring the pin high.
Preferable would be a 4.7K pullup to 5V located at the arduino input, with the switch connecting the pin to Gnd when closed.
kelvinmead:
does anyone foresee a problem with using a looooooong wire, specifically, same diameter as hookup wire, but 20m long, dual core with a switch at the end, connected the standard switch way 5v >> arduino pin >> 10k resistor >> gnd?
20m is nothing for a switch.
Transmission of data at MHz frequencies? Yes. A switch...? No problem at all.
out of interest, what would be too long... i suppose the resistance of the wire before the interference?
but 100's of metres, 1000's of metres?
Move R1 between S2 and +5, with D2 connected between R1 and S2. Then if something happens at you switch or to the wire, you are not shorting +5 to Gnd, you are only connecting the pin to Gnd.
The how long depends on the wire+switch+connectors resistance.
You need D2 to go below 1.5V (0.3 x Vcc from section 29 of the datasheet).
Using Ohms Law: Vout = 5V x Rwire/(R1 + Rwire)
Solving for Rwire = 1830 ohm for Vout to be 1.4V
(with R1 = 4.7K, which also limits the current out to the switch to ~1mA - vs unlimited as you have it drawn)
kelvinmead:
out of interest, what would be too long... i suppose the resistance of the wire before the interference?but 100's of metres, 1000's of metres?
Here's a table of Ohms per kilometer based on wire gauge:
The Arduino recognizes "HIGH" at about 2.5V so you can lose 2.5V in the wire to the switch (and back again to the Arduino). Assume a current of a couple of milliamps, the rest is Ohms law.
Let us know the max distance for your wire...
High is >0.6V x Vcc, so 3V for a 5V system.
kelvinmead:
out of interest, what would be too long... i suppose the resistance of the wire before the interference?but 100's of metres, 1000's of metres?
You could go from Bristol to London IF your wire is thick enough 
The limitation would be the cost of that much copper!
