NP2 - Wired Button 15ft+ away fires randomly - Page 2 - Netduino Plus 2 (and Netduino Plus 1)

Here's the current working circuit... Maybe somebody can give me some idea's on why it works, and if any changes may be needed...

Ever been to the circus?

If so, you've probably seen the (wo)man walking on a rope. A simple false step and the acrobat would die.

BUT...

Those (wo)man isn't stupid, and uses a long pole as aid. Probably without the pole a fall would be far easier.

So, what?

If you notice, when the (wo)man walks (s)he shakes a little, because the continuous balance control. However, even being a little shake, it might be fatal for the overall stability. Consider that the rope will move also under the acrobat shaking...

When the (wo)man holds a long pole, you'll see that *the pole* is incredibly stable. Although maybe the acrobat shakes a little, the pole looks as it were "fixed" somewhere...kinda magic!

That's because inertia/momentum...

Stick to physics, but to the electric branch.

If you re-read my post above (the very first answer to this thread), a long wire acts as an antenna and is far more "addict" to chase any noise, spike, electrostatic discharge happens in the nearby. That reflects on the circuit, by triggering false state-toggles on the input.

I'd also add that a *strong* discharge close to the button wires may even damage the digital input.

Where the discharges were the acrobat shaking, the capacitor would be the "pole". A capacitor *IS* the equivalent to an inertial part, that is actually a "tank" of electron. By the way, if you think to an hydraulic system, a tank would be something gets "smooth" the flow. A river is flowing fast, but when the water accumulates into a lake then gets way smoother.

So, yes...your wire is still capturing discharges. Unless you follow my recommendations on using a shielded cable, the "chasing" is unavoidable. However, the capacitor comes in your aid, by "smoothing" any voltage level spike.

About your circuit (I mean the Arduino's).

It's correct to wire the button toward ground. Although the logic will be reversed (push=low), the noise immunity is better. This pattern would help in other context, but that's off *this* context.

The resistor to +3.3V is also correct. Also let's assume that 1k is an acceptable value.

The resistor in series to the capacitor is not mandatory, but it's a good choice. I wouldn't take its value above your's: just an hundreds of Ohms to limit the capacitor discharge. A too high value would also limit the capacitor benefit.

The 100nF cap...well, that's more a challenge: it's not so "powerful"!

Just a *very* rough value: R*C = 1k * 100n = 1E-4, that is 100 microseconds. Let's say that the cap is able to smooth pulses whose duration is around 100us...a longer pulse/discharge would pass through.

Personally I'd use a bigger cap: 10uF is 100 times more, and it should be big enough to cut almost any reasonable spike over the wire. However, a pushbutton is way longer than the RC effect so your goal will be reached without any problem.

To close...

In my first answer I told you to try with a simple shielded cable: very easy and no extra parts. I also alerted on the possibility to add an RC filter, but I would have avoided such a tedious explanation unless mandatory.

Here it is!

Good luck.

Mario