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My washing machine is equipped with a capacitive start button. A "button" is marked with paint on the plastic front and on the backside of the panel there is a spring extruding from the control PCB, pressing against the inside of the plastic panel. I would like to trigger this using an Arduino. While searching for answers I've been trying to use a metal foil, grounded through a relay to trigger the button, but inconsistent results. Could I connect directly to the spring, in any configuration, to trigger this button in a simple way?

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  • \$\begingroup\$ Are you sure it's capacitive, can you turn it on for instance with a plastic kitchen utensil? \$\endgroup\$ – PeterJ Dec 18 '15 at 13:33
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    \$\begingroup\$ A plastic object will not trigger it, but my finger will from a distance of a few millimeters. \$\endgroup\$ – Chrille Dec 18 '15 at 14:38
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I believe it is worth trying to connect directly to the spring: you may get more consistent triggering (I would expect it, but no guarantee).

I'd use a small ceramic capacitor instead of a direct connection though, to protect the capacitive sensor from DC and 50 Hz AC currents which may appear in your circuit. It should be anywhere in 1-100 nF range, one terminal connected to the spring, the other one to your relay. I actually expect such capacitor to be present on the PCB in series with the spring, but extra protection can't hurt.

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