I'm using the switch below as a replacement boor bell switch. The LED requires 12V AC/DC and the switch has change over contacts. Datasheet.
For aesthetic reasons I have to reuse the existing wiring which is only two cores and ~11m long. So the way I see the switch operating is:-
- Normal case - LED lit and current (~10mA) flowing through wires.
- Button pressed - LED off and no current flow.
The above means of operation is possible as you can wire the LED via the switch terminals. Clearly though it's not just a simple case of the traditional pull up resistor on the input pin to a micro controller. I'd like the circuit to be resistant to EMI spikes as well as hardware debounced. I think that I can handle over voltage spikes with a couple of Schottky diodes plus resistor. I looked through a guide on debouncing (Fig.2) and some application specific debounce ICs but they don't seem appropriate for a two core LED style switch. Plus I can't do surface mount. Does this require some form of current detection? An on-board ADC is available. A belt and braces approach will keep my granny happy not having to run to the door every time a car passes by or it thunders.
I think that this might be an original question as others utilise enough cores to separately light up the LED such as:-