LED as a switch?

[higgenkreuz_007]

Hello all,

I cannibalized a non-working Ooma telo the other day as I wanted to see how they implemented the switches on the board. There are no mechanical switches, the individual switches are illuminated by an LED that is underneath the panel and the circuit reacts when the user covers/touches the button.

From what I can tell these are just simple LEDs. I have heard of photo resistors but these are clearly not that.

Does anyone know what these things are and how they work? They seem to be a neat alternative to physical momentary switches bit I am at a loss to understand how they work.

I uploaded a picture of the panel as well as the board that's sitting underneath it.

Thanks.

[er_name_not_found]

Maybe a capacitance switch

[BitSeeker]

Yes, a capacitive touch switch. The LED is just for illumination. You can get similar switches for Arduino projects. Just Google "Capacitive Touch Switch" or "TTP223". It works by detecting the change in capacitance when a finger is placed near or one the pad.

[higgenkreuz_007]

Oh yes, I can actually see a connection going from each "pad" that houses the LEDs. So a capacitance switch does not require an actual physical contact? Like, physical proximity would do it as well? Pretty good.

[killzone_kid]

you can technically use LED as photo sensor but using it as an appliance control would be strange as it might work at day time but what you gonna do at night where there is no good light source

[Grumpy_Mike]

@killzone_kid

but using it as an appliance control would be strange as it might work at day time but what you gonna do at night where there is no good light source

Well you can operate it so it generates its own light. Especially if you use an IR LED that you won't see.

See my tutorial and video on this at:-
LED Sensing

[killzone_kid]

Pretty neat

[ShermanP]

When my Telo stopped working, it turned out to be the power supply - the two output capacitors.