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Attached is a picture of a doorbell push button wiring.

What are these circuit components (circled with red) for? Isn't this just a simple mechanical switch?

enter image description here

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user2716454
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2 Answers2

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The door bell units that I am familiar with operate on 24VAC. The wires to the push button switch will be excited with the 24VAC line on one wire and the other wire referenced to the 24VAC-RET return line. For the lowest cost doorbells this switch closes a circuit between the two wires which allows current to flow through the door bell ding-dong mechanism.

Many buttons like this one have an illuminated button feature. The door bell unit allows a small amount of current to flow through the wires to the switch while not activating the ding-dong mechanism. This current is sufficient to light a small LED in the switch button. LEDs operate on a DC current and this needs to be limited to an amount that is safe for the LED. The components that you see in the switch are designed to properly bias the LED without exposing it to excess current or voltage.

Note that in days gone by lighted door bell buttons would use a small incandescent light build designed specifically for operation at 24V. And of course the incandescent bulb is quite happy to operate on an AC voltage unlike the LEDs used today.

Michael Karas
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I will take a SWAG and say that is an illuminated doorbell button using a LED. The black thing is probably a bridge. As far as normal operation just connect the red to white and it will ring. Most of the doorbell buttons I am familiar with are a simple switch.

Gil
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