What is inside a cheap wireless doorbell?

There are some very cheap wireless door bells available on Ebay, often shipping from sellers in places like China and Hong Kong.

I had one of these cheap door bells fail on me recently and rather than just put it in the bin I decided to open it up and see what was inside. It is a pretty simple piece of equipment so not much of a tear-down but below is what I found.

The door bell opened up

The door bell opened up

Opening up was just a case of removing one screw inside the battery compartment and then easing and unclipping.

In the picture above the small speaker can be seen inside the front cover along with a small curved pcb which contains the three LEDs which flash through the front of the doorbell when it rings.

The other half of the plastic case has the main circuit board mounted at the top with the double AA moulded battery holder below.

The printed circuit board

The printed circuit board

Moving on to the printed circuit board there are a couple of diodes, a couple of transistors, some resistors and both ceramic and electrolytic capacitors. In the centre can be seen a silver cased crystal and at the top a red adjustable inductor. There is a switch on the right which as well as switching the door bell on and off has a melody select position.

The printed circuit board has two integrated circuits. The first is the plainly on view in the picture, this is a TC4069UBP Hex Inverter. The second IC is mounted on its own mi nature pcb which is then soldered vertically into the main pcb, this can be just seen at the bottom of the picture.

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