Here’s an interesting circuit of a wireless door bell/buzzer for electronics students and hobbyists. The circuit is a short-range radio-frequency (RF) tone generator realized with the help of a cheap 433MHz RF transmitter & receiver module pair commonly available from almost all online electronics component shops. Apart from the RF modules, only a 555 timer chip is needed to complete the project. Let’s see the secretes!
The two-part circuit diagram (transmitter & receiver) shown below hardly needs an explanation as it’s extremely simple and straight forward. Just follow the well-annotated schematics to build your own prototype on small pieces of veroboard or customized circuit boards. Only one minor drawback of the design is that it’s not a melody-door bell but a simple one with a constant high-pitched (ear-splitting) tone output to draw the quick attention of someone in the neck of the woods.
The transmitter and receiver circuits can be powered from 6V dc supply (1.5VAA cell x4). It would be better to power the receiver part from a series of 4 standard AA dry cells, while for the transmitter part try to use 4 Energizer E90 alkaline cells in series. Further, to get optimum performance, attach quarter-wave length stiff wire antenna (straight or coiled) to both the 433MHz Tx and Rx RF modules.
I do this for the joy of experimenting & learning, and a bit of further experimenting will hopefully get you more from this basic concept. Unfortunately, it’s observed that the receiver makes some chirps in response to other 433MHz transmitters in its close proximity. Fortunately, an improved version of the wireless door bell is now under development, and sure it will reach at your desktop within a few weeks.