The author had a problem: the neighbors had exactly the same type of doorbell as he did (actually a 50 Hz buzzer), so it wasn’t always clear who needed to answer the door. To avoid confusion, the author augmented the existing doorbell with a wireless model — a reasonably inexpensive option at current prices. All that was necessary for this was to arrange for the existing button and wiring to also actuate the wireless doorbell.
The author opened up the button enclosure of the wireless doorbell and used a multimeter to find out which set of contacts were closed when the button was pressed. This is where the relay output should be connected (see the schematic diagram). The circuit is virtually self-explanatory: when the existing doorbell button is pressed to actuate the buzzer, the voltage is rectified by the bridge rectifier and regulated at 5 V by the 7805. This voltage drives the relay directly, causing the switch in the wireless doorbell button to be shorted. As a result, along with the buzzer, a sizeable Big Ben chime indicates that someone is at the door.
Now the author just hopes that his neighbor doesn’t copy his idea.
A multimeter is a measuring instrument that can measure multiple electrical properties. A typical multimeter can measure voltage, resistance, and current, in which case it is also known as a volt-ohm-milliammeter (VOM), as the unit is equipped with voltmeter, ammeter, and ohmmeter functionality. Some feature the measurement of additional properties such as temperature and capacitance.
