DIY Doorbell Memory Circuit: Build Your Own 3V Tale-Tale

Description

If you anticipate an important guest but require a brief departure, a digital chime recollection system can prove valuable, allowing you to ascertain whether someone activated the bell during your absence. Naturally, you cannot determine if it was the expected visitor who arrived, however, a call to the mobile device of the concerned individual can swiftly provide that information. A chime recollection system can also eliminate the need to proceed to the entranceway (if you reside upstairs) when you suspect the bell has sounded but are uncertain. Furthermore, if purchasing one is not feasible, you can, of course, construct one yourself! Continue reading to discover how.

Circuit diagram:

Circuit description:

Only a limited number of electronic components are necessary to build a functional notification device with an LED displaying whether someone pressed the doorbell’s button. How many times have you considered you heard your doorbell while watching television in the evening? The familiar ‘ding-dong’ sound occurs far too frequently, especially during numerous advertisements that now disrupt us at the most inconvenient moments, reminding us that the engaging film we are watching is merely a fabrication.

A glance at the LED of the chime recollection system will reveal whether you must go to the door or attempt to evade the advertisements by switching to a different channel. Or, if you’re expecting someone but must undertake a quick trip to the neighbors to borrow a few beverages for the event, it can be advantageous to determine whether your visitor has already arrived while you were out. If so, you can always contact them on their mobile device to admit that you hadn't adequately prepared for the anticipated visit.

The circuit is as uncomplicated as it is effective. It is connected in parallel with the bell and powered by a 3-V power source formed by two 1.5-V penlight batteries connected in series. The chime recollection system draws such a minuscule amount of current that a set of batteries will endure for several years in typical operation. The circuit operates as follows. When the power supply voltage is switched on with switch S1, capacitor C1 (initially discharged) prevents transistors T1 and T2 from conducting. LED D2 remains off, and the memory is armed.

When the doorbell button is pressed, the memory circuit receives an AC or DC voltage via diode D1, depending on the type of doorbell. It can handle either type. Transistor T1 thus receives a base current, so it begins to conduct and drives T2 into conduction. The LED illuminates as an indication that the doorbell has been activated (i.e., energized). The combination of transistor T2 and resistor R3 maintains T1 conducting after the bell voltage disappears (when the button is no longer pressed).

The memory remains in this state until switch S1 is opened. This switch, therefore, also functions as a reset switch as well as a power switch. The circuit can be assembled compactly on a small piece of perforated prototyping board, so it can be fitted into practically any model of doorbell. The transistors can be replaced by other, equivalent types as long as you utilize a combination of NPN and PNP types.