Flashing LED Doorbells

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Doorbell Circuit
When the push switch is operated - the buzzer will sound and the LEDs will begin to flash. For the hearing members of the household - the buzzer acts as a regular doorbell. It also reassures the visitor that the doorbell is working.

db1.png

Groups of up to three LEDs may be connected to the output pins of gates 3 & 4. Each group must have its own series resistor. And the value of the resistor depends on the number of LEDs in series with it. You don't have to use the two outputs. You can choose to use just a single group of LEDs - connected to a single output pin. If you do use both outputs - you can make one large display. Or you can have two smaller displays - each in a different room.

The speed at which the LEDs flash is controlled by the values of R3 & C2. With the values given in the diagram - the LEDs will flash at about the rate shown. Replace R3 with a 1Meg variable resistor - and you can adjust the speed of the flash. However - if you make it too fast - the flash effect will be lost - and the LEDs will appear to be on all the time.
 

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