Jan 202021
 

Doorbell for deaf people

Doorbell for deaf people. When a deaf person is alone in a house, it would be very difficult to realize that someone is knocking on the door without any visual warning signal.

This circuit, doorbell for the deaf, shows a visual warning that allows the deaf person to realize the situation in which it is.

The circuit is connected to a doorbell system that works with direct current (DC) as shown in the diagram, where the actual sound signal is a buzzer.  The circuit is not connected to the common alternating current (AC) doorbell system normally found in houses.

How the doorbell for deaf people circuit works?

The main component for the Doorbell for the deaf people circuit is  the CMOS 4001 integrated circuit, which has four two input NOR gates. IC1a gate, capacitor C1 and resistor R3 form an oscillator. This oscillator is enabled when the IC1b gate has a high voltage level at one of its inputs.

Doorbell for Deaf People Circuit using LEDs

The “enable” signal for IC1b is a low voltage level at the junction point of capacitor C2 and resistor R2. Every time a visitor presses the momentary contact switch SW, capacitor C2 is discharged through diode D2 and resistor R1. It is at this time that the signal that enables the oscillator is obtained.

When the oscillator is running, IC1a output goes from high to low continuously for a time that depends on the values of R2 and C2. The IC1a output signal is sent to the two inputs of each of the gates IC1C and IC1D, which are wire as a two-input NAND gate.

CD4001 - Quad 2-input NOR Gate

CD4001 – Quad 2-input NOR Gate

IC1C and IC1D have, at their outputs, the voltage levels that turn ON and OFF the LEDs that visually notified that a person is knocking at the door.

LEDs will blink for about 20 seconds, that means the visual signal will be active for much longer than the sound of the buzzer. If you want to increase or decrease the time of activation of the LEDs, you can change the values of R2 and C2.

List of circuit components

  • 1  4001B, 4 2-input NOR gates integrated circuit (IC1)
  • 1  2.7K resistor (R1)
  • 1  330K resistor (R2)
  • 1  470K resistor (R3)
  • 1  470nF capacitor (C1)
  • 1  47uF electrolytic capacitor (C2)
  • 2  1N4148 diodes (D1, D2)
  • 6  common red LEDs (D3, D4, D5. D6, D7, D8)
  • 1  buzzer (BZ)
  • 1  alkaline 9 volt battery (B)

The doorbell for the deaf circuit is powered by a 9 volt battery. It can also operate with a supply voltage of 9 volts connected to the network (110/220VAC). This circuit has a negligible consumption when it is not active.

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