Corona Protected Automatic Doorbell

A doorbell is an indicator/informative device commonly installed near the entrance door of a home or business. When a guest/tourist hits a button at the entrance gate, the doorbell inside the house/building rings, alerting the owner/occupant of the guest’s/presence. tourist’s As the sars-cov-2 coronavirus spreads by contact with objects already touched by an infected individual, it is dangerous for many persons to continue touching the bell switch. Therefore, coronavirus prevention at the entrance (doorbell switch) is important.

In our suggested project, we build and implement an Arduino-controlled, Corona-protected automatic doorbell that only rings when the user’s/guest’s/hands visitors have been sanitized with hand sanitizer. When someone wants to ring the bell, they must place their hands 3 to 5 centimeters apart in front of the mq3 sensor (this sensor is the heart of our proposed project).

Hardware Required

  • 12v,2A adapter
  • IC-ULN 2003
  • 5V Relay
  • LED
  • Electric Doorbell
  • 220 ohm Resistor
  • Breadboard



MQ3 sensor is a metal oxide semiconductor (mos) type of sensor also referred to as chemiresistors due to its detection based on the alteration of the sensing material when exposed to chemicals (which contains ethanol).

The MQ3 sensor contains a heating element that actually heats the layer of conductive material whose resistance is being measured. When sanitizer scent gets into touch with mq3, resistance changes.

MQ3 sensor output is both analog and digital. Here, we utilize the analog output of the mq3 sensor since a wide range of signal values from 0 to 1023 is delivered, which corresponds to the concentration of alcohol in a sanitizer.


  • Interface Type: Analog & Digital
  • Working voltage: DC 5V
  • Working Current: 150mA
  • DOUT: TTL output
  • AOUT: Analog output
  • Preheat time: Over 20s
  • Detection Range: 0.05 mg/L to 10 mg/L
  • Sensitive to Alcohol, Benzine, CH4, Hexane, LPG, CO
  • High Sensitivity to Alcohol & small sensitivity to Benzine.
  • Digital Out is High or Low based on an adjustable preset threshold,
  • Stable & Long Life.
  • Onboard Power indication
  • The TTL output signal is a low level
  • Analog 0 ~ 5 v voltage output, the higher the concentration, the higher the voltage
  • Fast response and recovery
  • Adjustable sensitivity
  • Dimension: 32mm x 22m x 27mm


ULN2003IC is a driver IC for relays. This IC is utilized when driving high current loads with digital logic circuits such as an operational amplifier, 555 timers, logic gates, Arduino-Uno, and microcontrollers, among others. ULN 2003 is mostly employed to control relays, dc motors, and stepper motors. In the proposed work, this relay driver IC is employed to drive a 5-volt relay.



When a person places his/her hands within 2 to 5 cm of the MQ3 after using hand sanitizer, the MQ3 provides an analog output that drives the interfaced Arduino-Uno to generate a signal at pins 8 and 9. Here, pin-8 is connected to an LED that will light up when the mq3 detects the odor of sanitizer, while pin-9 is connected to an uln2003IC that simultaneously powers a relay that is attached to the doorbell so that it will ring.

If the user or visitor does not use hand sanitizer, mq3 will not generate analog output, and Arduino-Uno and relay will not be driven, hence the bell will not ring.


  • Automatic doorbell installation at the building’s entryway.
  • Use of hand sanitizer must be required for safety From corona.
Circuit-diagram for Corona Protected Automatic Doorbell

Source Code Program

#define MQ3 A0
#define Thresold 420
int value;
void setup() {
pinMode(MQ3, INPUT);
pinMode(8, OUTPUT);
pinMode(9, OUTPUT);
void loop () {
value = analogRead(MQ3);
if ( value > Thresold )
digitalWrite ( 8 , HIGH );
digitalWrite ( 9 , HIGH );
else {
digitalWrite(8, LOW);
digitalWrite(9, LOW);
delay (500);

Circuit Prototype

CLOSER-VIEW-OF-BREADBOARD for Corona Protected Automatic Doorbell
CLOSER-VIEW-OF-BREADBOARD for Corona Protected Automatic Doorbell

Note: We can use a 12V, 1A adapter also, instead of 12V, 2A adapter.


I hope all of you have understood how to design Corona protected automatic doorbell. We MATHA ELECTRONICS will be back soon with more informative blogs soon.

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