DIY Kit MQ-3 Sensor Alcohol Detector Tester Alarm System Soldering Teaching Tranining Kits DC5-7.5V

• Alcohol concentration alarm circuit This circuit is mainly an alarm control circuit formed by the gas sensor group MQ-3.

• When the sensor MQ-3 is in the environment where alcohol vapor exists, the conductivity of the sensor will be the same as the alcohol vapor concentration.

• By measuring the series partial pressure between the sensor and the fixed resistor, the alcohol content in the environment can be judged.

Circuit Description:

This circuit can be powered by 5-7.5V DC power supply, switch S1 is the power switch, resistor R1 and LED D1 are used for power indication.
The internal sensor MQ3 needs to be heated to a certain temperature during operation, so its internal installation.

There is a heating wire, the resistor R4 is the current limiting resistor of the heating wire, and the heating of MQ-3 is normal after power-on.
When MQ-3 does not detect alcohol vapor, its internal resistance is very large.
 
The voltage drop of R3, RW is very low, the voltage of pin 2 of NE555 is lower than the trigger voltage (VCC/3).
Its 3 pin output is high level, D2 is extinguished. The buzzer does not sound and the relay does not move.
 
When MQ-3 detects alcohol vapor, the internal resistance decreases, the voltage of R3, RW rises;
The voltage of pin 2 of NE555 is higher than the trigger voltage;
the 3 pin becomes low level, D2 turns on the light, and the buzzer flows.
 
The current starts to sound, and the electromagnetic coil in the relay energizes to attract the switch.
Thereby implementing the detection alarm function.
The adjustable resistor RW is used to adjust the detection sensitivity.

This circuit uses a second comparator inside the NE555 to detect voltage changes, using its internal trigger to debounce.
The 7 and 5 feet of the NE555 are not used and are left floating.
The output terminal J3 of the relay can be used to control other electrical appliances, such as exhaust fans.
 
When the alcohol concentration exceeds the standard, the exhaust fan is activated.
After the concentration drops, the exhaust fan is turned off to realize automatic control.
Diode D3 is used to eliminate the induced electromotive force generated when the relay coil is turned on and off.
 
The power supply interface can be a DC plug, or the line can be directly at the J2 position.
Pay attention to the positive and negative signs, and the DC plug is internally and externally negative.

(Please kindly noted: we have made a mistake of the LEDs between D2 and D1.  D2 should be Red LED, D1 should be Green LED. Thanks for Stefano's report.)

ICStation doesn't accept any form of pay on delivery. Items used to be shipped after payment. Below are the payment methods we can accept at the moment:

1) Paypal Payment

PayPal is a secure and trusted payment processing service that allows you to shop online. PayPal can be used at icstation.com to purchase items by Credit Card (Visa, MasterCard, Discover, and American Express), Debit Card , or E-check (i.e. using your regular Bank Account). 

We are PayPal Verified 

2)  Bank Transfer / Wire Transfer / T/T

Bank Transfer / Wire Transfer / T/T payment methods are accepted for orders which the total price is up to US$300. The bank will charge about US$50 for the transfer fee if we do the payment in these ways. Feel free to contact us for bank payment details if you need pay via bank.

For other payment method, please contact us at orders@icstation-team.com for more details.