Smoke, Alcohol and LPG-Detection Alarm
Presented
here is a circuit for raising an alarm on detecting smoke or LPG
cooking gas leakage, or even alcohol vapours in breath. This is achieved
by using a basic unit with different sensors for smoke, LPG and
alcohol. So, different alarms can be made by simply changing the input
sensor.
Circuit and working
Fig. 1 shows circuit diagram of the smoke alarm. The basic unit employs dual op-amp LM358 (IC1), transistor T1 and timer NE555 (IC2), configured in astable mode. Selection of MQ* sensor is based on the purpose for which the alarm circuit is being designed. For the smoke alarm circuit, you will need MQ2 sensor. Similarly, for detection of alcohol, MQ3 sensor is used, while MQ6 sensor is used for detecting LPG cooking gas.
MQ* sensor has six pins. Heater filament, between pins H-H, is directly connected to 5V and ground. Two sets of input/output (I/O) pins A-A and B-B are present. Select any one set for input to the basic unit. Arrangement of pins is shown in Fig. 1.
IC1
is wired in the non-inverting comparator mode. The reference voltage is
applied to inverting input (IN1-) and the voltage to be compared is
applied to non-inverting input (IN1+). Whenever voltage to be compared
(IN1+) goes above reference voltage (IN1-), output of the op-amp swings
to high, and vice-versa. The alarm circuit is built around NE555. The
frequency of the astable multivibrator is dependent on the values of
resistors R4 and R5, and capacitor C2.
After connecting to 5V supply, wait for about ten seconds for the filament to heat properly. Adjust 10k potmeter (VR1) till the alarm stops sounding.
Under normal conditions (that is, no fumes from LPG or no alcohol in breath near MQ*), output of IC1 at pin 1 remains low. As a result, transistor T1 does not conduct, which makes pin 4 of IC2 low. It keeps timer NE555 on reset. There is no output at pin 3 of IC2, and no sound comes out of the speaker.
On the other hand, when there are fumes from LPG, or there is alcohol in breath near MQ*, output of IC1 at pin 1 goes high. As a result, transistor T1 drives into saturation and its emitter goes high. Pin 4 of IC2 also goes high. The timer goes into astable mode, producing pulsed wave at output at pin 3 of IC2, which is coupled to speaker LS1 through coupling capacitor C4, and an alarm is set on.
Construction and testing
An actual-size, single-side PCB for the alarm is shown in Fig. 2 and its component layout in Fig. 3. Enclose the PCB in a suitable box, in such a way that fumes can circulate near MQ* sensor easily. Ensure proper wiring to avoid any errors. Before using the circuit, use MQ3 sensor to verify test points given in the table.
 |
Circuit and working
Fig. 1 shows circuit diagram of the smoke alarm. The basic unit employs dual op-amp LM358 (IC1), transistor T1 and timer NE555 (IC2), configured in astable mode. Selection of MQ* sensor is based on the purpose for which the alarm circuit is being designed. For the smoke alarm circuit, you will need MQ2 sensor. Similarly, for detection of alcohol, MQ3 sensor is used, while MQ6 sensor is used for detecting LPG cooking gas.
MQ* sensor has six pins. Heater filament, between pins H-H, is directly connected to 5V and ground. Two sets of input/output (I/O) pins A-A and B-B are present. Select any one set for input to the basic unit. Arrangement of pins is shown in Fig. 1.
 Fig. 1: Circuit diagram of the alarm circuit |
 |
After connecting to 5V supply, wait for about ten seconds for the filament to heat properly. Adjust 10k potmeter (VR1) till the alarm stops sounding.
Under normal conditions (that is, no fumes from LPG or no alcohol in breath near MQ*), output of IC1 at pin 1 remains low. As a result, transistor T1 does not conduct, which makes pin 4 of IC2 low. It keeps timer NE555 on reset. There is no output at pin 3 of IC2, and no sound comes out of the speaker.
On the other hand, when there are fumes from LPG, or there is alcohol in breath near MQ*, output of IC1 at pin 1 goes high. As a result, transistor T1 drives into saturation and its emitter goes high. Pin 4 of IC2 also goes high. The timer goes into astable mode, producing pulsed wave at output at pin 3 of IC2, which is coupled to speaker LS1 through coupling capacitor C4, and an alarm is set on.
 Fig. 2: Actual-size PCB pattern of the alarm circuit |
 Fig. 3: Component layout of the PCB |
Construction and testing
An actual-size, single-side PCB for the alarm is shown in Fig. 2 and its component layout in Fig. 3. Enclose the PCB in a suitable box, in such a way that fumes can circulate near MQ* sensor easily. Ensure proper wiring to avoid any errors. Before using the circuit, use MQ3 sensor to verify test points given in the table.
No comments:
Post a Comment