This document describes a circuit that can detect air flow using an incandescent light bulb filament. The filament acts as a sensor, with its resistance dropping when air flows over it due to convective cooling. This resistance change is amplified by an LM339 operational amplifier and used to vary the brightness of an LED, providing a visual indication of the air flow rate. The circuit also includes voltage regulators to provide stable power and can be used to detect air flow in industrial, medical, or automotive applications.

1. MINI PROJECT-2
ON
AIR FLOW DETECTOR
NAME REG NO.:-
ANOOP KAMAL MINZ U10EE003
ANUPAM KUMAR U10EE004
BISHWARUP MUKHERJEE U10EE006

2. Abstract:-
This circuit can give a visual indication of the rate of air flow. It can be also
used to check whether there is air flow in a given space.
The filament of a incandescent bulb is the sensing part of the circuit. When
there is no air flow the resistance of the filament will be high.
When there is air flow the resistance drops , because the moving air will remove
some of the heat generated in the filament.
This variations in the resistance will produce variation of voltage across the
filament.
These variations will be picked up by the opamp (LM339) and the brightness of
the LED at its output will be varied proportionally to the airflow.

3. CIRCUIT DIAGRAM:-

4. Live circuit

5. Component required:-
S NO. TOTAL QTY DISCRIPTION
R1 1 100 Ohm 1/4W Resistor
R2 1 470 Ohm 1/4W Resistor
R3 1 10k 1/4W Resistor
R4 1 100K 1/4W Resistor
R5 1 1K 1/4W Resistor
C1 1 47uF Electrolytic Capacitor
IC1 1 7805 IC
IC2 1 LM339 IC
L1 1 filament
D1 1 LEDMISC1Board, Wire,
Sockets for ICs, etc.

6. IC 7805
7805 is a voltage regulator integrated circuit. It is
a member of 78xx series of fixed linear voltage
regulator ICs. The voltage source in a circuit may
have fluctuations and would not give the fixed
voltage output. The voltage regulator
IC maintains the output voltage at a constant
value. The xx in 78xx indicates the fixed output
voltage it is designed to provide. 7805 provides
+5V regulated power supply. Capacitors of
suitable values can be connected at input and
output pins depending upon the respective
voltage levels.

7. IC LM339
LM339 is a comparator IC with four inbuilt comparators. A
comparator is a simple circuit that moves signals between the
analog and digital worlds. It compares two input voltage levels
and gives digital output to indicate the larger one. The two
input pins are termed as inverting (V-) and non-inverting (V+).
The output pin goes high when voltage at V+ is greater than
that at V-, and vice versa. In common applications, one of the
pins is provided with a reference voltage and the other one
receives analog input from a sensor or any external device. If
inverting pin (V-) is set as reference, then V+ must exceed this
reference to result in high output. For inverted logic, the
reference is set at V+ pin.

8. WORKING OF IC LM399

9. 100k chip resistor
Specifications of MDST-1-100K-W-ESA-N-1-N-Y
Track
Resistan
ce
100kohm
Track
Taper Linear
No. Of
Turns
1
Power
Rating
200mW
No. Of
Gangs
1
Svhc
No SVHC (18-Jun-2010)
Resistor
Element
Material
Variable Rotary
Approva
l
Categor
y
VDE
Potentio
meter
Mountin
g
Panel
Rohs
Complia
nt
Yes
Lead
Free
Status
/ RoHS
Status
Lead free / RoHS
Compliant

10. APPLICATION:-
• Industrial gas flow measurement
• Leak detection in pressurized air
systems
• Spirometers
• Air intake of combustion engines

11. CONCLUSION
 Thus, the circuit can give a visual indication of the rate of air
flow.
 It can be also used to check whether there is air flow in a
given space.
 The filament of an incandescent bulb is the sensing part
of the circuit.
 When there is no air flow the resistance of the filament
will be low.
 Thus the air flow is been detected and as an output the
LED indicates.

12. BIBLIOGRAPHY
 http://www.wikipedia.org/ WIKIPEDIA.
 http://electronicsforu.com.asp ELECTRONIC FOR YOU.
 http://www.circuit-projects.com/ CIRCUIT PROJECT.
 http://www.aaroncake.net AARON CAKE.
 http://electroschematics.com/ ELECCTRON
SCHEMATICS.