This document presents a design for an air flow detector circuit. The circuit uses the variable resistance of an incandescent light bulb filament when exposed to different air flow rates. An op-amp comparator circuit compares the filament resistance to a reference voltage and lights an LED if air flow is detected. The circuit could be used to monitor airflow in applications like electronics cooling, HVAC systems, clean rooms, and laboratory equipment to detect failures or issues.

2. AIR FLOW DETECTOR
Presented To :
Engineer Muhammad Ramiz
Presented By:
Muhammad Arslan Hafeez
Zain Asghar
Abu-Bakar Rasheed
Muhammad Umair Ikram
Hammad Ahmad

3. Introduction
 Explicit airflow detection is essential in many applications.
 High power density electronics are liable and self-destruct when cooling fan failures go
unnoticed.
 Heating and air-conditioning systems often incorporate multipoint monitoring of
ventilation-duct flow.
 Clean room air handling systems with undetected dirty blocked air-filters can ruin
process yield.
 Laboratory fume hoods can contain volatile solvents or toxic reagents making adequate
air turn-over critical to safety.
 In these and similar scenarios , the consequences' of undetected airflow interruption can
range from the merely expensive to the frankly dangerous.
 Therefore it becomes necessary to use some reliable means of airflow detection.
 This is a design for detecting airflow.
 This circuit can give visual for the measurement it can be also used to check whether
there is a airflow in a given space.

4. Components
 Comparator IC (LM339)
 Voltage regulator IC (7805)
 40W Incandescent Bulb Filament
 LED
 9 V DC Battery
 Resistors:
 R1 100 OHM
 R2 470 OHM
 R3 1K OHM
 R4 10K OHM
 R5 20K OHM

5. Incandescent Bulb Filament
 The filament L1 can be made by removing the glass of a 40W
incandescent bulb.
 Caution,We do not touch the filaments of incandescent lamps
by hand.
 The circuit can be powered from a 12 V DC power supply.
 In case the filament is not available, we can use different
resistances to denote the change in resistance across the
filament.
 The glass will have to be removed from L1 without breaking
the filament.

6. Filament as a Bulb
 The glass will have to be removed from L1
without breaking the filament.
 We wrap the glass in masking tape.
 We slowly crank down until the glass breaks,
then remove the bulb and carefully peel back
the tape.
 If the filament has broken, we need another
lamp.

7. IC 7805
 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.

8. Pin Diagram of IC 7805

9. IC LM339
 IC 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.

10. Pin Diagram of IC LM339

11. LED &
RESISTORS We vary the resistances, the brightness of LED
varies.
 When the resistance is high, i.e there is no air
flow, the LED doesn’t glow.
 When resistance is low i.e when air flow is there
the LED glows.
 As we don’t get low resistance in the laboratory,
we use a short circuit with a wire to denote low
resistance.

12. Principle
 Principle of hot wire anemometer is
used in this circuit.
 Resistance of filament changes during
the flow of air and that is compared
with the reference voltage to detect
the air flow.

13. Working
 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.
 We know that heat generated is directly proportional to resistance.
 So, with the flow of air, resistance across the filament varies.
 This variations in the resistance will produce variation of voltage
across the filament (OHM’S LAW).
 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.

14. Applications

15. Industrial Application
 Industrial gas flow measurement.
 Detection of air leakage in
pressurized air systems.
 Air intake of combustion engines.

16. Application in Medical Science
 Spirometers.
 A spirometer is an apparatus for
measuring the volume of air inspired
and expired by the lungs.
 A spirometer measures ventilation,
the movement of air into and out of
the lungs.

17. Future Scope
Wind energy
farms.
Vacuum detector.

18. Circuit Diagram

19. Schematic Capture

20. PCB Layout

21. Air Flow Detector Video

22. Conclusion
 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 high.
 Thus the air flow is been detected and as an output the LED
indicates.