This document describes an air flow detector circuit project created by a group of 12 students. The circuit uses a hot wire anemometer principle to detect changes in air flow by measuring the resistance of a filament. When air flows over the filament, its resistance drops and the signal is sent to a comparator IC which then adjusts the brightness of an LED to indicate the level of airflow. The document provides details on the components used, circuit operation, and potential applications of the air flow detector circuit.

1. GROUP4 | measurement project | December 26, 2017
Air flow detector
Under supervision:
DR Mohammed Anwar

2. Table of Contents
GROUP4 | measurement project | December 26,
2017
Contents
introduction_____________________1
project requirements _____________2
Component description ___________4
Genral measurement system_______5
Circuit Operation _______________6
project application _______________7
Group information _______________8
References ____________________9

3. GROUP4 | measurement project | December 26,
2017
1
INTRODUCTION
Explicit airflow detection is essential in many applications:
 . High power-density electronics are liable to overheat
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 for airflow detection.
 This circuit can have used to check whether there is
airflow in a given space.
 This is done by LED light when airflow Passing
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.

4. GROUP4 | measurement project | December 26,
2017
2
PROJECT REQUIREMENTS
Resistance
-100 Ω
-470 Ω
-10 KΩ
-1 KΩ
Variable resistance
100 KΩ
Capacitor
47 µf
Max. Volt 15 v
ICS:
-IC 7805 W
-IC LM 339
Battery 12 V DC
Bread board

5. GROUP4 | measurement project | December 26,
2017
3
Switch on/off
LED
Probes
Small fan
Incandescent bulb 40 watt

6. GROUP4 | measurement project | December 26,
2017
4
COMPONENT DESCRIPTION
- IC 7805
- IC LM339
IC 7805 is a 5V voltage regulator that
restricts the
voltage output to 5V and draws 5V
regulated power supply.
The maximum value for input to the
voltage
regulator is 35V. It can provide a
constant steady voltage flow of 5V for
higher voltage input till the
threshold limit of 35V
A LM339 is a small scale integrated circuit
that contains 4 comparators on a single chip.
The LM339 is not universal as most
operational amplifiers are. The comparators
on the chip do not amplify with feedback,
rather only switch state (+V, Ground) on their
output. The benefit to the
"locked" behavior is some of
the smallest power drains a
TTL chip can provide and fast
switching speeds

7. GROUP4 | measurement project | December 26,
2017
5
GENRAL MEASUREMENT SYSTEM
Sensor information: Resistive Temperature Detector (RTD)
Tungsten
filament
Deflectio
n Bridge
Amplifier
Sensors Signal
conditionin
g
INPUT
IC LM339
OpampLED
Signal ProcessingData
presentation
OUTPUT
R
v V
V

8. GROUP4 | measurement project | December 26,
2017
6
CIRCUIT OBERATION
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. 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

9. GROUP4 | measurement project | December 26,
2017
7
PROJECT APPLICATION
1- air intake of combustion engines
The air mass information is necessary for the engine control unit (ECU) to balance and deliver
the correct fuel mass to the engine. Air changes its density as it expands and contracts with
temperature and pressure There are two common types of mass airflow sensors in use on
automotive engines. These are the vane meter and the hot wire.
a) Vane meter
The VAF (volume air flow) sensor measures the air flow into the engine with a spring
attached to a variable resistor
b) Hot wire
2- leak detection in pressurized air systems
3- spirometer
measures airflow. By measuring how much air you exhale, and how quickly you exhale, can
evaluate a broad range of lung diseases
4- industrial gas flow measurement
 Decision support in monitory operation as a
periodic condition
-Data collectors
-Inspection systems

10. GROUP4 | measurement project | December 26,
2017
8
GROUP INFORMATION
Team 4: (Air Flow Measurement and Detection Circuit
Assayyid Fathy Khalaf1)
Sayyid Khairy Salama2)
Nour Sayed Kamal3)
Kareem Fathy Mohammed4)
Assem Hussien Abdulrahman5)
Mohamed Osama Alsemsam6)
Yasser Mohamed Gehad7)
Mohamed Kamel Saleh8)
Shady Heshmat Amin9)
Mahmoud Ahmed Ibrahim10)
Badr Sayed11)
Mohamed Salah Ragab12)

11. GROUP4 | measurement project | December 26,
2017
9
REFERENCES
http://en.wikipedia.org/wiki/Mass_flow_sensor
 http://en.wikipedia.org/wiki/Air_flow_meter.
 http://www.circuitstoday.com.
 http://en.wikipedia.org/wiki/78xx
 http://electronicsforu.com.asp
ELECTRONIC FOR YOU
http://www.circuit-projects.com/
CIRCUIT PROJECT
lectures for: DR:M-Anwr &
DR:M-Abdallah &DR:M-Atia