This document describes a moisture sensor circuit that uses an operational amplifier (IC 741) and transistors (BC547) to indicate the presence of moisture. When moisture is detected by the sensor, the op-amp changes states and turns on a green LED while turning off a red LED. The circuit diagram and components used are shown. It then explains how the op-amp acts as a voltage comparator and how the transistors are used to switch the LEDs on and off depending on the sensor reading. Finally, some applications of moisture sensors are listed such as in chemical processing, weather monitoring, and greenhouse humidity control.

1. MOISTURE SENSOR
Presented by
Khurram shahzad Abbasi
Zia ur Rehman
Mohsin Javid
Presented to:
Engr . M.Tufail

2. INTRODUCTION
CIRCUIT DIAGRAM
COMPONENTS USED
WORKING
APPLICATIONS

3. INTRODUCTION
This circuit indicates presence
of moisture in a place due to rain
or spilling of water .
Green LED lights when there is
a moisture and red LED lights
when there is no moisture

4. CIRCUIT DIAGRAM

5. COMPONENTS USED
 IC 741
 BC547
 10 uF
 41k
 10k
 1k
 470R
 LED’s
 DC voltage source
 Touch pad

6. IC 741
 As the name implies it is an operational
amplifier.
 OPAMPS can amplify both AC and DC
signals.
 The 741 has two inputs and one output.
The difference between these two inputs
is amplified and that is what appears at
the output.
Some of the general characteristics of
the IC version are:
 High gain, on the order of a million
 High input impedance, low output
impedance
 Used with feedback, with gain
determined by the feedback network.

7. BC547
 BC547 is an NPN bi-polar
junction transistor. A
transistor, stands for transfer
of resistance, is commonly
used to amplify current. A
small current at its base
controls a larger current at
collector & emitter terminals.

BC547 is mainly used for
amplification and switching
purposes. It has a maximum
current gain of 800. Its
equivalent transistors are
BC548 and BC549.

8. CONT’D……
The transistor terminals require a fixed DC
voltage to operate in the desired region of its
characteristic curves. This is known as the biasing.
 For switching applications, transistor is biased so
that it remains fully on if there is a signal at its
base. In the absence of base signal, it gets
completely off.

9. WORKING OF CIRCUIT:-
IC1 (741) is used as a voltage
comparator. Its non inverting input (pin3)
receives half supply voltage through the
potential divider R2 and R3. Its inverting
input (pin2) gets a higher voltage only
when the sensor connected to points A
and B are shorted with moisture..

10. CONT’D….
 When the sensor is dry, the output of
IC1 will be high because its pin3 gets
more current than pin2. This high
output makes the transistor T1
conducting and Red LED lights. At the
same time T2 remains off because its
base is not getting current since T1
takes all the current. So Green LED
remains off.

11. CONT’D....
 When sensor gets moisture, current
flows through the sensor to the pin2 of
IC1.As a result, pin2 of IC1 gets more
current than pin3 and its out put
becomes low. T1 then turns off
allowing T2 to conduct. Red LED turns
off and Green LED turns on indicating
the presence of moisture.

12. WHAT CAN A MOISTURE SENSOR BE USED
FOR???
 Moisture sensors can be used in powdered
chemicals, to determine how-much and how-to feed
into processes. Moist powders can take extra drive
power, different types of feeding mechanisms, even
poison a process.
 Moisture sensors can be used to tell the relative
humidity, part of weather forecasting.

13. CONT’D….
 Moisture sensors can be used to control the humidity in a
greenhouse, by controlling a fan, say.
Moisture sensors can be used to assure the feedgas being sent
into an ozone generator is dry enough to make lots of ozone, and
very little nitric acid. You'd alarm and shut the generator down,
until the feedgas system was repaired.

14. REFERENCES
 http://electroskan.wordpress.com/2010/04/29/moisture-sensor
o http://www.gadgetronicx.com/2013/08/working-of-operational-amplifier-ic-
741.html
 http://www.engineersgarage.com/electronic-components/transistor-bc547-
datasheet