project report: frost alert led display - 2010 july

Anyone who wish to borrow ideas, or schematics may do so with proper reference. ~ Hussain Ageel Naseer ~

Project Report: Frost Alert LED Display

Diploma in Telecommunication and Computer Engineering

Name: Hussain Ageel Naseer

Student #: 51375

Country: Rep. of Maldives

Lecturer: Chan Yun Ghit

Date: 25th June 2010


Content Page

Abstract…………………………………………………………………………….. 3

Acknowledgement………………………………………………………………….. 4

Chapter 1

1.1 Introducation…………………………………………………………… 5

1.2 Objectives of the project……………………………………………….. 6

1.3 List of diagrams………………………………………………………... 6

Chapter 2

2.1 Literature review……………………………………………………….7

2.2 Components and its functions………………………………………….9

Chapter 3

3.1 Methodology…………………………………………………………... 12

3.2 Block diagrams of the Frost Alert Circuit……………………………...15

3.3 Final block diagram of Frost Alert Circuit……………………………..16

3.4 Schematic diagrams…………………………………………………….17

3.5 Combined Circuits………………………………………………………19

Chapter 4

4.1 Results and discussion…………………………………………………..20

Chapter 5

5.1 Conclusion……………………………………………………………….21

5.2 Future development……………………………………………………...22

Chapter 6

6.1 Gantt chart……………………………………………………………….23

6.2 Component Prices……………………………………………………….24

Chapter 7

7.1 Reference…………………………………………………………………25


Abstract

This project, Frost Alert Display, switches on an LED display circuit, keeps the LED display

flashing, when the temperature sensor detects that the temperature has reached freezing point.

This circuit consists of three building blocks. First building block uses an Integrated circuit (IC)

amplifier which responds to change in temperature. This turns on an astable based on a 555

timer. The output of the 555 timer inputs an IC 4017, which runs LED display.


Acknowledgment

In order to finish my project, I have had a lot of help from my fellow class mates. Out

of them, I would like to give special thanks to:

Ahmed Sako

Hsuing Khee

Diresh Kumar

Ashraf Abubakur

Lim Chee Bing

I’ve gained a lot of important information on the projects, and ideas for my project

from them. Also I have got help from them to troubleshoot my circuit.

In addition to them, I would like to thank my supervisor Ms. Chan Yun Ghit. She was

always available most of the time if I had any question regarding my project. And also

her explanations have made me understand more about the circuit. Her being available

most of the time made it very convenient for me to get to her and solve the problems I

had.

I thank all those who helped me with my project.


CHAPTER 1

1.1 Introduction

The Frost Alert Display is used to figure out when the temperature of the environment,

it is in, is at 0˚. The idea of developing this circuit is to be able to take precautions as

soon as you can, so that you can be protected from the cold weather. This can also be

used to make sure if the temperature of the freezer or storage is at 0˚C.

The Frost Alert Display uses a thermistor to detect the temperature surrounded and

alert when it reaches 0˚C by turning on an LED display. Thermistors are resistors

which varies its resistivity as the temperature changes. There are several types of

thermistors and are used for various purposes. Some of its purpose includes: meter

compensation, inrush-current device, and LED control.

LED displays are made up of LEDs. LED, in other words Light Emitting Diodes emits

light when current is passed through it. LED displays are very common. It can be used

to display words, as well as any character. 7-segment LED display is used to display

numbers while dot matrix LED display is used to display letters and numbers.


1.2 Objectives of the Project

Understanding how to turn on an LED display when a thermistor gives out the

resistance equivalent to 0˚C is one of the main objectives of the project. Another

objective was to understand how to make the LEDs display flash when the thermistor’s

detects frost temperature (0˚C).

The main aim of this project is to use all I’ve learned from the past two years to gather

information about the projects: this includes circuit diagrams, and information on the

components. Also the project looks at how well you can edit, and troubleshoot a

circuit.

1.3 List of Diagrams

Temperature Sensor with Operational Amplifier.

IC 555 timer

Frost Alert Circuit

Final Circuit (The three circuits above combined to make a single circuit)

LED Display (Display’s the word ICE)

16-LED running lights


Chapter 2

2.1 Literature Review

A temperature sensor usually works along with another component which monitors the

change of temperature. In today’s World there are different types of sensors and are

being used in different ways in order to create temperature reading circuits. Even

though there are several types of temperature sensors, they all follow one common

thing: all these sensors measures the temperature by sensing the change in physical

characteristics.

The most common seven basic types of temperature sensors includes thermocouples,

resistive temperature devices (RTDs, Thermistors), infrared radiators, bimetallic

devices, liquid expansion devices, molecular change-of-state, and silicon diodes. Each

of these temperature sensors has their own ability in order to measure the temperature.

Thermocouples vary the voltage passing through it with the change in temperature, but

the RTDs vary its resistance (the amount of current passing through it) with the change

in temperature. On the other hand, infrared sensors use infrared radiation to detect the

temperature. Bimetallic sensors and liquid expansion devices have the ability to expand

when it is heated, so the temperature is measured my monitoring the expansion in the

sensor. In molecular change-of-state sensors, the temperature is being recorded when

the material changes its state.


Frost Alert Circuit

This project turns on an LED display when the temperature sensor, a thermistor, senses

the air temperature surrounded it has fallen to 0˚C (meting / freezing point). This

circuit is made up of two building blocks.

Fig.1: Frost Alert Circuit

The first block is an Operating Amplifier, an integrated circuit (IC), which works as a

switch that triggers a 555 timer (IC). The Operational Amplifier in the circuit acts as a

comparator which compares two signals and triggers the output when it detects a better

signal. The Variable resistor is used to set the Op Amp so that when it detects a

specific resistance. The IC 555 timer is used as an astable which keeps on switching

ON and OFF allowing an unstable signal passing through it.


2.2 Components and its function.

Thermistor

A thermistor is a sensor which is used to measure the temperature. Thermistors are

resistors which are sensitive to temperature and vary as the temperature changes. Even

though most of the resistors increase its resistivity with the increase in temperature,

thermistors decrease its resistance as the temperature rises. However, thermistors are

used for simple temperature measurements, because it can only have reasonable output

voltage.


Integrated Circuits (IC):

Integrated circuits are complex circuits which is been fixed in to a tiny chip, and is

made of semiconductor materials.

IC 3140 is an integrated circuit operational amplifier that combines the high voltage

PMOS transistor with the high voltage bipolar transistor on a single chip. This chip has

a high input Impedance, and a very low input current, and performs at a very high

speed. This IC is used widely in different application. Some of the application includes:

sample and hold amplifier, Peak Detector, Active Filter, Comparators, and in

photocurrent instrumentation.

Top view of IC 3140

IC 555 timer can be used in astable and/or monostable mode, depending on the type of

curciut. In astable mode this IC creates continuous series of pulses. Unlike astable, in

monostable mode this IC outputs a single pulse. IC 555 timer can be used as the source

or the sink, and wide range devices are can be used with it.

Top view of a 555 timer


Resistors:

Resistors are components which are used to control the current flowing through a

circuit. To achieve this, it drops the voltage between two points. Resistors completely

reply on the Ohm’s law: which is, V=IR.

There are two basic types of resistors. Those are Fixed-value resistors and variable

resistors. The resistance of fix-value resistors remains the same, while the resistance of

variable resistor can be changed between its resistance range.

Fixed value resistor Variable resistor

Capacitor

Capacitors are used to store electric charge. It is used to smooth the DC voltage passing

through it. In addition they are used in filter circuits as current flows through it as long

as an AC voltage source is connected to it.

Capacitors


Light Emitting Diodes (LED)

Light Emitting Diodes (LEDs) are diodes made of semiconductors, which allows

current to follow only in one direction (forward bias). In LED, two slightly different

materials are kept close together to form a PN junction. LED requires low power, and

has a high efficiency and has a longer life span. Also LEDs can be dimmed and

switched rapidly causing no problems to them, unlike an ordinary bulb.

Some of the applications of the LEDs are Illumination, status indicators, automotive

industries, outdoor lighting and signage.


Chapter 3

3.1 Methodology

Circuit Explanation:

The frost alert circuit uses an integrated circuit (IC 3140) as a comparator, and

compares two currents and switches its output indicating which input signal is stronger.

When the V+ (pin 3) of the op amp detects a higher current than V- (pin 2) the output

signal is high. When V+ detects a signal lower than the signal in V- the output signal is

low.

The temperature sensor used in the frost alert circuit is a resistive temperature device, a

thermistor. It varies the resistance with the change in temperature of its surrounding.

So, in order to measure the temperature using thermistor, a thermistor is connected to

the pin-3 (V+) of integrated circuit operational amplifier, IC 3140, with a variable

resistor connected in series. The variable resistor is used to set the current value

passing through the V+. The pin-2 (V-) is connected to a series of fixed resistors. With

this setup, the pin-3 can vary its resistance. This will output a positive pulse at the pin6.

Figure 2: Integrated Circuit Operational Amplifier


The output signal from the IC Op Amp is then connected to the pin-4 (reset) of another

integrated circuit (IC 555 timer). In the frost alert circuit, it uses a 555 timer in astable

mode. In the astable mode the timer creates a series of pulse in the output. Once the IC

555 timer gets an input signal in the pin-4 (reset) it sends a series of pulse through the

pin-3 (output). An LED is connected to the output and is grounded. The IC 555 timer is

used as a source in the frost alert circuit.

Figure 3: Astable mode based 555 Timer


3.2 Block Diagrams of the Frost Alert Circuit

Input

Figure 4: The block diagram of Frost Alert Circuit

There are three main types of components used in this circuit. A temperature sensor,

integrated circuits, and LED display. IC 3140 acts as a comparator and detects the

change in signal strength from the thermistor, and sends a pulse to the 555 timer. The

555 timer then outputs a series of pulse on its output.

IC 3140

Thermistor

555 Timer

Output


3.3 Final Block Diagram of Frost Alert Display Circuit

Figure 5: Block diagram of frost alert LED display circuit

In the final block diagram, there are two additional blocks: IC 4017 and an LED

display. The output from the 555 timer is connected to IC 4017’s input. The output

signals from IC 4017 is used to run the LED display.

IC 3140

Thermistor

555 Timer

LED Display

IC 4017


3.4 Schematic Diagrams

Schematic Diagram of LED Display

Figure 6: LED Display (LEDs are connected to write ICE)

I have connected all the LEDs, so that when a voltage is passed through, it turns on the

LEDs. All these LEDs are connected to print the word “ICE”. The resistor in the circuit

limits the amount of current passing through the circuit.


Schematic Diagram of a different circuit using IC 4017

Figure 7: 16-LED running lights

At first I finished the frost alert circuit using two ICs. The circuit works perfectly,

turning the LED display ON when the temperature sensor senses freezing temperature.

But the all the LEDs were turned ON or OFF with respect to the comparator. I wanted

LED display to be flashing when the sensor detects the freezing point.

For that reason I searched and found the “16-LED running lights” circuit (figure 7). At

first I tried to input the signal from the 555 timer IC 4017’s input without bringing any

change to the circuit. But for some reasons the LEDs didn’t turn ON.

After reading the datasheet for IC 4017, I took off all the components on the left side of

the schematic diagram, and connected the 555 timer to its CP0 of the IC 4701. As the

555 timer used is astable mode based, the timer keeps on sending a series of pulse

when the temperature sensor detects freezing point. This makes turns the CP0 from

LOW to HIGH, as a result display flashing rapidly.


3.5 Combined Circuits

Figure 8: the final circuit

This diagram shows the three ICs combined together to form a single circuit. In this

circuit, the Op Amp acts as a comparator and detects the change in temperature and

sends an output signal. As the Op Amp is connected to the 555 timer’s reset pin, it

resets the 555 timer resulting in a series of pulse moving out of the 555 timer. The 555

timer output is connected to the CP0 (low to high) leg of the IC 4017. This turn the

LED Display ON and keeps flashing.


Chapter 4

4.1 Results and Discussion

While working on the circuit, the resistance of the thermistor has been noted at three

different temperatures. The graph below shows the relationship between the resistance

of the thermistor and the temperature around it.

Figure 9: a bar chart showing the relationship between temperature and resistance in a thermistor

According to data I have recorded, the resistance of the thermistor increase with the

decrease in temperature, and with the increase in temperature the resistance decreases.

This answers the question, how does a thermistor detect the change is temperature.

That is, when the temperature detects that the resistivity of it is going down, it

considers that the outside temperature is rising. Vise verse when the resistivity goes up.

0

2

4

6

8

10

12

14

16

18

Room Temp. Body Temp. Frost

temp. vs resistance

Series 1


Chapter 5

5.1 Conclusion

Throughout the project, I’ve learned several things about electronic components. I’ve

learned about the different types of fix-resistors and variable resistors. Specially on

integrated circuits, as well as on different types of thermistors. I’ve gained a lot of

knowledge on how the Operational Amplifiers work, and how it can be used as a

comparator. Also I’ve gotten a lot of experiences while working on the projects which

would probably help me in my future.


5.2 Future development

While doing the project, I figured out that this circuit can be used to detect any

temperature within the range of the thermistor used. So I believe this same circuit can

be used not only for frost alert, but also for any other lower temperature.

With a little change of circuit, it can be made to turn on a siren to alert people. I think

this could be a better way to get people’s concentration.

This circuit can also be used as a overheat detector. For an example, this can be used to

detect the car engine temperature


Chapter 6

6.1 Gantt chart:


6.2 Component Prices

Components quantity Prices (RM)

Thermistor (4.7kΩ at 25˚C) 1 1

IC 3140 1 5

IC 555 timer 1 6.5

Resistors 10kΩ, 10kΩ, 1MΩ. 47kΩ, 47kΩ 5 0.50

Variable resistor (22kΩ) 1 0.70

Capacitor ( 0.5µF, 100µF) 2 0.20

IC 4017 1 6

9v Battery 1 5

LEDs (red colour) 25 2.50

Total 27.40


Chapter 7

7.1 Reference:

http://www.wwdmag.com/The-Seven-Basic-Types-of-Temperature-Sensors-article658

http://www.temperatures.com/sensors.html

http://www.facstaff.bucknell.edu/mastascu/eLessonsHTML/Sensors/TempR.html

http://www.ehow.com/about_5039188_uses-thermistor.html


http://www.kpsec.freeuk.com/components/ic.htm

http://www.intersil.com/data/fn/fn957.pdf

http://www.doctronics.co.uk/555.htm

http://www.wisegeek.com/what-are-resistors.htm

http://www.lrc.rpi.edu/programs/nlpip/lightinganswers/led/whatIsAnLED.asp

http://www.bodine.com/products/whatsled.html

http://www.facstaff.bucknell.edu/mastascu/elessonshtml/Interfaces/ConvComp.html

Books:

Teach Yourself: Electronics Malcolm Plant

http://www.wwdmag.com/The-Seven-Basic-Types-of-Temperature-Sensors-article658

http://www.temperatures.com/sensors.html


http://www.ehow.com/about_5039188_uses-thermistor.html


http://www.kpsec.freeuk.com/components/ic.htm

http://www.intersil.com/data/fn/fn957.pdf

http://www.doctronics.co.uk/555.htm

http://www.wisegeek.com/what-are-resistors.htm

http://www.lrc.rpi.edu/programs/nlpip/lightinganswers/led/whatIsAnLED.asp

http://www.bodine.com/products/whatsled.html

http://www.facstaff.bucknell.edu/mastascu/elessonshtml/Interfaces/ConvComp.html

project report: frost alert led display - 2010 july

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