Temperature Sensing Temperature Bar Graph Project

National Electronics MuseumNovember 12, 2011

National Electronics Museum

Temp Bar Graph rev- p.2

National Electronics Museum

Temperature Bar Graph Project

What the project it is What its parts are How they work How they go together Your Project Board Soldering

We’ll Explain

What you can expect in this segment

Temp Bar Graph rev- p.3

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Thermistor Temperature Bar Graph

What is it?An display of bars that indicate temperature at a probe

What are its main parts?

How does it work? . . .

Temperature probe

Bar Graph Display

Voltage Divider

Temp Bar Graph rev- p.4

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Voltage Divider

Series resistors across a voltage make a Voltage Divider Voltage divides in proportion to the resistance values

5.0 V10 Volts5V

5V

R1=6 ohms

R2=6 ohms

6.0 V10 Volts4V

6V

R1=4 ohms

R2=6 ohms

6 Ohms/ 12 Ohms X 10V = 5VR2 / (total)

6 Ohms/ 10 Ohms X 10V = 6VR2 / (total)

Resistor

Temp Bar Graph rev- p.5

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Thermistor

Thermistor A resistor that changes its value with temperature

Thermistor Temperature Coefficient (TC) TC describes how the resistance changes with

temperature Negative Temp Coefficient (“NTC”)

– Resistance decreases with increasing temperature

– Temp gets higher - Resistance becomes lower– Temp gets Lower – Resistance becomes higher

Let’s use this feature in a Voltage Divider . . .

Temp Bar Graph rev- p.6

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Thermistor Temperature Measurement

Use a Thermistor as a resistor in a Voltage Divider

Then voltage out of divider will vary with temperature

Variable10 VoltsR1=Variable

R2=Fixed

Thermistor resistance varies with temperature

So voltage out of divider varies with temperature

Voltage changes with temperature in this divider

Temp Bar Graph rev- p.7

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Displays

Analog Meters – needle and scales Digital Meters – alpha-numeric Graphic Displays – images, colors, patterns

We’ll use a Bar Graph with Light Emitting Diodes (LEDs) . . .

Displays come in different “flavors”

Temp Bar Graph rev- p.8

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LED BAR GRAPH

Number of Lighted LED varies with voltage input

More voltage lights more LED bars

Voltage InLED

BARGRAPH and Driver

LED Bar Graphs turn voltage into lighted bars

Temp Bar Graph rev- p.9

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Temp Sensor with Bargraph Readout

Combine Voltage Divider with Driver & Bar Graph Thermistor probe changes the voltage divider LED Driver & Display changes the voltage into bars

Rising bars indicate rising thermistor temperature

Voltage InVoltage InLED

BARGRAPH and Driver

9VBattery

9VBattery

R1=Variable

R2=Fixed

ThermistorTemp

Bars

Temp Bar Graph rev- p.10

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Divider Voltage

Temp Sensor with Bargraph Readout

Divider

Display

Schematic diagram shows all the parts

Temp Bar Graph rev- p.11

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Completed Project BoardWhat YOU will build!

Temp Bar Graph rev- p.12

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Parts Layout

Capacitor C1Black Stripe -

Battery ClipRed +

Diode D1Band = Cathode

Resistor R2, 150KBrn_Grn-Yel

Thermistor RT

Resistor R4, 2.2KRed-Red_Red

Resistor R3, 240KRed-Yel-Yel

Resistor R5, 5KPotentiometer

U2 Bargraph Chamfered Cornerto Upper Right

U1 Driver“Dimple” To Left

Adjust so one or two bars are lighted.Adjust so one or two bars are lighted.Then heat with fingers, etc. Have fun!Then heat with fingers, etc. Have fun!

Temp Bar Graph rev- p.13

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Solder bonds metal together Usually copper wire and copper Pads or terminals

Metal must be hot enough to melt solder to make it “stick”

Always heat the metals and let them melt the solder Simply melting the solder alone makes a poor “cold joint”

A Word about Soldering

Soldering temperatures are over 700 degrees F! Be Careful Only touch the soldering iron insulated handle Never set the iron down anywhere but in its

holder Wires will get hot. Hold them with a tool or not at

all.

Electronic parts are connected using solder