Temperature Sensing Temperature Bar Graph Project National Electronics Museum November 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 National Electronics Museum 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 National Electronics Museum Voltage Divider Series resistors across a voltage make a Voltage Divider  Voltage divides in proportion to the resistance values 5.0 V 10 Volts 5V R1=6 ohms R2=6 ohms 6.0 V 10 Volts 4V 6V R1=4 ohms R2=6 ohms 6 Ohms/ 12 Ohms X 10V = 5V R2 / (total) 6 Ohms/ 10 Ohms X 10V = 6V R2 / (total) Resistor

Temp Bar Graph rev- p.5 National Electronics Museum 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 National Electronics Museum Thermistor Temperature Measurement  Use a Thermistor as a resistor in a Voltage Divider  Then voltage out of divider will vary with temperature Variable 10 Volts R1=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 National Electronics Museum 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 National Electronics Museum LED BAR GRAPH  Number of Lighted LED varies with voltage input  More voltage lights more LED bars Voltage In LED BARGRAPH and Driver LED Bar Graphs turn voltage into lighted bars

Temp Bar Graph rev- p.9 National Electronics Museum 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 In LED BARGRAPH and Driver 9V Battery 9V Battery R1=Variable R2=Fixed Thermistor Temp Bars

Temp Bar Graph rev- p.10 National Electronics Museum Divider Voltage Temp Sensor with Bargraph Readout Divider Display Schematic diagram shows all the parts

Temp Bar Graph rev- p.11 National Electronics Museum Completed Project Board What YOU will build!

Temp Bar Graph rev- p.12 National Electronics Museum Parts Layout Capacitor C1 Black Stripe - Battery Clip Red + Diode D1 Band = Cathode Resistor R2, 150K Brn_Grn-Yel Thermistor RT Resistor R4, 2.2K Red-Red_Red Resistor R3, 240K Red-Yel-Yel Resistor R5, 5K Potentiometer U2 Bargraph Chamfered Corner to Upper Right U1 Driver “Dimple” To Left Adjust so one or two bars are lighted. Then heat with fingers, etc. Have fun!

Temp Bar Graph rev- p.13 National Electronics Museum  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