National Electronics Museum Temperature Sensing Temperature Bar Graph

National Electronics Museum Temperature Sensing Temperature Bar Graph Project National Electronics Museum November 12, 2011

Temperature Bar Graph Project What you can expect in this segment National Electronics Museum We’ll Explain q q q What the project it is What its parts are How they work How they go together Your Project Board Soldering Temp Bar Graph rev- p. 2

Thermistor Temperature Bar Graph National Electronics Museum q What is it? An display of bars that indicate temperature at a probe q What are its main parts? Bar Graph Display Temperature probe Voltage Divider How does it work? . . . Temp Bar Graph rev- p. 3

Voltage Divider National Electronics Museum Series resistors across a voltage make a Voltage Divider § Voltage divides in proportion to the resistance values R 1=6 ohms 10 Volts 5 V 5. 0 V R 2=6 ohms 6 Ohms/ 12 Ohms X 10 V = 5 V R 2 / (total) 5 V R 1=4 ohms 10 Volts Resistor 6 Ohms/ 10 Ohms X 10 V = 6 V R 2 / (total) 4 V 6. 0 V R 2=6 ohms 6 V Temp Bar Graph rev- p. 4

Thermistor National Electronics Museum q Thermistor § A resistor that changes its value with temperature q 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. 5

Thermistor Temperature Measurement Voltage changes with temperature in this divider National Electronics Museum q Use a Thermistor as a resistor in a Voltage Divider q Then voltage out of divider will vary with temperature Thermistor resistance varies with temperature R 1=Variable 10 Volts Variable So voltage out of divider varies with temperature R 2=Fixed Temp Bar Graph rev- p. 6

Displays come in different “flavors” National Electronics Museum Analog Meters – needle and scales q Digital Meters – alpha-numeric q Graphic Displays – images, colors, patterns q We’ll use a Bar Graph with Light Emitting Diodes (LEDs). . . Temp Bar Graph rev- p. 7

LED BAR GRAPH LED Bar Graphs turn voltage into lighted bars National Electronics Museum Number of Lighted LED varies with voltage input q More voltage lights more LED bars q Voltage In LED BARGRAPH and Driver Temp Bar Graph rev- p. 8

Temp Sensor with Bargraph Readout Rising bars indicate rising thermistor temperature National Electronics Museum Combine Voltage Divider with Driver & Bar Graph § Thermistor probe changes the voltage divider § LED Driver & Display changes the voltage into bars Thermistor 9 V Battery Temp R 1=Variable Voltage In LED BARGRAPH and Driver Bars R 2=Fixed Temp Bar Graph rev- p. 9

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

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

Parts Layout National Electronics Museum U 2 Bargraph Chamfered Corner to Upper Right Battery Clip Red + U 1 Driver “Dimple” To Left Capacitor C 1 Black Stripe Thermistor RT Diode D 1 Band = Cathode Resistor R 4, 2. 2 K Red-Red_Red Resistor R 2, 150 K Brn_Grn-Yel Adjust so one or two bars are lighted. Then heat with fingers, etc. Have fun! Resistor R 3, 240 K Red-Yel Resistor R 5, 5 K Potentiometer Temp Bar Graph rev- p. 12

A Word about Soldering Electronic parts are connected using solder National Electronics Museum Solder bonds metal together § Usually copper wire and copper Pads or terminals q Metal must be hot enough to melt solder to make it “stick” q Always heat the metals and let them melt the solder § Simply melting the solder alone makes a poor “cold joint” q 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. Temp Bar Graph rev- p. 13