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Before we get started...

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Arduino Night IV

• HI Capacityhttp//hicapacity.org
• October 11th, 2011
• Jeremy Chan

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Tonight

• Temperature Sensors
• Reading Sensors
• Intro to Processing
• Sensor Visualization

• What will we do?

Arduino (C/C)
rocessing (Java)
RS232/USB
(Async Serial)
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Temperature Sensor Applications

• Cooking (Hot Plate and Oven Control)
• Soldering (Soldering Irons, Reflow Ovens)
• Thermal Management (Servers, HVAC)
• Environmental Monitoring
• Thermal Safety (Motors, Boilers, Batteries)
• Food Safety (Refrigeration/Freezing)
• Characterization (Thermal Conductivity)

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Temperature Sensors

• Overview on
• Thermistors
• Resistive Temperature Detectors (RTD)
• 3. Non-Contact IR Sensor (TI TMP006)
• 4. Thermocouples (Wide Range)
• 5. Semiconductor Band-Gap (Easy Interface)

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1. Thermistors

• Resistors Made of NTC or PTC materials
• NTC Negative Temperature Coefficient, R falls as
  T rises
• PTC Positive Temperature Coefficient, R rises
  as T rises
• Typical Values from 2.2k? to 100k? _at_ 25C
• Pros/Cons Cheap / Non-Linear (Variable
  Sensitivity)
• Products Available for -80C to 150C (-110F to
  302F)
• Non-Linear Temperature/Resistance Curves

Omega Thermistor Products
More Info http//www.omega.com/temperature/z/pdf
/z036-040.pdf
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Thermistor TemperatureC vs R?
Datasheet / Calibration Constants a,b,c,d,
Example Vishay 10k NTC Thermistor Assembly Curve
0C to 100C 27.35k? to 0.974k?
Temperature C
Rk?
Vishay Calculator http//www.vishay.com/doc?2911
3 Vishay Thermistor http//www.vishay.com/docs/29
092/ntcalug.pdf
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2. Resistive Temperature Detectors

• Precision PTC Resistors Made of Platinum
• PTC Positive Temperature Coefficient, R rises as
  T rises
• Typical Values from 100? -10k? _at_ 25C
• Pros/Cons Accurate, Linear / Expensive, Low
  Level Signals
• Products Available for -200C to 500C (-328F to
  932F)
• Near Linear Temperature/Resistance Curves
• 0.00385?/C (3 Standard Classes for Different
  Temp Ranges Available)

US Sensor RTD Products
More Info http//www.ussensor.com/prod_Probes_RT
Ds.html
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RTD TemperatureC vs R?

• All excitations induce some self-heating
• Less power Less self-heating Less error
  Less signal
• Excitation can be disabled, but be aware of
  fluctuations in temperature due to transient
  self-heating

Example Pt100 RTD
Temperature C
R?
Thermistor Steinhart-Hart Equation
- Datasheet / Calibration Constants a,b,c
Curve Fit Error C
RTD, R to Temperature
- Datasheet/Calibration Constants a,b,c
R?
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3. Non-Contact IR Temperature

• Infrared Thermopile Sensor TMP006
• Tiny chip-scale package IR sensor (1.6mm x 1.6mm)
• Pros extremely small, non-contact measurement,
  serial output
• Cons extremely small, IR emissivity cal. reqd.,
  requires well-laid PCB
• TMP006 Measures for -40C to 125C (-40F to
  257F)

Texas Instruments TMP006
More Info http//www.ti.com/product/tmp006
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4. Thermocouples (TC)

• Any two dissimilar joined metals form TCs
• Seebeck effect voltage developed over entire
  length of wire
• Several standard thermocouple types available
• Pros/Cons TRange / tiny signal (uV), relative
  temperature only
• Products Available for -200C to 1800C (-328F
  to 3272F)
• Non-Linear Temperature/Resistance Curves
• Up to 10 curve correction terms necessary for
  extremes

Omega Thermistor Products
More Info http//www.ti.com/lit/ml/slyp161/slyp16
1.pdf
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Approximate Type E TC Voltage Outputs
Hot Gradient
No Gradient
Cold Gradient
-
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Type E TC Voltage vs ?Temperature
/- 1.1C Approx, 0-94C
/- 20.5C Approx 0-1024C
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Ice Bath Cold Junction Compensation

• Provides absolute temperature measurement vs 0C
• Impractical for many applications to have an ice
  bath

http//en.wikipedia.org/wiki/Thermocouples
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Software Cold Junction Compensation
Remote Thermocouple
Analog to Digital Converter
Local Temp Sensor
Cold Jct T/V Known
1. Measure (TC Voltage) and (Cold Junction
Temperature) 2. Use (Cold Jct. Temperature) to
calculate (Compensation Voltage) - Use TC curve
to calculate cold junction voltage 3. Add
(Compensation Voltage) and (TC Voltage) 4. Use TC
Curve to calculate temperature at remote TC
junction
More Info http//www.maxim-ic.com/app-notes/index
.mvp/id/4026
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Integrated Thermocouple Interface
Adafruit Breakout Board for MAX6675 Type K
Thermocouple Range 0 to 1024C, Resolution
0.25C SPI Serial Interface Many other simple
thermocouple interface products available
More Info http//www.adafruit.com/products/269 Ex
ample Code http//www.ladyada.net/learn/sensors/t
hermocouple.html
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5. Semiconductor Band-Gap

• Band-Gap Reference Based Sensor
• Precision current forced through diode
• Diode forward voltage based on temperature
• Voltage measured, amplified
• Multiple output options Alarm Logic, Analog,
  Serial
• Pros/Cons Small, Cheap, Easy / T Range, Remote
  Fragility
• Products Available for -55C to 150C (-67F to
  302F)
• Linear Temperature Curves w/ Error Bounds

Example SOT-23-6
Microchip Tech. MCP9701A TO-92 Package
Microchip Tech. TC1047A SOT23 Package
Maxim Integrated Products MAX6626 SOT23-6 Package
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Tonights Sensors

• MCP9701A

• TC1047A

• Output 0.4V 19.5mV/C
• Range -40C to 125C
• Accuracy /- 2C (0-70C)
• Supply 3.1-5.5V _at_ 6uA

• Output 0.4V 10.0mV/C
• Range -40C to 125C
• Accuracy /- 0.5C (0-70C)
• Supply 2.3-5.5V _at_ 60uA

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ADC High Level Concept
Analog Domain
Digital Domain
ADC
Input Voltage
Compare
Output Count
Software Vin count(5/1023) Vin 2.498V
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How are we going to read the sensors?

• To read voltages, use an analog to digital
  converter!
• Converts voltage into a numerical count
• Arduino ADC
• 10 bits of counting (a.k.a. 10 bit
  resolution/quantization)
• How many levels? 210 1024
• Highest count? 1023, because 0 takes up one of
  them!
• Single-Ended (input is always referenced to
  Arduino GND)
• By default
• VREF 5V, VREF- 0V (single ended)
• VREF- is the voltage at the 0 count
• VREF is the voltage at the full-scale 1023 count
• All counts 0 and 1023 are essentially equal
  increments
• 1023 counts amongst 5V is 5/1023
  0.00488V/count

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Let The Hands-On Activities Begin!

• Arduino

• Processing

• Step 0 Installation / Orientation
• Step 1 Connecting MCP9701A
• Step 2 Reading Analog to Serial (Code)
• Step 3 Converting Analog to Voltage and
  Temperature (Code)
• If we have time
• Step 4 Extra Formatting Standard String (Code)

• Step 0 Installation / Orientation
• Step 1 Drawing Boxes
• Step 2 Serial Input and Events (String Example)
• Step 3 Parsing Serial Strings
• Step 4 Real-Time Bar Graph
• Step 5 Real-Time Chart
• Step 6 Logging CSV Files
• If we have time
• Step 7 Extra User Input, Events, and Screenshots
• Step 8 Extra Exporting Applications

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Arduino Orientation

• 1. Software Installation
• 2. Essential Hardware Features for Tonight
• 3. Examples Library Run-Thru
• 4. Disconnect Arduino for Wiring Step

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Step 1 Sensor Wiring

• MCP9701A

• TC1047A

Red 5V Blue GND White Vout -gt Analog A0
Red 5V Black GND Blue Vout -gt Analog A0
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Step 2 CodeReading the Analog to Digital
Converter

• void setup()
• // Setup Serial Port, 9600bps
• // Implied 8-N-1 8 Bit Transfers, No Parity,
  1 Stop Bit
• Serial.begin(9600)
• void loop()
• // Read Analog Channel 0
• int analogValue analogRead(0)

Initialize Variables and Peripherals
Main Loop
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Step 3 CodeCalculating Voltage and Temperature

• void loop()
• // Read Analog Channel 0
• int analogValue analogRead(0)
• // Calculating Voltage, VREF5V,0V
• float voltage analogValue 5 / 1023.0
• // Calculating Degrees C (Volts-0.400) /
  19.5mV
• float deg_C (voltage - 0.400) / 0.0195
• // Calculating Fahrenheit 9/5 C 32
• // Note A common mistake is to use 9/5. 9/5
  1 (Integer Math)
• // Use 9.0/5.0 to ensure floating point
  math ( 1.8)
• float deg_F (9.0/5.0)deg_C 32
• // Print out voltage, degrees C, and degrees F
  
• Serial.print(analogValue)
• Serial.print (" ")

Main Loop Modification
MCP9701A Only For TC1047, use (voltage-0.5)/0.01

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Processing Visualizations
Just Landed 3D Visualization of Twittering
Travelers
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Processing Orientation

• 1. Software Installation
• 2. Examples Library Run-Thru
• 3. Arduino Night IV Code!

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Processing Code

• Step 1 Drawing Boxes
• Step 2 Serial Input and Events (String Example)
• Step 3 Parsing Serial Strings
• Step 4 Real-Time Bar Graph
• Step 5 Real-Time Chart
• Step 6 Logging CSV Files

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Questions about the Arduino?

•  

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Special thanks to Ian Kitajima and Oceanit!
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Backup Slides
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Measuring Resistive Sensors

• Resistance of Thermistors RTDs
• Ohms Law! VIR -gt RV/I (Resistance
  Voltage / Current)
• Provide V or I excitation to find resistance

?
?
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Measuring Resistive Sensors

• Method 1 Excite with current, measure voltage
• Difficulty Precision low-current source required
  
• Limited ICs available (100uA, 200uA are common)
• Not simple to build precision low-current sources
• Question Why not a high current source?

?
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Measuring Resistive Sensors

• Method 2 Excite with voltage, measure current
• Difficulty Precision measurements of current
  required
• Precision Current Sense Resistor (Rs) Required
• Low Temperature Coefficient Ideal
• Smaller current sense resistors are better for
  linearity

?
?
?
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Measuring Resistive Sensors

• Method 3 Excite with significant voltage divider
• Difficulty Measurements of R are very non-linear
• Precision Voltage Divider Resistor Required
• Allows biasing of nominal temperature voltage
  (e.g. 2.5V _at_ 25C)

?
?
?
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Measuring Resistive Sensors

• All excitations induce some self-heating
• Trade between error and magnitude of signal
• Low enough excitations induce no noticeable error
• Excitation can be pulsed on/off to minimize
  self-heating
• Leads to transient increase in temp, so keep
  pulses short
• Much less predictable offsets than constant
  excitation
• Current running through remote measurement leads
  can drop voltage, resulting in measurement errors
• Look for 3 wire and 4 wire configurations for
  more accuracy
• Look-up tables can be used to speed up
  calculations
• Linear approximations between points on an
  exponential curve
• Trade between accuracy and computation time