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2. HI Capacity http://hicapacity.org October 11th, 2011 Jeremy Chan
Arduino Night IV
HI Capacity
October 11th, 2011
Jeremy Chan

3. Tonight Temperature Sensors Reading Sensors Intro to Processing
Sensor Visualization
Tonight
What will we do?
Arduino (C/C++)
rocessing (Java)
RS232/USB
(Async Serial)

4. 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)

5. 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)

6. 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 2.2kΩ to 25C
Pros/Cons: Cheap / Non-Linear (Variable Sensitivity)
Products Available for -80°C to 150°C (-110°F to 302°F)
Non-Linear Temperature/Resistance Curves
Omega Thermistor Products
More Info:

7. Thermistor Temperature[C] vs R[Ω]
Datasheet / Calibration Constants: a,b,c,d,…
Example: Vishay 10k NTC Thermistor Assembly Curve
0C to 100C
27.35kΩ to 0.974kΩ
Temperature [°C]
R[kΩ]
Vishay Calculator:
Vishay Thermistor:

8. 2. Resistive Temperature Detectors
Precision PTC Resistors Made of Platinum
PTC: Positive Temperature Coefficient, R rises as T rises
Typical Values from 100Ω 25C
Pros/Cons: Accurate, Linear / Expensive, Low Level Signals
Products Available for -200°C to 500°C (-328°F to 932°F)
Near Linear Temperature/Resistance Curves
~ Ω/°C (3 Standard Classes for Different Temp Ranges Available)
US Sensor RTD Products
More Info:

9. RTD Temperature[C] vs R[Ω]
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[Ω]
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[Ω]

10. 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 -40°C to 125°C (-40°F to 257°F)
Texas Instruments TMP006
More Info:

11. 4. Thermocouples (TC) Any two dissimilar joined metals form TC’s
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 -200°C to 1800°C (-328°F to 3272°F)
Non-Linear Temperature/Resistance Curves
Up to 10 curve correction terms necessary for extremes
Omega Thermistor Products
More Info:

12. Approximate Type E TC Voltage Outputs
Hot Gradient
No Gradient
Cold Gradient -

13. Type E TC Voltage vs ΔTemperature
+/- 1.1C Approx, 0-94C
+/- 20.5C Approx
0-1024C

14. Ice Bath Cold Junction Compensation
Provides absolute temperature measurement vs 0C
Impractical for many applications to have an ice bath

15. 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:

16. Integrated Thermocouple Interface
Adafruit Breakout Board for MAX6675 Type K Thermocouple
Range: 0 to 1024C, Resolution: 0.25°C
SPI Serial Interface
Many other ‘simple’ thermocouple interface products available
More Info:
Example Code:

17. 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 -55°C to 150°C (-67°F to 302°F)
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

18. Tonight’s Sensors MCP9701A TC1047A
Output: 0.4V mV/C Range: -40C to 125C Accuracy: +/- 2C (0-70C) Supply: 6uA
Output: 0.4V mV/C Range: -40C to 125C Accuracy: +/- 0.5C (0-70C) Supply: 60uA

19. ADC High Level Concept Analog Domain ADC Digital Domain Input Voltage
Compare
Output Count
Software
Vin = count*(5/1023)
Vin = 2.498V

20. 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? 2^10 = 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 ~= V/count

21. 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

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

23. Step 1: Sensor Wiring MCP9701A TC1047A Red = 5V Red = 5V Blue = GND
White = Vout -> Analog A0
Red = 5V
Black = GND
Blue = Vout -> Analog A0

24. Step 2 Code Reading 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);
// Print Line via Serial Port
Serial.println(analogValue);
Initialize Variables
and Peripherals
Main Loop

25. Step 3 Code Calculating Voltage and Temperature
void loop() {
// Read Analog Channel 0
int analogValue = analogRead(0);
// Calculating Voltage, VREF=5V,0V;
float voltage = analogValue * 5 / ;
// Calculating Degrees C = (Volts-0.400) / 19.5mV
float deg_C = (voltage ) / ;
// 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 (" ");
Serial.print (voltage);
Serial.print (deg_C);
Serial.print (deg_F);
Serial.print (" "); // Extra space for easy parsing
Serial.print ("\n"); // Send Line Feed (New Line)
// Delay 66ms, slowing to rate of about 15Hz updates
delay(66); }
Main Loop Modification
MCP9701A Only
For TC1047, use:
(voltage-0.5)/0.01;

26. Processing Visualizations
“Just Landed” 3D Visualization of Twittering Travelers

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

28. 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

29. Questions about the Arduino?

30. Special thanks to Ian Kitajima and Oceanit!

31. Backup Slides

32. Measuring Resistive Sensors
Resistance of Thermistors & RTD’s
Ohm’s Law! V=IR -> R=V/I (Resistance = Voltage / Current)
Provide V or I excitation to find resistance ? ?

33. Measuring Resistive Sensors
Method 1: Excite with current, measure voltage
Difficulty: Precision low-current source required
Limited IC’s available (100uA, 200uA are common)
Not simple to build precision low-current sources
Question: Why not a high current source? ?

34. 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 ? ? ?

35. 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. 25C) ? ? ?

36. 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