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Gadget Lab Lecture 5: Sensors and Interfacing… Components… More Project Time

Gadget Lab Lecture 5: Sensors and Interfacing… Components… More Project Time. Dr. Cindy Harnett ECE Dept., U of Louisville Spring 2008. Sensor projects are abundant. Especially low power wireless sensors. Example of a wireless sensor computer interface (Crossbow).

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Gadget Lab Lecture 5: Sensors and Interfacing… Components… More Project Time

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  1. Gadget Lab Lecture 5:Sensors and Interfacing…Components…More Project Time Dr. Cindy Harnett ECE Dept., U of Louisville Spring 2008

  2. Sensor projects are abundant Especially low power wireless sensors Example of a wireless sensor computer interface (Crossbow) Example of wireless sensor deployment: UMASS BOSTON Center for Coastal Environmental Sensing Networks

  3. Need to get an electrical signal from a sensor • Most common: Resistive sensors. Measurement -> Resistance Change ->Voltage change. Pressure, sound, temperature, acceleration • Capacitive sensors: touchpad, touchscreen. Typically look for a shift in resonant frequency in a “LC resonator” circuit to determine C. • Inductive sensors: A coil experiences a changing magnetic flux and captures some of the energy as an induced current. Encompasses RFID, antennas and even magnetic resonance imaging (MRI). • Optical sensors: remote control receiver, optical mouse. Detect the current when light interacts with electrons in a photosensitive material • More exotic types: high energy particle detectors, field-effect sensors, quantum sensors, scanning tunneling microscope.

  4. We have an electrical signal, now what? Record the electrical signal on a computer Or react to the signal in “real time” (Segway or car airbag for example). Usually must apply “signal conditioning” to the raw signal: Amplify a current from nA to mA, or voltage from mV to V Measure the frequency of a periodic signal Digitizean analog signal Debounce a flickering signal such as a button press And similar operations

  5. For common signal conditioning problems, your work is done. Gain = (1+ RB/RA). “Operational Amplifier” multiplies a voltage. Typically ~10x depending on configuration Some instrumentation amplifier ICs turn current to a proportional voltage. A “comparator” sends out a digital pulse when one voltage passes another. “Frequency counters” and analog-to-digital converters are usually a combination of a timer, a comparator and a computer memory (more) Debouncer: the “Schmitt Trigger” is like a comparator with two different thresholds (more)

  6. The Schmitt Trigger • Available as an IC similar to the inverter in the Firefly project • There’s an “up” threshold that’s higher than the “down” threshold http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/schmitt.html • This prevents the circuit from switching rapidly on and off when the input voltage is near a threshold

  7. The analog-to-digital converter Cheaper alternative: compare the analog voltage with a ramped voltage, and count the number of milliseconds until the ramped voltage surpasses the analog voltage. The millisecond count is a “digital” representation. • Feed a voltage signal into a bank of comparators with different reference voltages http://www.hardwaresecrets.com/article/317/6 http://www.allaboutcircuits.com/vol_4/chpt_13/8.html

  8. Computer Interfacing • LabView PCI or PCMCIA cards and connector board very common in research labs • http://www.ni.com • Lower cost: “Phidgets” have analog inputs and USB to PC • http://www.phidgets.com • Even cheaper, dedicated circuits such as the 1-Wire DS2450 converter • http://www.maxim-ic.com • And many more…

  9. Demos based on lab projects at U of L: 1-Wire and wireless sensor interfacing http://www.maxim-ic.com/products/1-wire/ “1-wire” chips allow multiple sensors to be connected to the same wire for weatherstations and similar devices. T(hermometer Demo) Wireless sensor board can poll multiple sensors on the 1-wire bus. (Flow sensor demo)

  10. Component identification quiz • Low stress (no grade but there’s a prize) • Circle answers on paper • In the event of a tie, we will have a drawing.

  11. Component Identification QuizQuestion 1:what is this? A 1 K resistor A 3.7 M resistor A battery

  12. Component Identification QuizQuestion 2:what is this? A ceramic capacitor A transistor An electrolytic capacitor

  13. Component Identification QuizQuestion 3:what is this? An electrolytic capacitor A ceramic capacitor A light-emitting diode

  14. Component Identification QuizQuestion 4:what is this? A. A transistor B. A voltage regulator C. Could be either A or B

  15. Component Identification QuizQuestion 5:what are these? A. Crystal oscillators B. Light emitting diodes C. Capacitors

  16. Component Identification QuizQuestion 6:what is this? A. A potentiometer B. An inductor C. A photocell

  17. Component Identification QuizQuestion 7:what is this? A. An integrated circuit B. A 555 timer C. Both A and B

  18. Component Identification QuizQuestion 8:what are these? A. Inductors B. Crystal oscillators C. Capacitors

  19. Component Identification QuizQuestion 9:what are these? Resistors B. Diodes C. Capacitors

  20. Component Identification QuizQuestion 10:what is this? A crystal oscillator A bouillon cube C. A DC-DC converter

  21. Component Identification Quiz done! Work on the project of your choiceUsing solderless breadboard first, then soldering if possible, is a good idea.“Troubleshooting” tips:Use resistance meter to check all pins are really connected how you wantCompare to a known-good circuit.Most parts are symmetrical, but sometimes polarity is important. Is it plugged in backwards/upside down/not at all? Project Time

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