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 wireless sensor deployment: UMASS BOSTON Center for Coastal Environmental Sensing Networks Example of a wireless sensor computer interface (Crossbow)

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 Digitize an analog signal Debounce a flickering signal such as a button press And similar operations

5. For common signal conditioning problems, your work is done. “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) Gain = (1+ R B /R A ).

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 Feed a voltage signal into a bank of comparators with different reference voltages 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. http://www.hardwaresecrets.com/article/317/6http://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 “1-wire” chips allow multiple sensors to be connected to the same wire for weatherstations and similar devices. T(hermometer Demo) http://www.maxim-ic.com/products/1-wire/ 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 Quiz Question 1: what is this? A.A 1 K resistor B.A 3.7 M resistor C.A battery

12. Component Identification Quiz Question 2: what is this? A.A ceramic capacitor B.A transistor C.An electrolytic capacitor

13. Component Identification Quiz Question 3: what is this? A.An electrolytic capacitor B.A ceramic capacitor C.A light-emitting diode

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

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

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

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

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

19. Component Identification Quiz Question 9: what are these? A.Resistors B. Diodes C. Capacitors

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

21. Component Identification Quiz done! Work on the project of your choice Using 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 want Compare 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