1. CircuitProtection,Tips, andTroubleshooting Fall 2014 ECE 445

2. Becominga GoodDesign Engineer Understand the problem Understand the constraints you have Understand previous approaches to the problem at hand End goal of senior design: – Solve problems you haven’t been faced with and be innovative But first: background knowledge is required

3. CircuitConnections Pay attention to polarity Longer Lead: Positive Electrolytic capacitor Shorter Lead: Negative BADGOOD

4. Ratings Determine part ratings All components are rated Capacitors: –If the voltage across the capacitor is going to be 50 [V], should you use a capacitor that is rated to 50 [V]? Resistors: maximum power dissipation P = i 2 * R or P = v 2 /R –Example: –P = (5e-3) 2 * 1e4 –i.e. the power dissipated without burning it out = 250 mW From Newark Electronics

5. Data Sheets By reading the data sheet: –Provide pin-layouts –Device ratings –Potential applications

6. Voltage CurrentLimiting Fuses: typically allow for passage of “ normal ” current A fuse will “ blow ” above its current rating Diodes: Conduct when V>0.7 V Best solution: use both diodes and fuses Fuses

7. Voltage/CurrentProtection Examples Fuses and Diode CombinationCurrent Limiting Resistor Current across resistor typically = 20 mA

8. Device Polarity The longer length is the (+) terminal Capacitor Polarity: tantalum or electrolytic (+) (-) The bar indicates cathode (+)(-) (+) Diode (+) (-) No polarity: ceramic or polyester (-) http://electrapk.com/zener-diode/http://academic.evergreen.edu/projects/biophysics/technotes/electron/leds.htm/

9. Reverse PolarityProtection Below are 2 different configurations to ensure correct voltage polarity to the circuit. “Diode Bridge” Circuit will operate under either polarity, but will have higher losses Circuit will not operate with incorrect polarity Wikipedia

10. PowerSupplyBypass/ DecouplingCapacitors Bypass capacitors Takes noise to ground Rephrased: basically shunts AC signals to ground Typical values range from: 0.1 uF Larger size capacitors for higher supply voltages *Picture http://www.physics.udel.edu/~nowak/phys645/The_bipolar_transistor_files/image013.jpghttp://www.physics.udel.edu/~nowak/phys645/The_bipolar_transistor_files/image013.jpg

11. Earth Groundvs “ Ground ” Earth Ground Floating Ground Green terminal is earth ground Black terminals are signal grounds Know the difference!

12. Potentiometers Variable resistors –Example is a trimpot with R=10 K Ohms –From (a) to (c), R1 = 6 K Ohms –From (b) to (c), R2 = 4 K Ohms (a) R1 = 6k To Rest of Circuit (c) (b) R2 = 4k

13. ResistorCodes METRIC-TO-AWG CONVERSION TABLE Metric Size mm 2 0.5 0.8 1.0 2.0 3.0 5.0 8.0 13.0 19.0 32.0 52.0 AWG Size 20 18 16 14 12 10 8 6 4 2 0 Resistor Value Chart Reading Surface Mount Resistors A resistor marked 332 is 3.3 kilo-ohms 3K3 is 3.3 kilo- ohms Know wire gauges

14. Wire Gauges Wire gauge is a standard for the size of the wire (proportional to current rating) Typical wire in lab is 22 AWG (American Wire Gauges) –52.9 mΩ/meter –7 A for short wiring –0.92 A for power transmission http://www.powerstream.com/Wire_Size.htm Breadboard in the lab can only use 22 AWG or smaller, otherwise it will damage the clips http://www.how-to-wire-it.com/romex-cable.html

15. DrivingHigh CurrentLoad Most microprocessor/TTL can drive <20mA, that is approximately an LED. –Interface microprocessor I/O with a gate. Let the gate break instead of the microprocessor! Methods –Relays may wear out and have delays –Transistor fast switching but have current limit –H-bridge allows forward and reverse current good for motors http://www.acroname.com/robotics/info/articles/drivers/drivers.html

16. TroubleshootingSteps (1/2) 1.Check supply voltage using the multimeter –Is power plugged in? Is any switch off? Is the fuse blown? Are all the breadboard bus strips connected to VDD/GND? 2.Probe signal at intermediate stages or individual function blocks I/O –Equipment available: For digital signals: Logic Analyzer, LEDs For analog signals: Oscilloscope, Voltmeter, Spectrum Analyzer 3.Check interconnections –Is anything mis-wired? Are any wires loose? Are any contacts bad? Is any signal floating?

17. TroubleshootingSteps (2/2) 4.Double check the design –Check the pin diagram –Check that you have the correct datasheet for the part number –Re-analyze the logic, go through some calculation –Ensure correct polarity (refer to the next slide) 5.Faulty devices/breadboard (Last resort if all else fails!) –Replace/rewire one part at a time, test after every change –Isolate the parts under test from the rest of the circuit

18. References http://www.intersil.com/data/an/ an1325.pdfhttp://www.intersil.com/data/an/ http://en.wikipedia.org/wiki/Diodehttp://en.wikipedia.org/wiki/Diode http://en.wikipedia.org/wiki/ Fuse_(electrical)http://en.wikipedia.org/wiki/ http://www.learnabout-electronics.org/ resistors_07.phphttp://www.learnabout-electronics.org/ http://www.rbeelectronics.com/ wtable.htmhttp://www.rbeelectronics.com/ Previous ECE 445 Lecture Slides Staff of the ECE Electronics Shop, Dan Mast, Mark Smart, Skot Wiedmann