Embedded Control. Week 1 (6/29/11)

Transcription

1 Embedded Control Week 1 (6/29/11)

2 Week 1 15:00 Lecture Circuit theory, terminology Overview of elementary circuit components Reading circuit diagrams 16:00 Lab NXT GPIO with HiTechnic sensor expansion kit

3 Circuit Theory Voltage, V Potential difference Difference in voltage between the cathode (+) and the anode ( ) of a voltage supply Measured in Volts (V) Current, I Time derivative of voltage Measured in Amperes (A) Alternating Current (AC) Current flow alternates (reciprocates) between the cathode and anode Direct Current (DC) Current flows in a single direction from the anode to the cathode Energy, E Electrical work Measured in Joules (J) Power, P Time derivative of energy Directly proportional to both voltage and current Measured in Watts (W) I d dt V V d P E E dt 2 P V I I R

4 Elementary Circuit Components Resistor Capacitor Diode Switch Battery

5 Resistors Resist the flow of current Directly proportional to voltage; inversely proportional to current (Ohm s Law) V R I R V I Measured in ohms (Ω) Non-polar terminals I V Resistivity resistance per unit length R

6 Reading Resistors Color band system Each color band represents a number Second-to-last color band represents a base 10 resistance multiplier Last color band represents resistor tolerance

7 Reading Resistors - Problems What are the indicated resistances? What are the color bands? 4.7kΩ 390Ω 1.5Ω 0.56Ω 62MΩ

8 Reading Resistors - Solutions What are the indicated resistances? 2.7Ω 360kΩ 0.47Ω 75Ω 910Ω What are the color bands? 4.7kΩ 390Ω 1.5Ω 0.56Ω 62MΩ

9 Networks of Resistors Series configuration Total resistance is the sum of each individual resistor n R t R i i1 Total resistance is always greater than that of any individual resistor Parallel configuration Total resistance is the inverse of the sum of the inverse-resistance of each individual resistor n R t R i i1 1 1 R1 R2 Total resistance is always less than that of any individual resistor R n R 2 R 1 Rn

10 Kirchhoff s Laws of Current and Voltage Law of Current The magnitude of the sum of the currents entering and exiting through a node is zero n k 1 I k 0 Law of Voltage The sum of the potential differences around a closed circuit is zero n k 1 V k 0 I 1 I 3 V A I 2 I 4

11 Kirchhoff s Laws of Current and Voltage Problems What are the unknown currents? 2A 3A? 5A 1A? 11A 2A?? 6A 3A 6A What is the voltage at the indicated points? 5V 1kΩ 4kΩ 0V 5V 4kΩ 1kΩ 1kΩ 50kΩ 2kΩ 0V 5V 10kΩ 50kΩ 30kΩ 0V

12 Kirchhoff s Laws of Current and Voltage Solutions What are the unknown currents? 2A 3A 5A 5A 1A -8A 11A 2A 4A -2A 6A 3A 6A What is the voltage at the indicated points? 0.5V 5V 4kΩ 5V 1kΩ 4kΩ 0V 1kΩ 1kΩ 4V 4.23V 2.31V 0V 50kΩ 2kΩ 5V 10kΩ 50kΩ 30kΩ 0V

13 Variable Resistors Change resistance as a function of an external input Rheostats Resistance changes as a function of contact position Photo-resistors Resistance changes as a function of ambient light Strain gauges Resistance changes as a function of length

14 Potentiometers Length of resistive material shorted by a contact Effectively separates the resistor into two resistors Voltage divider outputs a voltage between that of the reference voltages as a function of the contact position Voltage changes linearly as a function of contact position R1 R2 V R 1 O V CC R R 1 2 GND VO VCC

15 Capacitors Store and release charge Directly proportional to charge; inversely proportional to voltage Measured in Farads (F) Polar or non-polar terminals Electrolytic polar Ceramic non-polar + C E E Q V 1 VQ 2 1 CV 2 2

16 Networks of Capacitors Series configuration Total capacitance is the inverse of the sum of the inverse-capacitance of each individual capacitor 1 1 n C t C i i1 C1 C2 Cn Total capacitance is always less than that of any individual capacitors Parallel configuration Total capacitance is the sum of the capacitance of each individual capacitor + n C t C i i1 + + Total capacitance is always greater than that of any individual capacitor + + C n C 2 C 1 +

17 Diodes Allows unidirectional current flow Polar terminals Types of Diodes LED - Light Emitting Diode Linear voltage regulators - Regulate voltage from a variable power source AC to DC conversion circuit

18 Switches Opens or closes a circuit through mechanical action ON/OFF Single pole, single throw (SPST) 2 leads ON/OFF/ON Single pole, double throw (SPDT) Three leads Contact bouncing Chatter in the signal due to mechanical closing/opening action and arcing of electricity

19 Pull-Up/Pull-Down Resistors Pull-up resistors Pull up voltage to Vcc level when circuit is open Input is held high until circuit is closed VCC GND Pull-down resistors Pull down voltage to GND level when circuit is open Input is held low until circuit is closed GND V CC

20 Batteries Create a potential difference to drive circuits Supplies power to circuits Voltage and current are relative to the battery power P V I I 2 R

21 Lab Interfacing circuit components with the LEGO NXT Brick Building simple circuits using the HiTechnic sensor expansion kit

22 LED Source Part Name Value Resistor R1 220Ω Diode D1 LED B0 R1 D1 GND

23 LED Source Lab Setup NXT Protoboard LED

24 LED Source Circuit The digital pin B0 connects to the current-limiting resistor The LED connects from the currentlimiting resistor to GND

25 LED Source Output The program LED_Source_Sink.nxc cycles the digital pins on the proto-board The board sources current to illuminate the LED, which is limited to about 20 ma

26 LED Sink Part Name Value Resistor R1 220Ω Diode D1 LED 3V R1 D1 B0

27 LED Sink Circuit The 3.3V output connects to the current-limiting resistor Protoboard The LED connects from the resistor to the digital pin B0 LED The LED output is similar to the LED Source lab The digital pin can sink much more current than it can source

28 Pull-Down Resistor GND Part Name Value Resistor R1 220Ω R2 220Ω 3V S1 R1 R2 A0 Diode D1 LED Switch S1 SPST D1 GND

29 Pull-Down Resistor Lab Setup and Circuit NXT Protoboard LED Switch

30 Pull-Down Resistor Lab Output The analog pin A0 reads the normalized voltage (10-bit, 0 to 1023) When the switch is open, the pin registers 0; when the switch is closed, the pin registers 1023 When the switch is pressed, the LED illuminates

31 Pull-Up Resistor 3V Part Name Value Resistor R1 220Ω Diode D1 LED Switch S1 SPST GND S1 R1 A0 D1 GND

32 Pull-Up Resistor Lab Setup and Circuit NXT LED Protoboard Switch

33 Pull-Up Resistor Lab Output When the switch is pressed, the LED dims and the analog input pin registers 0 When the switch is released, the LED illuminates and the analog input pin registers ~561 (voltage drop across the pull-up resistor)

34 LED Dimmer Part Name Value Resistor R1 10kΩ R2 220Ω 3V R1 A0 GND Diode D1 LED R2 D1 GND

35 LED Dimmer Lab Setup NXT LED Protoboard Trimming Potentiometer

36 LED Dimmer Circuit Protoboard LED Trimming Potentiometer

37 LED Dimmer Output Use a Phillip s head screwdriver (+) to turn the dial on the potentiometer The LED will illuminate at around 550 and become brighter thereafter

38 Photo-Resistor 3V R1 A0 D1 Part Name Value Resistor R1 - R2 10kΩ Diode D1 LED R2 GND

39 Photo-Resistor Lab Setup NXT Protoboard LED Photo-resistor

40 Photo-Resistor Circult Use a Phillip s head screwdriver (+) to turn the dial on the potentiometer Protoboard LED Photo-resistor

41 Photo-Resistor Output Shine light on the photo-resistor to brighten the LED