Electronics, Sensors, and Actuators 4/14/15 David Flicker BE107
Overview Basic electronics and components Sensors Actuators
Electronics 101 Voltage, V, is fundamentally how much energy is gained or lost by a unit charge when it moves between two places Typically call the most negative part of the circuit, ground, to make all circuit voltages positive Can be used to transmit power and information through circuits
Electronics 101 Current, I, is how much charge passes by a specific point per unit time Also used for transmitting power and information through circuits How are voltage and current related?
Electronics 101 Simplest relationship is the resistor, V = IR
Electronics 101 Voltage Divider Pullup / pulldown resistor
Electronics 101 Capacitors Resist change in voltage by providing current to a circuit Stores charge on two plates separated by a dielectric
Electronics 101 Most common use is decoupling capacitors
Electronics 101 Inductors Resist changes in current by providing voltage to the circuit These voltages can become very large if not dissipated in some way
Electronics 101 The most common use of inductors is for models of motors Motors are effectively large inductors that also turn They are also used in DC/DC converters, power supply filtering and noise suppression
Electronics 101 Diodes Allow current to flow in only one direction With enough negative voltage, they do fail however Have a minimum voltage before current will start to flow
Electronics 101 The most popular applications is LEDs Need current limiting resistor
Electronics 101 Another use of diodes is flyback diodes to protect circuits from inductors
Electronics 101 Bipolar junction transistors (BJTs) Current controlled, current source Two flavors: NPN and PNP
Electronics 101 The current from the base to the emitter controls the current flowing from the collector to the emitter (in NPN) Emitter to base for PNP
Electronics 101 Field effect transistors (FETs) Voltage controlled current sources Two flavors: N channel and P channel (same as NPN and PNP BJTs respectively)
Electronics 101 Voltage on the gate controls the current from drain to source
Electronics 101 FETs are generally prefered to BJTs for the following reasons: Easier to use, just supply voltage to the gate No power used to keep the transistor on (BJTs need base current to always be flowing) Lower power dissipation when on
Sensors Now that we know a little about electronics, what can we sense Light Sound Motion Touch Flex Pressure Distance and many more!
Electronics 101 Comparator Only integrated circuit (ie chip) we will use this week Vout = HIGH if Vin > Vref, LOW otherwise Built using transistors internally
Light sensors For brightness measurements CdS cells (light dependent resistors) Phototransistors BJTs where the base current is provided by light
Image sensors Besides brightness, can also capture an image using an imaging sensor like in a webcam or digital camera
Motion sensors Can measure accelerations, rotation rates, and magnetic fields using the same chips in your smartphone Physically, have very small silicon masses moving around on a chip!
Touch sensors Two main options Buttons Capacitive sensing Smartphone screen
Flex sensor Flex sensor measures how much the sensor is bent by changing resistance
Pressure sensor Pressure sensor outputs a voltage proportional to how much pressure is applied
Distance sensors Send ultrasound or laser light out and determine how long it takes to reflect and return to the sensor
Sound sensors Also known as a microphone
Actuators So now we can sense the world, how can we actuate on it DC brushed motors DC brushless motors Servos
DC brushed motor Cool Gif A DC brushed motor is just an inductor
DC brushed motor How can we make it go in reverse? An H-bridge
DC brushed motor How can we slow it down? Reduce the current using a resistor? It is LAME because it just wastes power in the resistor Also, at low current, the motor just won t start turning
DC brushed motor Instead use Pulse Width Modulation (PWM) Rapidly turn the motor on and off (~1 khz) Eliminates both problems!
DC brushless motor Use transistors to commute (switch polarity) the motor instead of physical brushes
DC brushless motor To drive a brushless DC motor, we use an electronic speed controller (ESC) It contains the transistor and intelligence to control the motor Send it a pulse width to control its speed and direction
DC brushless motor Send a varying pulse width to the ESC to control it Same signal used to control servos
Servos Used to move something to a specific angle Uses the same pulse width signal as ESCs
Questions? Don t let out the magic smoke the makes electronics work!