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Lecture #2 Basic Electricity. Why learn electronics?. Ability to understand information sensor is providing Be able to read a wring diagram Basic understanding of what some components are doing in the circuit Troubleshooting!!!. Basics. Electricity is the flow of electrons

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why learn electronics
Why learn electronics?
  • Ability to understand information sensor is providing
  • Be able to read a wring diagram
  • Basic understanding of what some components are doing in the circuit
  • Troubleshooting!!!
  • Electricity is the flow of electrons
  • Many similarities with the flow of water
  • Water flows

because of a



  • Bigger pipes

allow more



A complete circuit is required for current to flow

  • Also required:
    • A source of “pressure” (voltage)
  • Optional:
    • Switch
    • Something to do work
  • Voltage
    • Electrical potential difference
    • Electrical “pressure”
    • Units
      • Volts (v)
  • Current
    • Flow of electron charge (phenomenon)
    • Rate of Flow of Electron charge (quantity)
    • Units
      • Ampere (A)
terms cont
Terms (cont)
  • Resistance: the resistance to flow
  • Friction in the pipe
  • Units
    • Ω – Ohm
  • Symbol
  • -WW-
simple equations
Simple Equations
  • Ohm\'s Law


      • E– Voltage (volts)
      • I – Current (amps)
      • R – Resistance (ohm)
  • Power


      • Watts
components resistors
Components: Resistors
  • Electronic component that provides resistance to the flow of electrons
  • Come in variety of sizes and ability to handle power
  • In Series
    • Resistance values (Ohms) add up to give total resistance
    • R1+R2+R3...=Rtotal
  • In Parallel
    • Each have same potential difference
    • 1/R1+1/R2...=1/Rtotal
using resistors
Using resistors


  • Voltage divider
  • Use Ohm’s law to calculate:
    • Current
    • Voltage between A and B
    • Voltage Between B and C
  • Assume:
    • R1 is 1000 Ω and R2 is 1000 Ω
    • R1 is 2000 Ω and R2 is 3000 Ω



special resistors
Special resistors
    • Variable resistor: 2 terminals
    • Examples
      • Audio control
      • Joysitck
      • Rheostat
  • Potentiometer: 3 terminals
    • Voltage divider
  • One-way valves
    • Allow current to flow in one direction
  • There is a drop in voltage across a diode
    • Drop is ~ 0.7V
  • Two main types
    • Single diode
      • Up to 100mA
    • Rectifier diode
      • Large Currents
  • Symbol
  • Used to separate battery packs
  • Also used to “idiot proof” connections
  • Called “diode isolation”
  • More later….
  • Light Emitting Diodes (LED)
    • Color is determined by the semiconductor material used
    • Still need to be connected in the correct direction
      • Current flow long to short
    • Easy to blow up
      • Limit voltage/current
  • Passive Electronic component
  • A pair of conductor separated by a dielectric
  • When a voltage is applied a charge builds up
    • Acts like a little battery
      • Why when you shut off certain things the light stays lit for a little even with no power
      • Eg. Computer power supply
  • Units: F - Farad
  • Symbol: -||-
  • Be very careful of very big ones……
  • In Series
    • The energy stored is equal to that of the other capacitors in the series
      • 1/C1+1/C2...=1/Ceq
  • In Parallel
    • Add up the capacitance
      • C1+C2+C3...=Ctotal
  • Opposite that of Resistors

Using capacitors:

  • Absorb voltage spikes
  • Tool used to test electronics (Main tool)
    • Voltage
      • Straight forward touch ends to terminals
    • Current
      • Need to put in sequence
      • Be sure you won’t exceed rating!!!!
    • Validity of a cable
      • “Ohm out”
      • Used to Identify the same

wire in a cable

dc vs ac
DC vs AC
  • Alternating Current (AC)
    • Polarity changes over time
      • Basic form is a sine wave
        • Other wave forms exist
    • Better for long distance transmission of power
      • High voltages – Low current
      • Pl=I2R
        • If current is doubled then 4x greater loss
    • Easily generated by a generator/alternator
      • Polarity changes as magnet spins
    • Can be “stepped up” and down using a transformer (more later)
    • Not used in Oceanographic instrumentation*
      • AC to DC converter almost always needed

*Not often, anyway

dc vs ac1
DC vs AC
  • Direct Current (DC)
    • Unidirectional flow of electric charge
    • Sources
      • Batteries
      • Solar Panels
    • Used in low voltage applications
    • More complicated then AC
    • AC can be converted to DC
  • using a rectifier


dc vs ac2
DC vs AC


what is electro magnetism
What is Electro-Magnetism?
  • Until 1821, only one kind of magnetism was known, the one produced by iron magnets.
  • Then a Danish scientist, Hans Christian Oersted discovered electromagnetism:
    • He noticed that the flow of electrical current in a wire caused a nearby compass needle to move.
    • The new phenomenon was studied in France by Andre-Marie Ampere,
    • He concluded that the nature of magnetism was quite different from what everyone had believed.
all magnetism is related to electricity
All magnetism is related to electricity
  • There thus exists two kinds of forces associated with electricity:
    • electric
    • magnetic.
  • In 1864 James Clerk Maxwell demonstrated a subtle connection between the two types of force
    • The connection involves the velocity of light.
    • From this connection sprang the idea that light was an electric phenomenon,
    • This led to the discovery of radio waves, the theory of relativity and a great deal of present-day physics.
  • If you use one wire to generate a changing field (AC), it will induce voltage in a nearby coil
  • You can isolate circuits this way
    • Works through plastic, glass, aluminum, water
  • But AC will also induce noise into adjacent wires
    • Shielding helps
    • Twisting wires helps
The voltage induced is determined by the ratio of the number of winds on the coil
    • So you can step up or step down
    • Only with AC
  • Used to turn things on and off (duh!)
  • But come in lots of flavors:
    • Momentary
    • Toggle
    • Rotary
    • poles
      • SPST: single pole single throw
      • SPDT: Single pole, double through
      • DPST: double pole, single throw
      • DPDT: double pole, double throw
      • Etc.
  • Electrically operated switches
  • Generally use an electromagnet to close a switch
  • End result: use a small switch (limited current capability) to operate a larger switch (with larger current capacity)
relay applications
Relay applications
  • Cars
    • Horn
    • Lights
    • Starter
  • Ocean:
    • Sensor power
    • Burn wires
    • Controller power
    • motors
  • “relays” made of semiconductors
  • Used to control circuits
  • Used to amplify signals
  • Replaced vacuum tubes
  • Gazillions of them in a computer
    • We’ll learn later how they are used in digital logic
how transistors work don t sweat the details
How transistors work(Don’t sweat the details)
  • Like two diodes back to back
    • No current can flow
  • But if you apply voltage to the middle layer, it ionizes (semi-conducts), allowing current through
  • More voltage = more flow
  • Variable “switch”
    • more like a valve
typical transistor circuit
Typical transistor circuit
  • Apply voltage to Vin to

make current flow

  • Note resistor
    • Combines with transistor to create a voltage divider
    • Result is using Vin to control Vout
    • But Vin may have VERY small voltage fluctuations while Vout has large fluctuations
analogue signal
Analogue Signal
  • Continuous signal
    • As that current changes the signal changes
    • Usually 0-5v, but can vary
      • Important when using analogue that your datalogger can handle the voltage produced by the sensor
  • Advantages
    • Infinite signal resolution
    • Can be processed by analog components
  • Disadvantages
    • Noisy
      • Shielded cable can help diminish the noise
    • Subject to loss in cables and connectors
digital signal
Digital Signal
  • Non-continuous signal
  • Two amplitude levels

called nodes

    • Digital logic
      • 0 or 1
      • True or false, yes or no, on or off
  • Fixed number of digits or bits
  • Sent as binary and needs a program to convert to “readable” values
analog to digital conversion
Analog to Digital Conversion
  • All analogue signals are converted to digital for processing
    • Resolution of the data depends on the A/D converter used
      • Signal is placed into bits
        • Stored in binary
  • Example – 12bit A/D converter
    • Range 0-5v
    • A/D resolution 12bits: 212 =4096 quantization levels
    • Analog voltage resolution is: 5V/4096
      • Meaning each “level” is equal to ~1.22mV/“level”
communications types
Communications types
  • Analogue
    • Direct signal
  • Digital
    • Serial
      • RS 232
        • Most common
        • 15m max length
        • 20kbs max speed
      • RS 485
        • 1200 max length
        • 100kbs @ 1200m
        • 35 Mbs @ 15m
    • Parallel: almost obsolete
    • Ethernet
      • Large data transfer
instruments require power
Instruments require Power
  • No Power No data
    • All sensors require power to operate, some more than others
  • How long with the sensor last?
  • How many sensors can I run off one datalogger?
  • Which batteries should I go with?
    • Rechargeable or primary (one time use)
  • How many batteries do I need?
powering marine instrumentation
Powering Marine Instrumentation
  • Two main options
    • Batteries
    • Sea cable
      • Power from ship or shore
      • Usually allows data to be “Live Feed” as well
sea cables
Sea Cables
  • DC Power from ship
    • Usually 12-15 volts
    • Power limited due to:
      • Slip rings
      • Distance
      • Surface power supply
    • Usually not limited by voltage
      • Depends on what is at the other end of the cable for interfacing the sensor
  • Majority of ship deployment setups use Sea Cables
sea cables1
Sea Cables
  • What if your sensor requires more power or higher voltage
    • Use a battery
    • but data may still be able to be sent up the sea cable
  • What if the ship only has one sea cable?
    • (Usually hooked to the CTD)
    • Bring your own sea cable
    • Use a battery