Pat

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Pats Electronics Lecture

• basics

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Water Analogy (helped me)
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Water Analogy, contd
Water Pressure (the higher the pressure the more water flows) ? Voltage (The higher the voltage the more current flows)
Water Flow Rate (e.g. gallons per minute) ? Current (which is actually charge flow rate 1 coulomb/sec 1 ampere)
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Work

• In both pictures, potential energy is converted
  to work, where
• Work
• Kinetic energy
• Heat
• Some other kind of potential energy
• Physics note Total Energy is conserved

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Whats Happening

• Electric charges can flow in conductors
• Like charges repel
• Unlike charges attract

Because of the chemistry inside the battery,
there is a voltage set up across the terminals
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Whats Happening

• Electric charges can flow in conductors
• Like charges repel
• Unlike charges attract

If we connect wires, they also become charged up
- - -
- - - - - - - -
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Whats Happening

• Electric charges can flow in conductors
• Like charges repel
• Unlike charges attract

charges
charges
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Whats really happening

• Electrons are flowing out of bottom of battery,
  around to the top
• Since they are negative, the direction of the
  current flow (by convention) is opposite their
  physical movement
• It is MUCH EASIER to think of positive charges
  flowing, even though they are slightly fictitious

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Typical Elements of a circuit

• Wires
• Voltage Sources
• Electronic Components
• Resistors
• Capacitors
• Inductors
• Modular circuits (e.g. amplifiers)
• Occasionally diodes and transistors

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Wires

• These are good conductors, with practically
  unimpeded flow of current
• Electrons in metal form a kind of plasma
• Any flowing current creates a magnetic field
  (which btw can be used to measure the current)
• Size is measured by AWG, American Wire Gauge,
  since the 1850s

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Interesting note on AWG

• The gauge number is similar to decibel
  measurement for sound
• 20 steps in AWG is (almost) a factor of 10 in
  wire diameter
• For instance, 1 AWG wire is 10x the diameter
  of 20 AWG
• We typically use 20 to 24 for circuits

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Voltage

• (the Electrical version of pressure)
• Measured with a meter, if time variation is slow
  enough
• Measured with a scope and typically a scope probe
  if fast time variation
• Hazards
• HIGH VOLTAGE CAN KILL YOU
• (actually its the current through your heart)

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Pressure is not exactly Voltage

• One difference voltage is always measured
  between two points (e.g. a meter has a common
  probe and a measurement probe.
• The reason for this goes back to the attraction
  of charges,
• Still a very good analogy, though

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Water flow is not exactly Electrical current

• Water can flow even when there is not an
  (obvious) return path

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2 hazards we will encounter

• 1 DO NOT USE A SCOPE OR METER TO MEASURE THE AC
  LINE VOLTAGE!!!
• (what is AC voltage? We will cover this)
• WHY?
• THE METER CAN LITERALLY EXPLODE
• You might kill a 10,000 scope
• ? ? ?Use a Wiggy instead

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2d hazard Death

• High voltages in our lab can kill you.
• Best case scenario you accidentally touch a high
  voltage terminal, and current starts to flow
  through your arm. If this current is much larger
  than your nerve impulses, you can no longer pull
  your arm away, because your muscles dont receive
  the command. It hurts. You begin to think about
  how dumb you were to have one hand resting on
  ground while you poked around with the other one.
  Next, some guy who also didnt listen grabs onto
  you to try to pull you away. Current flows
  through him, too, so he is useless. Finally
  someone who paid attention to this lecture finds
  a non-conducting hook and saves both victims.
• Worst case sufficient current finds its way
  through your heart to stop it, too.

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High Current

• This can also be dangerous
• wires can heat up, and cause fires.
• Circuit elements (wires) can literally explode if
  a lot of energy is dumped into them quickly
• More subtly, interrupting a high current can give
  a high-voltage transient!!! Of all the hazards,
  this is the only one I personally had experience
  with that actually did kill a guy.
• (We will get to the reason for this.)

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Resistors

• Resistors impede the flow of electrical current
• Like a pin-hole for water flow

Water source
High pressure Lower pressure

• Constriction in pipe
• resists the water flow ?
• need more pressure to get the same flow
• pressure after the constriction is lower

Similarly, there is a voltage drop across a
resistor when current flows through it.
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Resistors

• Symbol
• Measured in ohms
• A resistance of 1 ohm will let 1 Amp of current
  flow for a voltage drop of 1 Volt (across the
  resistor).

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Ohms Law
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Computing resistance

• Resistance
• Where ? (rho) is the resistivity of the
  material
• L is the length
• A is the area

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Some Resistivities
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Resistor Marking

• Color Code
• First 2 bands digits
• 3d band power of 10
• 4th band tolerance gold 5, silver 10, none
  20
• E.g. brown black red is
• 1 0 00
• (a one followed by a zero followed by
  2 zeros)
• Other Notes
• 3d band gold divide by 10
• 3d band silver divide by 100

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Remember

• Black 0 (no color)
• White 9 (all colors)
• Grey is close to white, so make it 8
• Brown ? Might as well be 1
• The rest correspond to the spectrum
• ROYGBV (You may have heard of this guy Roy
  G. Biv)
• Red 2etc.

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From http//www.token.com.tw/resistor/image/color-
code.jpg
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Simple Circuit Diagrams 1

• 1 Voltage Source (e.g. battery)
• 1 resistor
• Given a 9 V battery, and a 1000 ohm resistor,
  what current will flow?

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Simple Circuit Diagrams 2

• Resistors in series

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Simple Circuit Diagrams 3

• Resistors in parallel

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Convenient formulas

• Series resistors
• Parallel resistors

Note it may help to think about the construction
of a resistor
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Another circuit
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think about what happens in this arrangement
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What about this one?
Hint symmetry helps
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Other useful components

• Inductors
• Capacitors
• Diodes
• Integrated Circuits (e.g. RF amplifier)
• MOSFETs
• Occasionally transistors
• Rarely vacuum tubes

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Electrical Power

• Power is rate of dissipation of energy
• Also rate of getting work done

• Energy is conserved, so if we are not storing any
  energy
• Power in Power out heat dissipated as losses

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AC Voltage, Current

• AC stands for alternating current
• Nevertheless people still talk about AC current
  coming out of the wall.
• The voltage alternates if you had a really fast
  meter, you would see the polarity reversing 60
  times a second

Or just use an oscilloscope, BUT DONT HOOK IT
UP DIRECTLY
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Water analogy

• 2 buckets on a see-saw

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Water analogy

• 2 buckets on a see-saw

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Why AC?

• See War of Currents on wikipedia
• Edison wanted DC
• Tesla wanted AC
• No good way to transform DC to a different
  voltage (at least in 1900)
• Transmission requires high current
• Must generate near point of load
• AC can be transformed up to high voltage, low
  current, for transmission, then back to safer
  levels (110 V) near point of load

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AC Outlet 110 V (rms)
Low side, or neutral
High side, or line
Ground
In an AC line cord, standard colors are Green
for ground, White for neutral, and Black for line
NOTE in most AC wiring, BLACK is the hot, or
high voltage, side
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AC Voltage Measurement

• Level is quoted as
• Peak-to-peak (least ambiguous)
• Peak
• RMS root mean square, which is the average
  value of the square of the voltage. This is what
  a typical handheld voltmeter reads on the AC
  setting.
• 110 V is the RMS value, peak is around 160 V, or
  

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Transformer

• 2 sets of windings, with their magnetic fields
  coupled.
• Use iron to channel the field from one set to
  another
• Step up or down the voltage according to the
  turns ratio

primary winding
secondary winding
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Transformers, conts
where
Also
Note Power is conserved
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Capacitors

• Symbols
• Let AC through, but not DC another way of saying
  this is that they tend to keep the voltage across
  them constant
• Have an impedance (not a resistance because they
  dont dissipate any power)

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Capacitor construction
2 conductors separated by a physical space
d A
C, in Farads, is a measure of how much charge can
be stored for a given voltage
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Water Model

• Water balloons in a sealed oil-filled enclosure

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Water Model

• Water balloons in a sealed oil-filled enclosure

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Water Model

• Water balloons in a sealed oil-filled enclosure

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Water Model

• Water balloons in a sealed oil-filled enclosure

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Capacitors, contd

• Often the gap is filled with a dielectric
  material to increase the capacitance using an
  insulator also allows the gap to shrink, d ? 0,
  but voltage stays the same without breakdown.
• All dielectrics have a safe operating voltage,
  which is given as the voltage rating
• Sometimes the dielectric can only be charged in
  one direction the capacitor is polarized, or
  electrolytic advantage is higher capacitance
• Ugly fact that we will not worry about most
  dielectrics change their value as they are biased
  to higher voltages!

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Inductors

• Symbol
• Let DC through, but not AC another way of saying
  this is that it tends to keep the current flowing
  through it at a constant level
• Have an impedance (not a resistance because they
  dont dissipate any power)

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Inductor Construction

• Any coil of wire
• Sometimes iron is added to increase the magnetic
  stored energy, which increases the inductance

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Inductance

• Why N2 ?
• Current flowing through the windings produces a
  magnetic field more turns produces more field,
  proportional to the number of turns in a given
  length.
• Each turn then picks up voltage from the
  changing magnetic field with the turns in
  series the voltage adds, so the total is
  proportional to the total number of turns.

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Example circuit

• Initially the switch is open, so no current is
  flowing
• Close the switch the inductor tends to keep the
  same current flowing, which is zero.
• Eventually the inductor looks like a wire, so the
  current is given by Ohms law I V R

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Water analog heavy paddle-wheel
1. Once valve is opened, paddle-wheel begins to
spin
2. Paddle-wheel has heavy flywheel attached so
it is hard to spin up, but once it is spinning it
tends to keep going
Valve
Flow
3. Eventually the paddle-wheel gets up to speed,
and the flow is limited by the resistance in the
line
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Another circuit the dangers of high current

• Initially the switch is open, so some current
  flows, such that I V R
• Close the switch current starts to increase
• Suppose the current builds up to 100x its initial
  value, then the switch is opened what happens?
• Inductor tries to keep the same current flowing,
  so initially V 100x the battery voltage

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Generating high pressure due to current flow
Suppose valve is initially closed
Paddle-wheel is spinning slowly
Flow
Valve
Then we open the valve for some amount of time,
letting the flow build up (paddle-wheel spins
faster)
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Generating high pressure due to current flow
The pressure ahead of the resistance goes up,
since the paddle-wheel keeps spinning eventually
slows down to steady state
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Diodes

• Symbol
• Function only let current flow one direction
• Convert AC to DC useful for power supplies,
  detecting radio signals,

Pos Neg
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Water Analog of a diode

• A flap inside a pipe
• flow no flow

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SOLDERING

• Solder works by forming a solution of the metals
  being joined in the liquid solder.
• So the solder needs to be hot enough to flow,
  BUT
• Too much heat traveling up the leads will destroy
  semiconductors!
• The work pieces rather than the soldering iron
  must melt the solder
• When done, the two conductors being soldered
  should look wetted

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Solder wire
Has flux inside. Flux is a wax-like goo that
has a few percent acid, for cleaning the oxide
layer from wires being soldered. For plumbing,
the same thing happens except the flux is usually
applied separately. And you cant use lead solder
anymore. And usually a torch is used instead of
an iron.
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Soldering Hints

• Liquid solder conducts heat better than a dry
  tip, so it helps to put a dab of solder onto the
  tip before soldering. The associated flux can
  also help clean up the tip.
• It helps to tin the leads being soldered
  individually before actually trying to solder
  them together.
• The smoke comes from burning flux, not lead, but
  still probably not healthy to breathe it in.
• Dont hold solder in mouth.

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Soldering Irons - experience

• Temperature regulated ones are crucial
• Tips are special if you decide that you want a
  sharper tip, you can sand the tip down to a
  point, but it will dissolve a little bit each
  time you use it and disappear before too long.

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Solder joint cross section
From http//www.emeraldinsight.com/fig/21702503060
01.png
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Making a Circuit Board

• Generate a layout, using some kind of PCB
  software. There are programs that are free but
  that I know very little about (we use a bad but
  expensive tool, which is not even sold anymore)
• Eagle, from http//www.cadsoftusa.com/
• Kicad, from http//www.lis.inpg.fr/realise_au_lis/
  kicad/

Top
Bottom
For our process, we generate a positive image
colored parts (which print as black) will be
copper, white parts no copper.
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Circuit Board, contd

1. Use laser printer to print layout (also called
   artwork) on a transparency
2. Align top and bottom, and tape them together.
3. Slip a pre-sensitized board between them.

Top transparency
Bottom transparency
Circuit board, has copper on both sides, covered
with photo-resist.
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Circuit Board, etching

1. Expose in UV box for 5 minutes. The UV goes
   through the clear parts of the transparency, and
   does something to the photoresist.
2. Soak board in developer this washes off the
   exposed photoresist. (Dilute the developer
   solution 1 part developer to 10 parts water.)
3. Rinse developer off using water
4. Etch in Ferric Chloride solution. The
   photoresist that is still on the copper prevents
   the copper from being etched, at least for a
   while. Etching usually completes in 15-45
   minutes, depending on how old the solution is.
   You never know, so you need to keep an eye on the
   progress.

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Circuit board fab cautions and notes

• The ferric chloride solution will irritate your
  skin after a few minutes, so a little is OK but
  generally you should rinse it off.
• It will also eat holes in your clothes, if it
  gets on them and dries there. (? mysterious
  little holes next time you wear them)
• There is an aquarium heater and a bubbler in the
  ferric chloride tank, to help speed things up
  remember to turn it off.
• Dont pour ferric chloride down the copper drain
  pipes.