Electronics Gauntlet
Definition: a gauntlet is a series of tests or
trials. See the exquisitely bad movie by Clint
Eastwood and his slatternly co-conspirator in
bad taste, Sondra Locke.
Purpose: so LSU graduate chemistry students are able to solve VERY minor problems
and talk with professional electronics personnel intelligently to resolve issues or design
components for their research.
Limitations: this is JUST the very most basic stuff. Smart people spend years learning
electronics, just as you have done with Chemistry. We just want you to be able to have
an intelligent conversation with those people…and not make silly requests of them by
fixing it yourself whenever convenient.
Safety:
 When in doubt, do not touch!
 Keep one hand in your pocket! (Keeps current from traversing your heart).
 DC voltages produced by flashlight batteries (or even car batteries) is OK.
 Avoid DC voltages and most AC voltages.
 Most equipment takes a while to discharge after you turn it off!
DC vs. AC
 DC: direct (or steady) current or voltage. Example: battery.
 AC: alternating current or voltage. Example: house electrical outlets.
DC
AC
current, i
time, t
Why both? Many everyday devices, such as computers, really want DC. But
transmitting DC over long distances (from an electrical power plant) is inefficient
and wastes energy. The power plant therefore produces AC, which is fed to the
computer, which converts it to DC. Other devices (many motors) use AC
directly.
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Units Reminders
Quantity
Symbol
Unit
Charge
Usually q or Q
Current:
i or I
Potential:
Resistance:
V
R
Capacitance:
Inductance:
C
L
Coulombs (too bad—other
units would make more sense)
ampere (one coulomb per
second)
volts (one Joule per coulomb)
ohms (one volts per ampere, or
JoulesecCoulomb-2)
farads (one Coulomb per volt
henry (volt-sec per ampere)
Unit
Symbol
C
A
V

F
H
Some relations
V = IR (voltage equals current times resistance)
P = IV (power in watts is current in amperes times voltage in volts)
P = I2R
P = V2/R
C = Q/V (capacitance descries how much charge you can hold in the device—it’s
capacity!—for each volt applied)
V = L (di/dt) (voltages build up when the current changes—one reason it is hard
to make faster and faster computers).
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Components
Electron-controlling devices, or electronic components, can be divided into “passive” and
“active”.


Passive: no power gain as the electrons flow through (resistors, capacitors,
inductors).
Active: able to control the amount of electrons flowing (diodes, transistors, etc.)
Symbols
In diagrams of electrical devices, the various components are indicated by
symbols. Below is a picture of some resistors and the symbol:
In this Gauntlet, we are just going to show you how some components look.
For more symbols and pictures of components, see:
http://webhome.idirect.com/~jadams/electronics/oldindex.htm
Values
Component values are usually indicated on the device—e.g. 50 F for a 50 x 10-6 Farad
capacitor. Resistors follow a color code:
The approximate value of a resistor can be determined from its color code, as shown
below:
Third Band
First Band
Example: a resistor whose bands
are red, orange, yellow and gold is:
23  104  5% (i.e., 230 k)
Fourth Band
Second Band
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Resistor Color Table
Color
First Band
Second Band
Third Band
black
brown
red
orange
yellow
green
blue
violet
gray
white
gold
silver
0
1
2
3
4
5
6
7
8
9
---
0
1
2
3
4
5
6
7
8
9
---
100
101
102
103
104
105
106
107
108
109
10-1
10-2
Fourth band: Silver is:
Gold is:
no band is:
10%
5% tolerance
20% tolerance
This table taken from: Diefenderfer: Principles of Electronic Instruments, Saunders:
Philadelphia, 1972. Call # TK7878.4 D5
Circuits
Electrons flow from regions of high to low potential. The voltage change all the way
around such a circuit is zero (one of the Kirchoff’s laws from your Physics class). We
don’t need to know much about circuits here, but this one should look familiar:
i
R1
R2
The battery on the left side provides counterclockwise current and a voltage, V. The
resistors, R1 and R2, provide voltage drops V1= iR1 and V2 = iR2, respectively. The total
voltage around the loop is zero: V - iR1 - iR2 = 0. You will use this circuit to reduce a
voltage in one of the gauntlets.
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Gauntlet Part #1a: Passive Components
Into the rectangle, place five samples of the component that
follows the equation shown.
Equation: V = IR
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Place this paper next to the page holding
the passive components that follow this
type of frequency response curve:
Gain
Hz
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Gauntlet Part #1b: Passive Components
Into the rectangle, place five samples of the component that
follows the equation shown.
Equation: C = Q/V
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Place this paper next to the page holding
the passive components that follow a
frequency response curve like this:
Gain
Hz
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Gauntlet Part #1c: Passive Components
Into the rectangle, place five samples of the component that
follows the equation shown.
Equation: V = L (di/dt)
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Place this paper next to the page holding
the components that follow this
frequency response curve:
Gain
Hz
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Put this symbol next to the correct components &
frequency response curve
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Put this symbol next to the correct components &
frequency response curve
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Put this symbol next to the correct components &
frequency response curve
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Gauntlet Part 2: Identifying a blown fuse.
An instrument that was working yesterday suddenly stopped. After unplugging, it was
opened up and the following four fuses identified. Checking fuses is the first thing to try!
In this case, only one of the four fuses was bad. Which one?
A
B
C
D
Fuse hints:
 you can SOMETIMES tell if a fuse is broken just by looking. But fuses that
sometimes LOOK good are NOT. You should always test good-looking fuses
with a meter.
 Always replace the fuse with one of the same value and speed (for old gear, try to
check that the correct fuse was installed—i.e., that nobody screwed up before you
got to the instrument).
 If the fuse blows again quickly, something more serious is wrong. Get help!
 The voltage rating on fuses just indicates the normal operating voltage maximum:
the fuse will not arc at voltages lower than the indicated. It is current, not voltage,
that causes the fuse to blow.
 Fuses have other shapes, but the simple cylindrical ones above are common.
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Gauntlet, Part #3. How much heat?
If the Variac is doubled from 20 to 40,
how much does the rate of heat
production increase?
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Gauntlet Part #4. Measure that voltage!
In some applications, a signal exceeds
what your meter (or oscilloscope, or the
A-D card in your computer) can
measure. You may have to passively cut
the voltage down.
WITHOUT TWIDDLING THE METER
(or oscilloscope knobs or A-D card
settings) make a circuit that enables you
to get this reading.
Application note: a typical application of this
resistive network is to operate a photodetector in its
optimum range. A very sensitive detector may
produce too much voltage for a computer A-D to read
it correctly. It’s tempting to reduce the light striking
the detector, but this may just lower the signal down
into the (constant) noise range. It’s better to let the
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detector produce a large voltage well above the
noise….and measure a part of that large signal.
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Gauntlet Part #5a: Active Components
Into the rectangle, place one or more samples of the component
listed below.
Transistors
(mnemonic: transistors, like tripods, have three feet)
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Gauntlet Part #5b: Active Components
Into the rectangle, place one or more samples of the component
listed below.
Operational Amplifiers
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Gauntlet Part #5c: Active Components
Into the rectangle, place one or more samples of the component
listed below.
Diodes
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Gauntlet Part #5
(Place the cutouts on the page with the
appropriate components)
i
V
Several are
Electronic
used to
“checkvalve” convert AC to
DC
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i
C
B
V
E
Electronic
Stopcock
A small
applied signal
results in huge
output change
Not all that
different from First invented
tubes, or as
1923
the British
Forgotten
call them,
Reinvented
Valves
~1948
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Changing
resistors
attached to
pins affects
gain.
Easily used
to add,
differentiate,
multiply,
etc.
Integrated
Circuit
23
Typically
Can cure
contains 20
impedance
Transistors and mismatches,
11 Resistors,
making
less than $1 instruments
more
compatible.
Introduced
1968
741
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Gauntlet Part #6: THE MIT TEST
A study showed that most MIT engineers
could NOT make a flashlight! Said one,
“I’m a mechanical engineer!”
Using the components below, assemble a
flashlight with a working switch.
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Gauntlet Part #7 Woofer Tester
The woofer tester is used to guess at the
contents of some passive components in
a sealed, black box. Students are
encouraged to guess it first, then open to
see if they got the components right.
They may try various other components
in series, parallel, etc.
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Appendix: AC Circuits
In the above, we mostly just have component identification
and hints of the theory—e.g., voltage across inductor =
Ldi/dt. It makes good sense for polymer people to study a
little AC circuit theory, because it echoes the development
of rheology. A very nice web reference for AC circuits
appears here:
http://www.phys.unsw.edu.au/~jw/AC.html
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Appendix: TA Prep Notes
Requires
soldering irons, solder
boxes of passive/active components
batteries
switches
lightbulbs
variac
heating mantle
printouts of the gauntlet
blown fuses with tape over them
optional: mystery components potted in clay; use frequency response or phase to determine what
they are.
Set up a signal generator feeding an oscilloscope; set the input to be too large for the oscilloscope.
Have resistors and a potentiostat nearby, so students can construct voltage divider circuit. Let the
experiment with inductors and capacitors, too.
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