Circuits and Electronics (in a Nutshell)

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Circuits and Electronics(in a Nutshell)

• AEM 1905, Fall 2008

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Electrical circuits are a lotlike (water)
plumbing systemsin which water circulates
(except discharging of wateroutside of the
closed pipingsystem is not allowed).
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Electrical current consists of charged particles
(usually electrons) flowing through metal wires
like water current consists of water molecules
flowing through hollow pipes.
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Electrical current is defined as flowing from
positive to negative (also known as from high
voltage to low voltage) just like water flows
from regions of high pressure to regions of low
pressure.
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A battery can push electrical current through a
circuit (which is a continuous connection of
wires and components) just as a water pump can
push water through a closed plumbing system.
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The amount of electrical current is measured in
amperes (amps) and the pressure with which it
is pushed is measured in volts (V) just as water
current can be measured in gallons/minute and
water pressure can come in pounds/square inch
(psi).
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One needs to have a complete circuit for
current to flow (out of the end of the battery,
through the wires and components, then back into
the end of the battery) just as one needs a
closed network of pipes for a plumbing system to
be able to circulate water from the pump, through
the pipes, then back to the pump again.
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Components can be placed in series (i.e. one
after another) so that electrical current must
pass through them one after another before
returning to the battery. Components in series
have the same electrical current passing through
them.
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On the other hand, components can be placed in
parallel (i.e. one beside another) so that the
electrical current must chose which one component
to pass through, bypassing the others.
Components in parallel have the same voltage drop
but usually carry different amounts of current,
with more current flowing through the easiest
path (i.e. the path with the least resistance).
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In terms of (water) plumbing, a water heater
would be in series with a room hot-water radiator
the water flows through the water heater then
the exact same water molecules go on to the
radiator. On the other hand, two hot-water room
radiators might be plumbed in parallel the
water would choose to go either to the living
room radiator or to the bedroom radiator before
returning to the water heater, but no single
water molecule would go through both radiators in
1 trip.
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Components and vocabulary
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Battery pushes on the electrical charges
(though none will actually flow if the circuit
isnt complete) the battery has two terminals
labeled positive () and negative (-) the most
negative voltage region in the circuit, often the
negative end of the battery, is sometimes called
ground or 0 volts the amount of push the
battery supplies is the battery voltage, often
1.5 V or 9 V or 12 V (with respect to ground)
as a battery gets worn out (or if it gets too
cold!) its voltage will go down until the battery
is too weak to continue to push current through
the circuit
symbol
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Wire provides a path through which electrical
current can flow ideally a wire has no
resistance
symbol
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Resistor serves as a current path but limits
the amount of electrical current flow and reduces
the pressure (i.e. drops the voltage)
resistance is measured in Ohms (?) for
resistors it doesnt matter which way and are
connected when current flows through a resistor
the resistor may get hot (i.e. it dissipates
energy), so resistors can also be used as heaters
symbol
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Switch place where a current path can be
mechanically opened and closed, to start or stop
the flow of electrical current switches are
used to turn things ON and OFF place the switch
in series with the component(s) it is meant to
control, like a battery
symbol
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Capacitor serves as a place to temporarily
store electrical charge, like a temporary battery
charge it up (store electrical charge) then
discharge it (temporarily produce electrical
current) capacitance is measured in Farads (F)
electrolytic capacitors are ones in which it
matters which way and are connected
symbol
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Diode serves as a one-way valve, only allowing
current to flow one direction under normal
circumstances an LED (light emitting diode) is
a diode (often red or green) that glows when
current flows through it diodes must be
inserted the right way around for the circuit to
operate correctly
symbols
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Voltage regulator a chip that can be powered by
a range of voltages but uses internal circuitry
to drop the voltage to output a very stable
voltage (e.g. a 5 V regulator might be able to
able to be able to run off any voltage from 6 V
up to 20 V, but it always outputs exactly 5 V)
this is handy for providing a constant voltage to
components even when dealing with batteries that
can vary in voltage and circuits that can vary in
overall resistance
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IC (Integrated Circuit, AKA chip) a silicon
chip with many tiny transistors on-board which
can be programmed to make decisions (a
microprocessor chip), to store digital
information (a memory chip), to convert digital
input to analog form (DAC), or vise versa (ADC),
etc. connects to other components through its
multiple legs, called pins be very careful
never to put a chip in backward!
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ADC (Analog to Digital Converter) a chip that
takes analog (continuous) voltage input, perhaps
from a sensor, and converts it to digital form
for ease of use
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Breadboard a board into which components can be
plugged and unplugged, allowing one to build and
check circuits without having to be as permanent
as soldering them together
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PCB (Printed Circuit Board) insulating board
onto which components can be soldered, with
metallic traces etched into the board to make
electrical connections without having to use
external wires
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Perf. Board (Perforated (Circuit) Board)
insulating board onto which components can be
soldered, with no metallic traces etched between
holes like on a PCB using perf. board is more
permanent than using a breadboard but you need to
connect components with external wires
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Transistor 3-leg device used in logic circuits
so that a small/weak electrical current at one
point can control a much larger/more-powerful
electrical current elsewhere in the circuit
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Sensor a device, often powered using 5 V and
ground (0 V) connections, that has a third
output the voltage of which varies predictably
and reproducibly as some physical parameter
changes like temperature or air pressure needs
to be calibrated (i.e. the output needs to be
checked using known physical conditions) so
output values can be correctly interpreted
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Socket a dummy set of receptacles that matches
the pins on a chip the socket is soldered onto
the board and the chip snaps into it so that the
chip can be replaced (carefully!) without
resoldering if it goes bad
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Cable a wire or set of parallel wires
connecting components together for example,
sensors often use a 3-wire cable with the wires
used for 5 V, ground (0 V), and signal (output
voltage)
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Battery pack a device for holding multiple
(identical) batteries, either in series ( of one
battery attached to the of the next, in which
case the total voltage is the sum of the battery
voltages) or in parallel (all terminals
connected together, all terminals connected
together, in which case the battery pack has the
same voltage as each individual battery, but it
will last longer (i.e. can provide current for a
longer amount of time))
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Audio jack used to make a pull-before-flight
pin to start a flight computer just before we let
go without having to open up a payload box
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Male and female headers used to allow quick
electrical connections between sensors, flight
computers, for programming, etc.
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Shrink wrap plastic insulation tubing one can
slide over exposed metal, like a solder joint, to
insulate it electrically from nearby wires
shrink wrap contracts (shrinks!) when heated with
a heat gun think ahead you might need to put
the shrink wrap on before you do the soldering
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Using a multimeterto make resistance andvoltage
measurements
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Multimeter a device with two probes (red
(positive) and black (negative)) with which one
can make resistance, voltage, and current
measurements for resistance and voltage
measurements (all well be doing in this class)
always plug the black probe into the socket
labeled COM and the red probe into the socket
labeled V ? mA
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Measuring resistance in Ohms (?). Turn the dial
to a value on the Ohms scale larger than the
resistance you expect. Touch the two probes to
either end of the resistor (preferably when it is
not part of any circuit, lest there be alternate
current paths around the resistor). Adjust the
dial downwards as necessary. Read the value of
the resistance in Ohms, kiloOhms, or MegaOhms.
(Note you can also read off resistance values
by using resistor color codes.)
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Measuring DC voltage (i.e. battery-type voltage).
Turn the dial to a value on the DC Volts scale
larger than the voltage you expect. Touch the
two probes to the two points on the circuit
between which you want to know the voltage
change, trying to put the black probe on the
point with the lower voltage (i.e. closer to
ground). Adjust the dial downwards as
necessary and read off the value in volts.
Notice that the reading is the voltage drop from
the red (positive) probe to the black (negative)
probe, so a positive reading means that the red
probe is indeed at a more positive voltage than
the black probe. On the other hand, a negative
reading means the red probe is more negative than
the black probe. (See next slide for photos of a
voltage reading being made.)
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Using a multimeter to measure the voltage of a
battery. Notice that the red probe goes to the
terminal and the black probe goes to the
terminal to get a positive value on the screen.
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Comments on someactual circuits
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The circuit diagram forthe heater circuit3
batteries in parallel (so they last longer)3
resistors in series (which will get hot)1 switch
(to turn it ON and OFF)
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Sensor for theweather station1 pressure gauge
(0 to 15 psi)1 temperature gauge4-wire cable
5V, ground, press. output, temp. output
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Animation of a 555 timer chip circuit,similar to
the one we built. http//courses.ncsu.edu8020/ece
480/common/htdocs/480_555.htm