Download Electricity and Circuits

Engineers in Training
Day 2
Developed by Shodor
and Michael Woody
 What


uses electricity?
Name some things that use electricity
Try to name something you like to do that
doesn’t use electricity.
 Everything
that uses electricity is made up of
at least one circuit
 To figure out how we use electricity we first
will look at water.
 Suppose
we want to grind some grain using a
water wheel
 What do you need to have a water wheel?





Water
Hill (for the water to flow down)
Pipes/channels (to direct the water)
The water wheel (to power something)
Mill, pump, etc (something needing power)
 What
things might we measure about our
water wheel setup?
 How
high/steep is the hill?
 How
fast is the water moving?
 How
much grain can we grind every day?
 Our
circuits are very similar to waterwheels.

Instead of a landscape we have a breadboard

This is where we put our circuit together
 Our
circuits are very similar to waterwheels.

We have electric charge instead of water

This is what makes everything go in the circuit
 Our
circuits are very similar to waterwheels.

And a battery instead of a hill

Without this the charges wouldn’t move, they
would just stand still and do nothing.
 Our
circuits are very similar to waterwheels.

Wires for pipes and channels

These carry the electricity to where we want to
go and direct it
 Our
circuits are very similar to waterwheels.

A light bulb (or motor, etc.) that needs power
instead of the water wheel.

This is the end goal of our circuit, to accomplish
some task.
 Voltage




(potential)
This is like the height of our hill
The more voltage, the more the electricity wants
to move
We measure this in Volts (V)
High voltage means more electricity (charge) will
go through a wire
 Current




(rate of flow)
This is like amount of water flowing
Current measures how much electricity is moving
through a wire
This is measured in Amperes or Amps (A)
High current means a lot of electricity is moving
(high current is very dangerous)
 Power





This is how much work our circuit does
Corresponds to how much grain is milled, etc.
Measured in Watts (W)
High Power = lots of work which can mean heat.
100 W light bulb is hotter and brighter than 60W.
 We
are going to build a
circuit together now.
 We
will use the battery,
the breadboard, the
resistor, and the LED to
make the LED turn on.
9Volt
Battery
10 kΩ
 Breadboards
Seperate
Node
Connected
One Node
Not
Connected
are
used to connect
things quickly
 You can proto-type
circuits quickly
 This
diagram shows what holes are
connected to each other.
 You connect things together by plugging
them in to holes connected to each other
 Battery
 Source
of constant potential (9 V)
 Wires
 We
have wires connected to our battery.
+ lead (red wire) – outflow from high potential
- lead (black wire) – inflow to low potential
 Light
Emitting Diode (LED)
 Emits light when current
flows through it
 Current can only flow in
one direction, from + to (like a water wheel that
won’t go in reverse)
Long lead (+)
 Short lead (-)

 Can
be damaged by high
current



Resistor
Will keep our LED from getting
damaged by too much current.
New term:
Resistance – how easy is it for current to
flow
 Symbol (R)
 Unit (Ohm – Ω)


Circuit element
Resistor, like a wire
 Regulates the flow of current
 The higher the resistance the less
current will flow
 Current = Voltage/Resistance

 Use
the battery, the
breadboard, the
resistor, and the LED to
make the LED turn on.
 Follow the “LED Circuit”
in your handout.
 Watch for polarity (plus
minus signs) especially
for the LED
 Why is the resistor
necessary?
9Volt
Battery
10 kΩ
 When
we come back
we’ll look at some
more electronic
components and
build a more complex
circuit
 Go
to http://falstad.com/circuit/
 Choose
 Ohms
 In
Circuits → Basic → Ohm’s Law
Law: V= I x R
or
I = V/R
which branch will more current flow?
 Imagine
a networks of pipes
Like a glass that holds water
 The more electricity flows in, the higher the voltage
(water level)
 It will eventually ‘fill up’ with electricity
 A large capacitor is like a wide glass



Needs more water (electricity) to get to the same height
(voltage)
For same voltage and resistance of the circuit, it will take longer
to fill all the way up
Used to oscillate between a high (+5V) and low (0V)
voltage
 Stays high until the Threshold input rises above a
certain level, then switches low and lets the
attached capacitor start to discharge.
 Stays low until Trigger falls below another level,
then switches high and stops the capacitor from
discharging.

 Go
to http://falstad.com/circuit/
 Choose
Circuits → 555 Timer Chip → Square
Wave Generator
 Build
the circuit shown
 Use
the output to power the LED Circuit from
first exercise
 “555
Timer Circuit” in your handout gives the
circuit, for convenience
 The
555 timer will
switch the output
back and forth as
the capacitor
charges and
discharges.
 Before trying both
capacitors, which
one will make the
light blink faster?
9 Volt Battery + lead
or
5.1 Volt Regulator Output
10 kΩ
555
Timer
GND
VCC
TRIG
DIS
OUT THRSH
RESET CTRL
10 kΩ
555
Timer
Output
10 kΩ