Electricity and Circuits

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Electricity and Circuits

• Engineers in Training
• Day 2

Developed by Shodor and Michael Woody
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Electricity

• What uses electricity?
• Name some things that use electricity
• Try to name something you like to do that doesnt
  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.

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Waterwheel

• 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)

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Waterwheel
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Three Important Measures

• 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?

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What about Circuits?

• Our circuits are very similar to waterwheels.
• Instead of a landscape we have a breadboard
• This is where we put our circuit together

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What about Circuits?

• Our circuits are very similar to waterwheels.
• We have electric charge instead of water
• This is what makes everything go in the circuit

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What about Circuits?

• Our circuits are very similar to waterwheels.
• And a battery instead of a hill
• Without this the charges wouldnt move, they
  would just stand still and do nothing.

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What about Circuits?

• 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

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What about Circuits?

• 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.

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Terminology

• 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

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Terminology

• 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)

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Terminology

• 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.

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Lets Build a Circuit

• 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.

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Breadboard

• Breadboards are used to connect things quickly
• You can proto-type circuits quickly

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How to use your Breadboard

• This diagram shows what holes are connected to
  each other.
• You connect things together by plugging them in
  to holes connected to each other

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Parts of Our Circuit

• Battery
• Source of constant potential (9 V)

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Parts of Our Circuit

• Wires
• We have wires connected to our battery.
• lead (red wire) outflow from high potential
• - lead (black wire) inflow to low potential

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Parts of Our Circuit

• 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 wont go in reverse)
• Long lead ()
• Short lead (-)
• Can be damaged by high current

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Parts of Our Circuit

• 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 O)
• Circuit element
• Resistor, like a wire
• Regulates the flow of current
• The higher the resistance the less current will
  flow
• Current Voltage/Resistance

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Lets Build a Circuit

• 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?

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Take a Break

• When we come back well look at some more
  electronic components and build a more complex
  circuit

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Exercise

• Go to http//falstad.com/circuit/
• Choose Circuits ? Basic ? Ohms Law
• Ohms Law V I x R or I V/R
• In which branch will more current flow?
• Imagine a networks of pipes

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Capacitor

• 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

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555 Timer Chip

• 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.

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Exercise

• 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

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The Circuit

• 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?