# Engineers in Training Day 2 Developed by Shodor and Michael Woody.

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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.

 Breadboards 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?

 When we come back we’ll look at some more electronic components and build a more complex circuit

 Go to http://falstad.com/circuit/http://falstad.com/circuit/  Choose Circuits → Basic → Ohm’s Law  Ohms Law: V= I x R or I = V/R  In 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/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?

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