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 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?