Engineers in Training

Day 2

Developed by Shodor and Michael Woody

What uses electricity?Name some things that use electricityTry 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?WaterHill (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 hillThe more voltage, the more the electricity

wants to moveWe 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 flowingCurrent measures how much electricity is

moving through a wireThis is measured in Amperes or Amps (A)High current means a lot of electricity is

moving (high current is very dangerous)

PowerThis is how much work our circuit doesCorresponds 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.

9VoltBattery

10 kΩ

One Node

Not Connected

ConnectedSeperate Node

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?

9VoltBattery

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 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/

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 + leador

5.1 Volt Regulator Output

OUT

RESET CTRL

VCC

DIS

THRSH

GND

TRIG

555 Timer

10 kΩ

10 kΩ

10 kΩ

555 Timer Output