Electricity
Electricity
How We Approach Electricity
 Electricity can be beautifully described with physics and mathematics
 However, we will focus on building an intuitive understanding and applying principles to build devices
 There will be some basic math, but that is not our focus
 Rules of Thumbs
Electricity Analogies
Common Analogy

Electricity can be thought of as water flowing down a pipe

The higher the water falls from, the greater the pressure

More water can flow (and flow faster) through a larger and smoother pipe

Water can be stored in a container (like a battery)
Common Analogy
 The “pressure” (or height) of the water is the voltage
 Measured in units called volts (V)
 Higher voltage means more potential energy
 Our circuits will typically consider voltages 0v  5v
Common Analogy
 The “rate of flow” of the electricity is the current
 Measured in units called amperes or amps (A)
 Higher amperage means electrons are flowing faster
 In equations, current with be denoted with the letter I
 Note: 1 A is a lot! Our projects will consider smaller values such as 0.2 A.
 Instead, we will say 0.2 A is 200 milliamps (mA)
Compare
Consider two straws. Which has greater flow?
Resisting the Flow
 The narrower pipes restrict or resist the flow of water
 The measure of how well something resist or allows electricity is resistance
 Measured in units called Ohms (Ω)
 More Ohms means more resistance, which means less current (flow)
Resistors
 Resistors conduct electricity, but are used to restrict / slow the flow of current
 They can be connected either direction
 We measure values from 0Ω to 10,000Ω
 10,000 Ohms is 10 kiloOhms (10 KΩ)
Accessibility Note
 Resistor values are determined visually by color bands
 Unfortunately resistor labeling is not accessibly designed
 To support students who are color blind or have difficulty distinguishing colors, here are resources for support
Key Concepts
 Electrons are negativelycharged particles
 Electricity is the flow of electrons from positive to **negative **(flow of energy)
 Electronics is the study of devices that control / interact with the flow of electricity
Circuits
 Electricity will only flow if there is a circuit
 A circuit is a complete loop from a positive voltage source to a negative (lesser) source, through a conductive material
Voltage as Difference
 When we describe voltage, we are measuring the difference between two points
 In the water analogy, water could fall from 500 ft to 400 ft, or from 100 ft to 0 ft
 In both cases, water fell a difference of 100 ft, but the reference point changed

In a circuit, we commonly call the reference point Ground (GND) and say it is 0V
 In homes and buildings, ground is literally connected to the earth
Voltage Source
 In our circuits, we will use a voltage source to provide energy potential
 USB power: 5v (also stepped down to 3.3v which the Photon 2 uses)
 9V battery: 9v
 Rechargeable lithium battery: 3.7v
 Our circuits will have a positive voltage (e.g. 3.3v or 5v) and ground voltage (0v)
 We will consider that current flows from the positive part of the circuit to the negative
Ohm’s Law
 There are only a couple electrical laws that we need to know
 There is a relationship between voltage (V), current (I), and resistance (R)
V = I * R
or Voltage = Current * Resistance
 Rule of thumb: As resistance increases, the current decreases
Example
1.) The voltage source is 9v. If we have a resistor that is 300 Ohms, what is the current? 2) The voltage source is 9v and you want to provide a current of 9mA. What size resistor should we use?
Building our Circuits on Breadboard
 We will use breadboards to connect our circuits
 The power rails (on the long ends of the board) are all connected together
 On the interior, each group of 5 pins are connected
Inside a Breadboard
 Breadboards are built with rows and columns of connected pin sockets
 Underneath each row and column are strips of metal that form electrical connections
Breadboard Connections
Breadboard Connections
Important Note
 Different size breadboards are mostly identical, but note that the power rails are not connected the entire length of the board
Credits
 Mabacam Flickr via Compfight cc
 PickComfort Flickr via Compfight cc
 verchmarco Flickr via Compfight cc
 Craig Walkowicz Flickr via Compfight cc
 Images created with Fritzing