Download Week 4 - Electronics

Loadall Challenge
Electricity and Switches
This week you will be:
• Learning about electricity and the definitions of
Voltage, Current and Resistance
• Learning about soldering, wiring and how to connect
a switch
• Building you Loadall’s electrical circuit
Electronics
• Electronics allow you to control things very precisely
• In this project you will use electronics to move the boom arm
backwards and forwards
• There are three main things we measure in electric circuits:
• Current (I)
• Voltage (V)
• Resistance (R)
Resistance (R)
Restricts flow of current
Voltage
Pushes
current around
circuit
Current (I)
Flows around the
circuit
Current (I)
• Current is a measure of how many charged particles (called
electrons) are flowing along a wire.
• The more electrons, the more current flowing.
• You can imagine the wire as a pipe and the current as the
amount of water that flows along the pipe.
• Amperes (A), known as “Amps” for short, are used to measure
current.
More Current
More water flowing
through the pipe.
Less Current
Less water flowing
through the pipe.
Voltage (V)
• Voltage is a measure of the
difference in charge between
two points on the circuit
The diagram below shows how water
pressure in a pipe is like voltage in a
battery
• Voltage tells you how much the
charged particles (electrons)
are being pushed around the
circuit
• Voltage is a bit like the pressure
in a pipe. The higher the
pressure, the more the water is
being pushed around the pipe
• Voltage is measured in Volts
(V)
More Voltage
Water in the pipe
is being ‘pushed’
more by the water
above.
Less Voltage
Water in the pipe
is being ‘pushed’
less by the water
above.
Resistance (R)
• Resistance is a measure of how difficult it is for current to flow.
• The harder it is for the current to flow the greater the resistance.
• You can imagine resistance like a pipe that becomes smaller.
The smaller pipe makes it harder for water to flow through it.
• Resistance is measured in Ohms (Ω).
• Components called resistors can be used in circuits to reduce
the amount of current flowing.
More Resistance
Harder for water to flow
Less Resistance
Easier for water to flow
Resistors
Can be used in
circuits to reduce
current flow
Ohm’s Law
These electrical variables are linked by Ohm’s Law.
• Ohm’s Law: 𝑉𝑜𝑙𝑡𝑎𝑔𝑒 = 𝐶𝑢𝑟𝑟𝑒𝑛𝑡 × 𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒
• Which is often written as: 𝑉 = 𝐼 × 𝑅
• This can be rearranged to show it in terms of current: 𝐼 =
• Or in terms of resistance: 𝑅 =
𝑉
𝐼
𝑉
𝑅
Circuits
• Below is a simple circuit diagram for a motor. The battery
provides power, the motor rotates and can be turned on/off by
the switch
• For the Loadall project we want to be able to change the
direction of the motor so that the boom arm can extend and
retract
• To reverse the direction that the motor spins in, you simply
Battery
wire theBattery
battery the other way around.
wired the
other way
round
Switch
M
M
Motor
spinning
clockwise
Motor
spinning anticlockwise
Switches
• The Loadall project uses a special switch that has three
positions:
• Extending (motor spinning in one direction)
• Retracting (motor spinning in the other direction)
• Off
• When you press the switch two wires in the circuit change
position
• Pressing this switch reverses the way the battery is wired.
This changes which way the motor spins.
Two wires
move when
switch is
pressed
Special switch
This three-way switch is
known as a doublethrow double-pole
switch.
Position 1
(e.g.
Extending)
Position 2
(e.g.
Retracting)
Switch positions
Each of the three switch states are shown below
Position 1
(e.g.
Extending)
Off
Position 2
(e.g.
Retracting)
Questions
1) Find the voltage (V) of a circuit with a current (I) of 0.06 amps
and a 200 ohm resistor (R).
2) A circuit consists of a 12V battery connected across a single
resistor. If the current in the circuit is 3A, calculate the size of
the resistor.
3) A circuit has a 12 ohm resistor and a 24 volt battery. Find the
current.
4) Find the resistance of a circuit that draws 0.2 amperes through
two 6 volt batteries.
5) A circuit with a 10Ω resistor has 0.9A current flowing through it.
Find the voltage of the battery.
6) The resistor in the same circuit is changed to a 50Ω resistor.
What is the current of the circuit now?
Answers
1) 12 V
V = I × R = 0.06 × 200 = 12 V
2) 4 Ω
R = V ÷ I = 12 ÷ 3 = 4 Ω
3) 2 A
I = V × R= 24 × 12 = 2 A
4) 60 Ω
R = V ÷ I = (2 × 6) ÷ 0.2 = 12 ÷ 0.2 = 60 Ω
5) 9 V
V = I × R = 0.9 × 10 = 9 V
6) 0.09 A
I = V ÷ R = 9 ÷ 50 = 0.18 A
The circuit diagram
used in this project
Soldering a Circuit
Soldering can be used to connect wires when creating your circuit:
1) First put the soldering iron in it’s stand and wait for it to heat up
2) While waiting cut the wires to length and strip the ends so that
bare metal is showing
3) Then position the bare wire against the terminal you want to join
it to
4) Next place the tip of the soldering iron against this point to heat
up the wire and the terminal
5) Using your free hand, feed the end of the solder onto the
connection point and wait for it to melt
6) Once the solder has melted remove the solder,
and then the soldering iron.
7) Hold the wire steady until the solder cools.
Recap
• Voltage, current and resistance are
the key things we measure in
circuits
• They are linked by Ohms Law: 𝑉 =
𝐼×𝑅
• By wiring a motor the other way
round you can change which way
round it spins
• The STEM project uses a special
type of switch (double-pole,
double-throw) so that you can
change which way round the motor
is wired
• This means you can make the
motor spin clockwise or anti-
Resistance (R)
Restricts flow of current
Voltage
Pushes
current
around
circuit
Current (I)
Flows around the
circuit
Practical – Wiring the Circuit
Use soldering to connect the wires to the switch
1) Connect a red wire (positive power) between
two opposite corners of the switch (as shown)
2) Connect a black wire to the other two corners
of the switch
3) Use a longer red wire to connect the battery to
the first switch terminal
4) Use a long black wire to connect the other side
of the battery to the second switch terminal
5) Connect two blue wires from the motor to the
two middle terminals of the switch
Switch wiring
diagram. Each of
the points 1-6 is
called a ‘terminal’