EP Revision Flashcards
Lamp or bulb
Push to make switch
The current can flow only when the switch is pressed.
The button part is often (but not always) red
NOT gate
Double Pole Double Throw
Poles are the number of switches inside the main switch. Throws are the number of outputs the switch has.
You can tell the number of these by looking at the number of pins or legs the switch has.
The toggle switch below is a double pole double throw (DPST) since it has 6 connections..
These are the most common switches you will see because by using some or all of the connections you can make the switch act like any of the other types.
AND gate
Voltmeter
Ammeter
HIGH IMPACT POLYSTYRENE
High Impact Polystyrene Sheet (HIPS) is available in various thicknesses and colours (mostly opaque).
It is waterproof, self coloured (no need to paint), does not conduct electricity and can be heated until it is soft and then have it’s shape changed (called thermoplastic or thermoforming)
Commonly used with a mould in vacuum forming and can be glued (with solvent cement) or even welded together (industrial process really)
Latching switches
All of these stay in one position until deliberately changed. They do not spring back when let go. They can all use this symbol.
Micro switch
These switches are different because they are not operated by a persons finger, but usually part of a machine or piece of equipment.
They can have buttons, levers or rollers and are used to detect when a fridge door is closed, a machine has a guard in place, or when part of a machine has reached the end of it’s movement.
Light emitting diode (LED)
Motor
ALUMINIUM
Lightweight, non-rusting, good conductor of heat and electricity, expensive but can be melted down and reused quite straightforwardly (with a big factory and furnaces… - NOT “easy”)
Can be machined (using computer controlled machines - CNC), cast (heated to a liquid and poured into moulds) or, in sheet form, bent into boxes
Pure aluminium is quite soft for a metal and so is often mixed or alloyed with other metals to improve it’s properties.
Single Pole Single Throw
Poles are the number of switches inside the main switch. Throws are the number of outputs the switch has.
You can tell the number of these by looking at the number of pins or legs the switch has.
The rocker switch below is a single pole single throw (SPST) since it only has 2 connections.
You can find more information here(right click and ‘open in new tab’ to not lose your progress here)
Exclusive OR gate (XOR or EOR)
Electrolytic or polarised capacitor
Buzzer
Toggle switches
Theses are often (but not always) used as ON/OFF switches and are sometimes marked with these labels
They usually mount through a hole drilled into the material they are used in and fastened with a nut on the front.
They can be SPDT or DPDT (and sometimes other forms as well)
NOR gate
Loudspeaker
ACRYLIC
Acrylic (also known as Perspex) is a ‘thermoplastic’ – it will go soft when you heat it and you can change it’s shape. It can be bent on a line bender or injection moulded. It also laser cuts well.
It is waterproof, self coloured (no need to paint), does not conduct electricity and is available in different thicknesses as well as lots of opaque and translucent colours and also clear.
It is quite strong (for a plastic) and is hard but may shatter if a large force is applied. It can be used for cases for circuits or as covers for displays where it can protect them
Thyristor
Diode
Resistor
Push to break switch
The current only flows when the switch is not pressed - pressing the switch stops the current.
If it is a push switch the button is often (but not always) black
OR gate
Relay
PINE
Softwood (needles rather than leaves), fast growing (about 35 years), needs protecting (paint or varnish), OK rather than beautiful, easy to cut and glue into boxes, sustainable (trees are cut down and then replaced and grown in large plantations around the world - Scandinavia is a big, close by, producer), narrow trunks and very thin (useless) branches mean methods must be used to join them together to make bigger boards (like in IKEA furniture)
BRASS
Alloy (mixture) of copper and zinc.
Strong, rust proof, machines and recycles well, conducts heat and electricity well,
Used a lot before stainless steel became common (door knobs etc) but used a lot today for electrical connections inside plugs, battery compartments etc
Single Pole Double Throw
Poles are the number of switches inside the main switch. Throws are the number of outputs the switch has.
You can tell the number of these by looking at the number of pins or legs the switch has.
The slide switch below is a single pole double throw (SPDT) since it has 3 connections.
Momentary switches
All of these allow current to flow when pressed but it stops as soon as they are released - they do not ‘stay on’
They can all use the ‘push to make’symbol
Reed switch
These are momentary switches activated by a magnet .
If there is a magnet close by the switch conducts, but if there is no magnet then the switch stops conducting.
They are common switches and are frequently used in alarm circuits where they might be packaged in plastic to protect the glass tube
COPPER
Very good conductor of electricity (and heat) and is ductile - it can be stretched out into long thin wires without breaking.
Most common use for us is in wires and cables (covered with plastic to stop it touching other wires and to help identify a particular wire)
Also used for the tracks on PCBs.
Doesn’t rust and recycles well but is expensive
Light dependent resistor (LDR)
Variable resistor
Battery
MDF
Medium Density Fibreboard (softwood trees ground into fine dust, mixed with glue and them rolled into very wide, thin sheets of different thicknesses).
Large sheets mean large objects can be made easily. Consistent quality, thickness, weight etc. Cuts and glues well
Sustainable as all of tree is used and new trees can be planted that can be harvested after 25 years (less than full trees)
Needs covering to protect and improve appearance - paint or thin covering of another wood (veneer) or a laminate such as formica used in kitchen tops or doors
Capacitor
Transistor
NAND gate
MILD STEEL
Strong and one of the cheaper metals
Magnetic, conducts electricity (but see below) and heat and can be delivered in flat, round or pre-shaped pieces.
It is heavy and rusts in the presence of oxygen, which gets worse in wet or damp conditions. It will need to be protected, commonly by painting. Rusting can prevent an electrical connection from being made (use copper or brass if this is likely)
Switch
Thermistor
LIGHT DEPENDENT RESISTOR
…or LDR
A resistor whose value depends on how light or dark it is
In the dark it is a big resistor
THERMISTOR
A resistor whose value depends on how hot or cold it is.
It is a big resistor when it is cold.
MOISTURE SENSOR
These can be thought of as a type of resistor.
When they are dry they have a very big resistance but when they are wet it drops a little (but is still quite big!)
There are two main types.
One type has two ‘probes’ and is often put into plant pots as part of a system to water them - when the soil is dry they have a very big resistance and when the soil is moist the resistance is lower.
The other sort has two PCB tracks that interlock but don’t touch. When it is dry it has a very high resistance but of a drop of water lands on it and joins the tracks the resistance gets lower. These are often used as rain sensors.
Both types can be made in school and there is no symbol.
PIEZO ELECTRIC SENSOR
Piezo electric materials produce a very small voltage when a force is exerted on them.
They are used on phones to detect when the ‘home’ or ‘back’ buttons are pressed but can also be used in alarms to detect if a door is being hit or pushed by a burglar.
