Elwctronica and mechanical systems Flashcards
what are mechanical systems made up of
individual physical parts which each have a particular function in the system
motor vehicles components
- steels often used for vehicle parts as its strong, easy to work with and malleable
- car bodies made from steel as its tough, in an accident it’s designed to crumple
- aluminium is a more corrosion resistant alternative to steel for car body parts
- strips of electrically conductive material on the inside of a cars rear window can be used to defog it
- engine electronics are made from materials that can cope with very high and low temperatures
why is aluminium better than using steel in motor vehicles
Aluminium is more corrosion resistant
Aluminium is less dense (lighter) so improves performance
- but expensive and hard to work with
domestic appliances components
- washing machines use a drive belt, often made from rubber, as its strong and flexibe, so can resist pulling forces without breaking
- the spinning drum and any pumps must be resistant to water during use so stainless steel or plastic is often used
- heating elements are often made of nickel-chromium alloy which has a high melting point so it can get hot without melting
what are photosensitive materials
materials that respond to being exposed to light
examples of photosensitive material
- when making PCBs, a process called photo etching is used to transfer the design of the circuit onto the board
how does aluminium protect itself from corrosion
- naturally react with oxygen to form a layer aluminium oxide on exposed surfaces
- this is a hard material that sticks strongly to the fresh aluminium beneath, protecting it from further corrosion
whats is anodisarion
a process that thickens the protective oxide layer that is already present, using an electric current. in aluminium this makes the surface harder
- used in aircraft parts, pans, window frames
how should electrical components be bought
to match a chosen power supply
what are e12 resistors
ones that have a constant resistance
what are e12 resistors tolerance
plus or minus 10 percent
what are coloured bands used to do
identify resistors
how many coloured bands are there on e12 resistors
4
what do the bands on e12 resistors do
band 1 and 2 - represent the first two digits of the value of resistance
band 3 represents the number of zeros that come after the first two digits of the value of resistance
band 4 represents the tolerance- its always silver for e12 resistors
ways ICs are packaged
using DIL’s (dual in line package)
describe DILS
- the circuit itself is placed into a rectangular protective case made of plastic or ceramic
- metal pins stick out of the casing in two parallel rows.
- the pins connect the IC to the rest of the circuit
- each pin has a number, a dot or a notch on the casing to show where the first pin is
what is a common type of microcontroller
a PIC
how are pics often sold
- in DILS and have a voltage rating of between 3 and 5.5V
some PICs are OTP microcontrollers, what does this mean?
they are one time programmable, can only be programmed once
what are advantages of PICs having flash memory
they can be reprogrammed up to 100,000 times so can be used again and again
features of chains
- they transfer rotary motion from one sprocket to another
- they are sold by width and pitch
- they come in standard lengths
features of gears
- come in variety of widths
- can also have different numbers of teeth, to change the speed of rotation
- different types of gear will have different tooth shapes, eg bevel gears have teeth angled at 45 degrees
features of springs
2 major types - compression springs which resist compression, and extension springs which resist extension
- have different lengths widths and number of coils - which can affect the spring rate of the spring
features of laser cutters
- uses a laser to cut out material
- machine cuts by following a design thats loaded into it, this instructs it where to cut the material
- laser cutters use designs made by CAD
- they can only cut in 2d, so have to be sheets of material
examples of materials laser cutters can cut
plastic
wood
cardboard
fabric
some metals
pros and cons of using a laser cutter
pros
- has a huge range of uses and can be used to cut out a variety of mechanical components such as PCBS
- high precision and accuracy
cons
- requires a lot of power so is expensive to run
what do PCB drills do
drill circuit boards so that pins or wires of each component can be pushed through the holes and soldered
features of soldering
- uses solder to attach components in a circuit. its used to hold components is place and connect a components metal pins to wires or copper tracks
- usually a ton based alloy, can be applied manually by melting it with a hot soldering iron
- electrically conductive, so it’s used as an electrical connection between the components and the rest of the circuit
describe flow soldering
- components are placed onto the PCB, which is then passed over a pan of molten solder
- a pump produces an upwelling at the right height to just touch the base of the board and solder each component in place
- the whole process is quick and cheap, but it takes a lot of thought and is only used for components with pins that poke through
describe the process of photo etching
- the layer of the copper tracks of the PCB is designed using a CAD software, this is printed onto a sheet of transparent material to form a PCB mask
- The mask is placed onto the blank PCB on top of the photosensitive layer
- the board is exposed to UV for 3 to 10 minutes. the mask is opaque in some areas, but the rest of the mask is transparent, so UV can travel through the photosensitive layer
- the board is then exposed to two different chemicals separately
- copper still covered by the photosensitive layer isnt removed from the board becomes copper tracks
- any remaining photosensitive layer is stripped off,exposing the bare copper tracks. now the board is ready for components to be added
What is pick and place assembly?
The process of placing components onto a PCB in the correct position and orientation so they can be soldered onto the board
- Can be done using a pic and place cam machine or by hand
features of pick and place machines?
-use suction cups to pick up components and move them to the correct location
- quick
- expensive
features of manual assembly
- using tweezers to increase precision of placement of components
- usually used for components with pins that need to be pushed through holes, as machines cant do this very easily
- take longer than machine assembly and more likely to include more mistakes due to human error
features of a PCB lacquer
- a surface treatment for PCBs
- thin polymer film that provides a protective barrier against moisture, chemicals, large temperature change and dust
- helps electronic components deal with harsh environments to help decrease corrosion
- they can be sprayed on, painted, or applied by dipping the whole board into the lacquer
- many are fluorescent and glow in UV light, makes it easier too see
features of lubricants
- reduce friction between moving parts as it can reduce efficiency and lead to interlocking parts being worn down
- used in bike chains,
- examples of lubricants include - graphite, oil, silicone, grease
