Switches - Taking Control 

 

We have seen in the last section how switches give us
control. They are used to interrupt the current flowing in a
circuit. There are many different types of switch and in this
section we will look at some of them and describe how they
work.

There are different switches for different situations. They
have to be chosen carefully to suit the user and environment
they are in.
Please go down the page to view some of the
different types we commonly use.

 

Rocker Switch

- Quick and easy to operate

- Used for room lighting

- Once operated they stay in the   position they have been put.
  (latched)

 

Push Button Keyboard
Switches

- Easy and comfortable to use.

- Used in standard keyboards
  for P.C's.

- Once operated they return.

- Momentary /Non-latching

 

Membrane Panel Switch

- Waterproof, hygienic and
  safe to use in damp areas.

- Used for cookers,vending
  machines

- Photocopiers or for flat
  surfaces.

- Momentary /Non-latching

 

Push Button Membrane Switches

- Used in oder calculators and
  mobiles.
- Useful when many switches   need to be placed close   together.

- Momentary / Non-latching

 

S.P.S.T Switches 

We have come across these already. S.P.S.T. stands for
"Single Pole Single Throw". They have two connections and
can either allow current to flow, or not flow, in the circuit it
has been placed.


Now open the link above to "Components and Symbols"
and read about the six different types of switch shown
in its table. Then fill in the blanks below using the italic
words provided here.

large - push to make - red - push to break - reed - micro
- push - tilt

(To check your answers click outside the text boxes).

Q13, A switch will detect a magnetic field.
It can be used to help find the speed of a moving object - such as a rotating wheel.

Q14, A switch could be used in a circuit to
warn you if your bicycle was leaning over too much


Q15, Switches can either be normally closed or
normally open before they are operated.
A switch, which is normally closed, could be
used to make a light turn on when you take your hand
off it.

 

 

S.P.D.T Switches 

S.P.D.T. stands for "Single Pole Double Throw". A good
example of this type of switch is the micro switch. It has a
small sprung lever on the top which can be used to detect an
object or item pushing against it. Manufacturers can place them near the safety guards on dangerous machines to detect if the guard has been put into position. It can be wired to keep people safe, by preventing the machine from turning on.

 

Click on the micro switch lever to operate it.

Before it has been pressed, the switch contact on the left
(known as the pole) is normally conected to the top
connection as shown.

After it has been pressed the contact on the left now swaps
over and connects to the bottom connection on the right.
When you let go it springs back to its previous position - this
is another example of a momentary or non-latching switch).

Latching switches

A rocker or toggle switch doesn't usually spring back after
you remove your finger from the button. It requires a second
touch to return - this is known as a latching switch and is
therefore useful as an on/off button on electronic products.

Click the latching switch down and up to see how the current is redirected.


Current flow inside

an S.P.D.T. switch

 

 

Q16, Read the following description of an intruder
alarm:

Point at the door
to close it

A simple alarm circuit, with battery and buzzer,
is turned on and off by a lever operated switch (see
diagram above). When the door is closed it pushes
firmly against the switch and the buzzer is off. When
an intruder opens the door, the switch "makes" & the
buzzer sounds.
Select from the list below, both the
name and the best technical description of the switch
that could be used:-

rocker - tilt - membrane - micro - normally open
- normally closed

 

 

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