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 Switches

- Used for calculators,
mobiles etc where many
switches need to be placed
next to each other.

(momentary / non-latching)

 

S.P.S.T Switches

These we have come across already. S.P.S.T. stands for
"single pole single throw". They have two connections and
can either allow current to flow or not to 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 is useful for detecting moving objects like
wheels when you need to find their speed.

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" and 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. Quite often it is placed near
the safety guards of dangerous machines to tell you if the
guard hasn't been put into position. They can be wired to
prevent a 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 twice 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 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 sound.
Now select from the list below the
name and best description
of the switch that
could be used:

Rocker - Tilt - Membrane - Micro - normally open -
normally closed

 

 

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