The document discusses relay pin configuration and implementation. It describes how a relay works as an electromagnetic switch with common, normally closed, and normally open terminals. When a coil is energized with DC voltage, it creates a magnetic field that attracts a connector pin and switches the connection from the normally closed to the normally open terminal. The document then provides an example of how to use two relays to control the direction of a DC motor connected to one power source by switching the polarity. Pushing one button energizes the relays in one configuration to run the motor in one direction, while pushing the other button energizes the relays in the opposite configuration to run the motor in the reverse direction.

1. Relay Pin Configuration and
Implementation
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2. Relay is frequently used by engineers and
technician wherever a smart system is required in
terms of the breaking or connecting a circuit or to
introduce some automation. Relay is an
electromagnetic switch that is used as a two way
connector or switch in the robotic circuit at low
voltage level from 12V to 30V and also they are
used in the power system (transmission and
distribution) at high voltage level of order in KV.
But here I am goanna to talk about the relay
those are used in the robotics circuit to control the
motor drive circuit and sensor.
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3.  Internal structure and construction of a
relay is shown in the picture below
showing the various terminals of the relay
i.e. common, normally closed (NC),
normally opened (NO), coil terminal C1 &
C2 , connector pin and coil used inside
the relay.
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5.  Connector pin (made up of magnetic material) is fixed
at one end as the one terminal called the common
terminal whereas two terminal NC and NO are at the
opposite end to the common terminal. Coil in the relay
has resistance of 1K and is energised with the dc
voltage, thereby produces the magnetic field. Normally
(without the excitation of coil) connector pin is
connected to the upper strip which is the portion of the
right terminal and hence termed as normally closed
(NC). Whenever coil is excited, as a result of flow of
current in the coil magnetic field is produced which
attracts the connector pin towards itself and thereby
shifts the connector pin from NC to NO.
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6. Schematic diagrams show the
function of excitation above. Thus
relay act as a two way switch
which makes the connection
between common terminal and
NO terminal in excitation mode
and disable the connection in
non-excitation mode.
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7. Let’s implement the relay to run the
DC motor in either direction with
one power source.
 When a DC motor is connected to the DC power source
then due to unidirectional nature of current it runs only in
one direction either clock wise or counter clock wise. If it
is required to run in another direction then polarity of the
battery is needed to revert so that polarity of current also
changes. But polarity of current can be changed
without reverting the battery using a two way switch.
And it is better accompanied by the relay.
 Circuit Description: Here is the requirement of one DC
Motor, two relay, two push key, one power source to run
motor (let 9V) and one 5V battery to energise the coil.
Make the connections as depicted in the diagram
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9.  Two relay are being used here so the two terminals
of both the relay are connected in such a way so
that after connection both the coil appears in
parallel, here this is necessary because excitation of
both the relay must occur simultaneously. Excitation
of coils may be with external power source or within
the same power source which is being used to
power up the motor with the help of voltage
regulator.
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10.  After making the connections now you will be able to control
the direction of motor with two push key S1 &S2. Whenever
you press the S1 then motor is connected to the two different
terminals of the battery and thus motor runs in one direction.
But when S2 is pressed then excitation of two coils occur and
connector pin of the relay is shifted from NC to NO terminal
and connects the motor to battery in the reverse polarity than
that of previously connected and motor runs in the opposite
direction.
 Note: Direction of current or polarity across the coil does not
matter for the excitation.
 Same circuit is implemented to control the direction of two or
four motors by adding two more relay in the same manner
where no readymade remote control is being used.
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