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In this CODESYS tutorial, we solve a classic PLC programming interview question: controlling 3 motors based on the number of active switches. This is a perfect example of combinational logic that every automation engineer should know.
The Logic Challenge: We have 3 Toggle Switches and 3 Motors.
If ANY 1 switch is ON → Motor 1 turns ON.
If ANY 2 switches are ON → Motor 2 turns ON.
If ALL 3 switches are ON → Motor 3 turns ON.
Codesys PLC Course:
https://www.youtube.com/playlist?list=PLI78ZBihrkE1Fbt1rtkzuMhoiM_RbjWUz
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0:00
[Music]
0:05
Hello everyone, welcome to automation
0:08
community. Today in this video we are
0:12
going to discuss an example in which we
0:14
will control three motors using three
0:17
toggle switches. So let's start.
0:22
PLC example three. We have three toggle
0:25
switches and three motors.
0:29
If any one toggle switch is on then
0:32
motor one will be on. If any two toggle
0:35
switches are on then motor two will be
0:38
on. If all the three switches are on
0:42
then motor three will be on. That means
0:46
if only one switch is on then motor one
0:50
will be on. That means if switch one is
0:52
on and other two switches are off then
0:55
motor one will be on. If switch two is
0:57
on and other two motor other two If
1:00
switch two is on and other two switches
1:02
are off then motor one will be on. If
1:05
switch three is on and other two motors
1:07
are off other two switches are off then
1:10
motor one will be on. And then if two
1:13
switches are on and the third one is off
1:16
then motor two will be on. And if all
1:18
the three switches are on then motor 3
1:20
will be on. So for this example we'll
1:23
use normally open contacts and normally
1:26
closed contacts. So let's move to
1:28
codices where we will draw a ladder
1:30
diagram. For this example
1:32
I will open codesses here.
1:46
Let's create a new project.
1:49
Let's select the template as standard
1:51
project and name as example
1:57
three. Okay.
2:02
After that we need to select latter
2:04
logic diagram and then click on okay.
2:10
Double click on PR PLCRG
2:14
and here we will draw the ladder
2:15
diagram. So firstly we will insert a
2:18
normally open contact here.
2:22
So this will be toggle switch one
2:26
to switch one.
2:29
So if switch one is on then
2:38
then here switch two and switch three
2:42
should be off. So we'll insert one more
2:45
normally closed contact here. So this
2:48
will be
2:50
switch
2:52
two
2:55
and then this will be switch three.
3:02
And then we'll insert a coil.
3:09
This will be motor
3:13
one.
3:16
So if switch one is on, switch two is
3:19
off, switch three is off, then the
3:21
signal will pass through this. As a
3:23
result, this motor one will be on.
3:28
Similarly,
3:31
when switch
3:34
two is on and switch one and switch
3:39
three should be off.
3:42
So use two more normally close contacts
3:44
here.
3:49
So this will be
3:54
switch one
3:57
and this will be
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this will be switch three.
4:07
So if switch two is on then switch one
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and switch three should be off then only
4:11
motor one will be on.
4:14
Then we need to connect here switch one,
4:17
switch two and switch three again here.
4:20
So for that I will show a trick here. So
4:22
we need to select all these switches
4:24
here. Switch one, switch two and switch
4:27
three and then insert a normally open
4:30
contact in paral.
4:33
So this will be switch three. So if
4:36
switch three is on then switch one and
4:40
switch two should be off. So we'll use
4:42
two normally close contacts here.
4:48
So this will be switch
4:51
one
4:53
and
5:01
this will be switch
5:04
two.
5:07
So for motor one to be on only one
5:10
switch should be on. Either switch one
5:13
or switch two or switch three should be
5:15
on and other two switches should be off.
5:18
If switch one is on, switch two and
5:20
switch three should be off. If switch
5:21
two is on, switch one and switch three
5:24
should be off. If switch three is on,
5:26
switch one and switch two should be off.
5:29
So when switch one is on the current the
5:32
uh the signal will pass through this and
5:34
then the signal will pass through this
5:37
only if when these two switches are in
5:39
false state because we have used two
5:41
normally closed contacts here to pass
5:44
the signal from here. These two normally
5:47
closed contact should be in false state.
5:49
Similarly when switch two is off the
5:52
signal should pass through this. So for
5:53
this switch one and switch three should
5:55
be off. Similarly when switch three is
5:57
on the signal should be passed from
5:59
here. So for that switch one and switch
6:02
two should be off.
6:04
After that we will insert a network
6:07
below. And here we'll insert a normally
6:11
open contact here
6:14
and this will be switch one.
6:21
And then we will so we need to turn on
6:25
motor two. So for for motor two to be on
6:28
two inputs should be on only two inputs
6:31
should be on. So we will insert one more
6:33
normally open contact here. So I will
6:37
click here
6:39
and then add a normally open contact. So
6:41
this will be switch two.
6:46
So if switch one and switch two and are
6:49
on then switch three should be off. So
6:51
we'll use normally close contact here
6:54
and this will be switch three. So switch
6:57
three should be on then the output will
7:00
be on. Then what will be on? Motor two
7:04
will be on. So this will be motor two.
7:07
Similarly here we have used two
7:10
switches. Switch one and switch two.
7:12
Similarly, switch two if switch two and
7:14
switch three are on and switch three is
7:16
uh switch uh switch one and switch three
7:19
are on and switch two is off then also
7:22
motor two will be on. So we will select
7:25
these two normally open contacts and
7:28
then insert
7:30
contact parallel.
7:32
So this will be switch
7:36
one.
7:38
If switch one and switch three are on,
7:42
so this will be switch
7:44
three are on and with that switch two
7:48
should be on. So we'll use normally
7:50
close contact here and this will be
7:53
switch
7:56
two. So switch two should be on. And
7:58
similarly we will select all these
8:01
contacts and insert
8:04
contact in parallel. Sorry,
8:07
we will
8:10
select all these and then insert a
8:12
normally open contact in part one. So
8:15
this will be
8:21
So this will be
8:24
switch
8:26
two
8:27
and then we will insert one more contact
8:34
and a normally closed contact. So this
8:37
will be switch three. So switch two and
8:41
switch three are on and switch one
8:44
should be off. Then only motor two will
8:48
be on
8:51
and then we will insert one more network
8:53
below here. So when all the three
8:56
switches are on then motor 3 will be on.
8:59
So in this case we will use three
9:01
contacts in series and a coil.
9:06
So for motor 3 the ladder diagram is
9:09
very simple. So this is switch one.
9:15
Then we have switch two.
9:20
Then we have switch three.
9:24
And then this is motor three.
9:35
So let's generate the code here.
9:40
Let's go online. After clicking on
9:43
simulation,
9:45
login.
9:47
Yes.
9:50
Start.
9:52
So as you can see here.
10:05
So all the three motors are off.
10:08
All the three motors are off. So to turn
10:12
on the motor one, we need to turn on
10:16
switch one.
10:19
We'll debug it and write values. You can
10:23
see motor one gets on. So we will turn
10:26
off switch one and turn on switch two.
10:29
Let's debug it. And you can see motor
10:32
one is also on. And then let's turn off
10:35
switch two and turn on switch three.
10:39
And you can see motor one is on. So when
10:43
we turn on only one switch, motor one
10:47
gets on. And if we turn on,
10:51
if we turn on switch one and switch two,
10:56
then the motor one gets off but two gets
10:59
on. So for motor one to be on only one
11:02
input should be on and other two inputs
11:04
should be off. But for motor two at
11:06
least two inputs should be on. Not at
11:08
least only two inputs should be on and
11:11
the third one should be off. Then motor
11:13
two will be on. So when we turn on motor
11:15
uh sorry switch one toggle switch one
11:17
and toggle switch two motor two gets on.
11:20
And if we turn on switch one and switch
11:23
three only
11:25
then also motor two gets on.
11:29
And then when we turn on switch two and
11:31
switch three and turn off switch one
11:33
then also motor two remains on. And when
11:38
you turn on switch one as well when we
11:41
turn on all the three switches then
11:43
motor two gets off but motor 3 gets on.
11:47
That was all about this example. Thank
11:49
you for watching.
11:52
[Music]