Introduction to Industrial Automation

10.8   An Automated Billiard Table Controlled by a PLC

This application is outside the industrial world, but includes operations very common in industrial 

processes, such as multi-input counting, signaling, and multiple phases of operation and detec-

tion. Figure 10.8 shows an automated billiard table controlled by a small PLC. The specifications 

of operation are the following:

  1. During the game, balls fall from the four corners of the table and are detected by four photo 

switches F

1

, F

2

, F

3

, and F

4

, while all are gravity-driven to the ball box. Of course, how many 

balls are going to fall at each corner is a quite random event.  

  2.  The table operates with a coin slot machine. In order for a coin to be accepted by the coin box, 

it is necessary for button b to be pressed, and all nine balls to be present in the ball box. Also, 

the solenoid SL must be energized in order for the coin to be driven to the coin box. If for 

any reason the SL is not energized, the coin comes out in the coin return slot.

  3. Just after the detection of a coin by the photo switch F

5

, the SL must be deactivated because 

during the game, the slot machine does not accept other coins but returns them to the 

player.

Feeder

M

A

B

C

+24 V DC

+24 V DC

0 V

0 V

F

1

F

1

PN

1

PN

2

F

2

F

3

F

2

F

3

PN

1

PN

2

On

M

FD

Off

PLC

I0.1

Q2.2

Q2.4

Q3.0

Q3.2

I0.2

I0.3

I0.4

I0.5

Inputs

Outputs