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page 132

9. MECHATRONICS CIRCUITS

• These circuits have been selected to be useful for interfacing controls or electronics to physical devices.

9.1 POWER SWITCHING

9.2 USER INPUT/OUTPUT

9.2.1 Multiplexing

Large numbers of inputs and outputs tend to use PLCs inefficiently.

Consider the example of 16 buttons in a keypad. If we connect each button to an input, 16 inputs will be required. But, it is also possible to connect the buttons to 4 outputs and 4 inputs.

OUTPUTS

push-button switches

 

connect output lines

 

to input lines

 

INPUTS

• A similar multiplexing technique can be used for output, as is commonly done for LED digit displays. (Most red LED displays look constant, but they actually flicker at more than 30Hz).

page 133

 

BCD to

PLC outputs

7 segment

 

display

 

driver

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