Specification of I/O

We start with analysing the task to decide what hardware to use.

Digital Outputs

We have four traffic lights, but the traffic lights in the same street can be connected in
parallel, which means that we can treat them as two lights.

Three outputs per light: 2 * 3 = 6
Indication: Operating mode 1
Indication: Control 1
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Total number of digital outputs: 8

Digital Inputs

The only digital input needed is for the maintenance technician's switch. The operator controls
the process from the computer display, and this requires no physical signals.

Switch: Operating mode 1
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Total number of digital inputs: 1

Analog I/O

No analog in- or outputs are needed for this task.

Specification of the Process Station

When we have decided upon the I/O needed, we can choose the hardware. We choose:

1 Linux PC with rack
1 card with 16 digital inputs
1 card with 16 digital outputs

Specification of the Operator Station

1 Linux PC

Specification of Plant Graphics

We need a display from which the operator can control and survey the traffic lights.