Ethernet cable

[jack0987]

An ethernet cable has 8 wires but only 2 seem to be used.
Would it be safe to use some of the other wires to communicate, for example using SPI, to a sensor?

 

[StudentSA]

As far as I know only four wires are used for communication on a typical cat5 Ethernet cable. That leaves 4 free; I think the blue and brown. There does not seem to be any reason why you could not use these for your own application?

Good point by the way however let someone more knowledgeable comment on this.

 

[Tipsy]

It depends on how the cable is implemented to how many wires are used. It is quite common to use one cable for ethernet and voice/telephony for instance. It should be fine to use it for other types of signal though. What's SPI?

 

[jack0987]

SPI - Serial Peripheral Interface
SPI Interface details

In this case I was thinking of a LAN - Local Area Network cable.

 

[arunb]

SPI is normally used for inter-connection between two devices on the same board, the cable lengths for an SPI communication should not be very long as it can pick up noise, also the signaling is normally at 5 V DC, so wires must not be long.

LAN is good when distances are large and when several devices have to be inter-connected.

Ideally the sensor must be connected to a control unit that receives the signals from the sensor and the control unit sends the received signals to a PC or another unit via Ethernet.

 

[jack0987]

I do not intend to use SPI for the reasons you mentioned.
RS232 may be a better choice.
The best choice may be to use the ethernet itself except for the added complexity and cost of the sensor hardware.
Not sure what to do at this point.

 

[Gary B]

The first pair (W/B) on pins 4&5 is normally telephone and is therefore available. The forth pair (W/Br) on pins 7&8 are defined as spare so are always available for your use. Ethernet uses the second and third pairs, or at least it has them reserved for GigaNet applications.

 

[jack0987]

Thanks Gary. That is very useful information.