How does the ethernet cable communicate between the computer and router?

[sadpony]

I read about the ethernet over twisted pair pin outs, there were some Tx+, Tx-, Rx+, Rx- pins. I didn't understand what are the different voltage levels on those pins. I actually want to turn ON and OFF a light source on the basis of 1s and 0s sent on those pins. Can anyone tell me what modulation technique is used and how can I separate individual pins and convert the data into series of 1s and 0s.

I want to connect light source to the router and photodiode to the computer.

Please do reply.
Thanking in advance.

 

[throwaway18]

The details of communication over ethernet are fairly complex.
The usual choice for a hobby project is an arduino with an ethernet shield, that makes it fairly easy.

The data encoding is different at 10/100/1000Mbps speeds, there is usually an isolation transformer in each ethernet port, the data has to be formatted into ethernet frames and it is normal to use another protocol such as tcp/ip inside the ethernet frames. For tcp/ip you usually also need to implement DHCP and ARP.

To learn some details of the hardware interface you can start with this wikipedia article.
https://en.wikipedia.org/wiki/Ethernet_over_twisted_pair