use Ethernet to test circuit

Discussion in 'General Electronics Chat' started by abelcorver, Apr 30, 2010.

  1. abelcorver

    Thread Starter New Member

    Apr 10, 2010
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    Hey everyone,
    I'm very new to electronics, and one of my biggest issues is ensuring that part A of my circuit works, so that I can test part B without problems. Also, often I need to simulate some other part, because I´m not able to quickly build it (if at all).

    That's why I came up with the idea to use the 8 wires of the Ethernet cable to send signals to specific positions in my circuit, and test it this way. I've found some drivers that are hopefully going to allow me to send single bytes out...

    However, since there're only 8 wires, there doesn't seem to be a + and ground wire. So I was wondering, how can electricity possibly begin to flow from the "signal wires", since there's no ground...

    Does anyone know how this works?

    Regards,
    Abel.
     
  2. t06afre

    AAC Fanatic!

    May 11, 2009
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    I am not sure about what you are trying to do, it is often hard to describe electronics with words only. Could post some schematics, as it would help us to give you a proper answer.
     
  3. retched

    AAC Fanatic!

    Dec 5, 2009
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    http://en.wikipedia.org/wiki/Power_over_Ethernet

    POE or Power Over Ethernet may be what you are thinking of.

    What may be confusing you is, ethernet only uses 2 wires for communication. 1 for RECEIVE and 1 for TRANSMIT.

    You can use the a protocol like RS232 to transmit, by combining your raw binary data as packets. This may be easier (and inexpensive) to get you moving. Look up the MAX232 IC.
     
  4. rjenkins

    AAC Fanatic!

    Nov 6, 2005
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    10MBit or 100MBit Ethernet uses two Pairs of wires, one for transmit and one for receive. (Gigabit uses two pairs each way).

    The data pairs use differential drivers and receivers, and are transformer coupled at each end.

    The only thing an ethernet port can do is send bursts of data at 10MBit or higher, you cannot control individual signals.

    You could use a parallel printer port if your machine has one. Even if there is not one externally, many desktop motherboards include it but the machine builders don't bother adding the cable & backplate, which is a standard part.
    (Or you can buy parallel port add-on PCI cards).

    The parallel printer port uses simple TTL logic levels and has a number of inputs and outputs, so is easy to use with DIY projects.

    Just be very careful you do not ever feed voltage in to the port while the PC is off, as that can wreck the port or the whole motherboard. Only use open-collector signals and pullup resistors.
     
  5. abelcorver

    Thread Starter New Member

    Apr 10, 2010
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    Hey, thanks you all for your replies!
    I don't ahve any schematics. My question boils down to: How can I use the ~3-5V voltages on my ethernet cable as input to my circuits.

    Thank you for your suggestions. However, for some reason, my cable really does have 8 wires. I did some research and I think I have a Category 5 cable. So wouldn't that be Ethernet?

    Yeah, I suspected I wouldn't be able to write at lower speeds, but what I meant with control over my "signals" is that I could write like 10MB of data with the 6th bit turned on, and the others off, so that I'd practically send a ~1 sec signal over my 6th wires (assuming each wire carries one signal).

    Thanks in advance!

    Cheers,
    Abel.
     
  6. rjenkins

    AAC Fanatic!

    Nov 6, 2005
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    Ethernet is a complex protocol, you cannot send arbitary data to the port.

    The PC communicates with an interface IC, dedicated to the ethernet system.
    That chip is designed to send ethernet 'frames' which include a data run-in, framing codes, addresses etc as well as the actual data to be sent.

    Also, Ethernet data is sent using Manchester coding. This means there are continuous transitions, both for clock recovery and to allow it to be coupled via the isolating transformers.

    There are other complications like the 'presence pulse' and speed negotiation signals before any true data can be sent.

    The only thing you can usefully connect an Ethernet port to is another Ethernet port.
    You are not the first person to think of this and I very much doubt you will be the last.

    (For info, the original twisted-pair ethernet spec only used two of the four pairs. The middle pair was left vacant so the sockets & cabling could also be used for phone wiring - if an RJ11 phone plug is put in an RJ45 ethernet socket, it connects to the middle pair. All normal Ethernet cabling is four pair anyway.)
     
  7. abelcorver

    Thread Starter New Member

    Apr 10, 2010
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    Ok, well, too bad I guess :p

    Does anyone have any ideas about how to test parts of my circuit.
    Moreover, I have an EEPROM IC with 8 pins, and I want to connect it to some microprocessor, however, how can I possibly test if everything works fine?

    Does anyone have any experience with this ?
    If you ever programmed EEPROM, or used a microprocessor in your circuit, how did you start out?

    Thanks in advance!

    Cheers!
    Abel.
     
  8. kingdano

    Member

    Apr 14, 2010
    377
    19
    i started with a basic stamp kit from parallax - they have great step by step learning books that they sell as education kits - they do use an I2C (pronounced eye-squared-see) EEPROM in their books at times - this may not be an exact match - but the basic ideas are likely similar.

    http://www.parallax.com/tabid/182/List/0/CategoryID/67/Level/a/SortField/0/Default.aspx


    also, depending on the interface of the eeprom chip - youc an potentially use an item from total phase which allows you to (through a PC) act as a host OR slave device for quite a few common EEPROM devices - check them out.

    (link OK mods? i dont work there! they just make great stuff for development - we use them at work in our manufacturing process now - my suggestion of course ;))

    http://www.totalphase.com/

    can you tell us what device you are using?
     
  9. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
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    The CAT5 ethernet cable DOES have 8 wires in it. But the ethernet PROTOCOL talks over twisted pair. 2 sends and 2 recieves. That leaves 4 extra wires in the CAT5 cable to be used for other things.

    Did you check the link I posted to POE? It shows the 8 wires and what they do.

    http://en.wikipedia.org/wiki/Power_over_Ethernet#Notes

    this is the list of the 8 pins or "wires" on your cable and what the ETHERNET protocol uses them for.

    You can use them for whatever youd like.

    As for the EEPROM IC you are planning on using, The datasheet should have the protocols and pins that are required to tie the IC to a microController.
     
  10. abelcorver

    Thread Starter New Member

    Apr 10, 2010
    14
    0
    Yeah, I also thought about buying one of these sets.
    Also, the EEPROM programming kit looks very nice, but
    unfortunately it's also way too expensive :( :p

    Yeah, I saw the table explaining the 8 wires regarding Power over Ethernet, however I didn't know if they were applicable to my wire, and the 'common' ethernet protocol my computer uses for that matter...

    I'm still a student, and I'm very low on cash right now ... (as you can probably imagine) ;)

    Do you know any basic / improvised methods to get started with this?

    Regards,
    Abel.
     
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