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Power, Clock and Data on 6 Wires? — Parallax Forums

Power, Clock and Data on 6 Wires?

Duane DegnDuane Degn Posts: 10,588
edited 2013-05-16 15:42 in General Discussion
I'm about to deliver this project to my niece in the hospital. I thought it would be a good idea if there were a bit more room between the controller box and the start of the LED strip so I'm about to make an extension cord for it.

My plan is to use 6-wire Cat 3 cable. It has three twisted pairs. I've read several places that a data line twisted with a ground or power line will have less noise issues than the wire alone. I believe it would be a bad idea to have both the data and clock lines on a single pair.

So what's the best way of doing this? Data and ground, clock and 5V, with the last pair unused? Can I use the extra pair for 5V and ground (each would use two wires) to reduce the resistance?

I'm planning on making the extension somewhere around three to five feet. These LEDs can draw up to 2.5A.

Do any of you see a problem with my extension wire plan?

A quick answer would be appreciated. I would like to start soldering the connections in about ten minutes.

BTW, I also have Cat 5 wire I could use. Any advantages to using the Cat 5 over the Cat 3?

Thanks,

Comments

  • Tracy AllenTracy Allen Posts: 6,658
    edited 2013-05-16 14:34
    10 minutes -- well, I happened to check in here only a minute to spare! My immediate reaction for the 3 pairs is, data+ground, clock+ground, Vdd+ground. The twisting in pairs is the thing to help avoid crosstalk. I think your scheme with data+ground and clock+power would work fine too. It it is i2c, lower value pullup resistors can help.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2013-05-16 14:41
    Tracy Allen wrote: »
    10 minutes -- well, I happened to check in here only a minute to spare! My immediate reaction for the 3 pairs is, data+ground, clock+ground, Vdd+ground. The twisting in pairs is the thing to help avoid crosstalk. I think your scheme with data+ground and clock+power would work fine too. It it is i2c, lower value pullup resistors can help.

    Thank you very much Tracy!

    Good to know about the pull-up resistors. I don't think I'll try it this time (the board is all sealed up in the enclosure). I don't think the extension wire will be critical, but the LEDs may look better it they start a few feet away (hopefully on the wall).

    Thank you again.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2013-05-16 14:45
    I think I'll use the Cat 5 cable. Data/ground, clock/ground and a pair each for 5V and ground.

    Besides, I have lots of Cat 5 cable.
  • tonyp12tonyp12 Posts: 1,950
    edited 2013-05-16 14:45
    A signal is only as good as its return (ground), so with my new SSR project I dedicated ground for each signal.
    As I don't want for example 3 high signals to fight for one ground return, and on long cable runs it matters.

    Follow the RJ12/25 standard where the inner pins make up a pair (a twisted pair for less crosstalk)
    and could also be a good idea to stick to same + - that cat3 uses.
    http://en.wikipedia.org/wiki/Registered_jack#Pinouts
  • WBA ConsultingWBA Consulting Posts: 2,933
    edited 2013-05-16 14:46
    Ditto for Tracy's response or here is another method that I used on 208 feet of Cat 5 for a Sensirion SHT11 sensor with no issues:

    Blue
    Vdd
    Blue/Wht----Clock
    Green
    Gnd
    Green/Wht----Data
  • Duane DegnDuane Degn Posts: 10,588
    edited 2013-05-16 14:53
    tonyp12 wrote: »
    A signal is only as good as its return (ground), so with my new SSR project I dedicated ground for each signal.
    As I don't want for example 3 high signals to fight for one ground return, and on long cable runs it matters.

    Follow the RJ12/25 standard where the inner pins make up a pair (a twisted pair for less crosstalk)
    and could also be a good idea to stick to same + - that cat3 uses.
    http://en.wikipedia.org/wiki/Registered_jack#Pinouts

    Thanks Tony,

    I'm not going to be using a RJ type jack. I have an extra set of connectors the used by the LED strip.

    11272-03a_medium.jpg

    (The top two.)

    I'm make sure and take your advice about using the standard polarity if I make some sort of adaptor. I considered making an adaptor with RF connections to make using Cat 5 or Cat 3 wire with these LEDs easier in the future. I may still make an adaptor when I get my LEDs back (probably in about three weeks).
  • xanaduxanadu Posts: 3,347
    edited 2013-05-16 14:59
    I think that twisted pair works best with a circuit using differential signaling. http://en.wikipedia.org/wiki/Differential_signaling

    Otherwise twisting the wires just ensures they're both subjected to the same amount of EMI. The circuit connected is usually what "reduces" the noise on the line though.
  • xanaduxanadu Posts: 3,347
    edited 2013-05-16 15:11
    Duane the idea of cheerful mood lighting in a hospital is Brilliant. Well done.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2013-05-16 15:42
    After seeing Andrew's success, I decided to try a 9' extension. So far so good. It appears to be working.

    Thanks everyone.

    @xanadu, Thanks for the comments. Apparently twisting a data and clock line together can cause problems. I read an appnote suggesting data and clock line be separated with either ground or power lines (I think this was on a ribbon cable). I was pretty sure I didn't want the data and clock to share a pair of wires.
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