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Signal integrity and Cables... — Parallax Forums

Signal integrity and Cables...

rwgast_logicdesignrwgast_logicdesign Posts: 1,464
edited 2012-11-14 19:48 in General Discussion
Ok so I dont have a scope and im not real sure what the best practice in this situation is...

I have two motors each have a piece of flat ide like 6 conductor cable with a female header on the end, the length of these wires is 6cm. The 6 conductors are +18v, Motor Ground, +5v, Logic Gorund, Hall based Encoder A, Hall based encoder B. My issue is I need to extend these cable we will say a MAXIMUM of 6 inches probably more like three or 4 though. If I just use some cheap cat5 (have spools of it so its easily available and pleantiful) to extend the 6 wires will I have any issues getting a clean signal off my encoders? What if I just used 6 wires heat shrinked maybe wrapped in foil? In this instance would a 74xx244 or 74xx425 maybe help boot the signal, I know it will help clean them via its schmitt triggers, but there waves already look good no need to clean the signal if exxtending the wire lenghts is gonna be ok.

I plan to have all kinds of sensors that will probably need 6 inch extensions on them in this project, I know twisting the cables helps but is there anything i need to take in to special consideration?

Comments

  • kwinnkwinn Posts: 8,697
    edited 2012-11-14 11:38
    Make sure you put the +18V and Motor Ground on one pair of wires and you should be OK. To be absolutely sure put the +5 and Logic Ground on another pair.
  • Mark_TMark_T Posts: 1,981
    edited 2012-11-14 16:20
    I think each encoder signal needs to be paired with logic ground - first priority - then the noisy supply (18V motor, presume PWM'd) should have its own pair with its motor ground. 5V logic supply won't matter really, its already decoupled at both ends I suspect, but hey there's a spare pair of wires...

    To be more paranoid take the motor supply and ground along a separate twisted pair away from logic level signals - should further precaution be needed.

    [ for 6 inches this is overkill of course! ]
  • NWCCTVNWCCTV Posts: 3,629
    edited 2012-11-14 19:48
    Not that it matters as far as this issue goes, but is the CAT 5 cable twisted or solid? If it is solid just be careful with it as I have seen many instances of it breaking after using a few times.
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