Shop OBEX P1 Docs P2 Docs Learn Events
TTL voltage- max cable length run — Parallax Forums

TTL voltage- max cable length run

rob jacksonrob jackson Posts: 23
edited 2007-10-13 20:25 in BASIC Stamp
Sorry to be a pain guys.

I've done some quick searches with no luck.

I'm wondering how long of a cable I can run the·outputs of the·BS2 without amping them.· I'm sure it comes down to wire guage etc...

But for the sake of arguement lets try and use a standard IEEE cable.

Can I run 15-20 feet?

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Thank You,


Rob Jackson
oleancomputers.com

Comments

  • PJAllenPJAllen Banned Posts: 5,065
    edited 2007-10-13 14:44
    Why not just try something?
  • stamptrolstamptrol Posts: 1,731
    edited 2007-10-13 14:45
    Rob,

    As long as you're not trying to draw large currents, TTL signals can be reliably used for the distance you mentioned. Keep cables separate from cables carrying motor currents.

    Don't forget, the Stamp pins can only deliver about 20 mA by themselves. Ordinary CAT5 cable will work fine, or use #22 stranded if much flexing is expected.

    Cheers,

    Tom Sisk

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Tom Sisk

    http://www.siskconsult.com
    ·
  • rob jacksonrob jackson Posts: 23
    edited 2007-10-13 14:55
    Thanks Tom. Was hoping so.

    PJ- I'd rather hear an answer from experience.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Thank You,


    Rob Jackson
    oleancomputers.com
  • Steve JoblinSteve Joblin Posts: 784
    edited 2007-10-13 15:21
    I'm not an expert, but I THINK I remember reading that 25' was the stated "max" length... I'm sure you can get even greater distances reliably, but I believe that there are no issues "guaranteed" up to 25 feet.
  • Mike GreenMike Green Posts: 23,101
    edited 2007-10-13 15:32
    The "reliable" distance is inversely related to the signalling rate. If your signalling rate is low (several KHz) , the distance can be longer, expecially if you use twisted pair or shielded cables. If you're trying to get MHz rate data over 15-20 feet, you have to be careful about noise pickup, matched impedances, etc. It helps to use a higher voltage level at that distance ... up to several hundred feet. That's why people switch to RS232 or RS485 much beyond 20-50 feet.
  • Steve JoblinSteve Joblin Posts: 784
    edited 2007-10-13 15:59
    Thanks Mike for setting me straight! I learned my new lesson for the day!
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2007-10-13 18:19
    It is often helpful to load the receiving end with a resistor or resistive divider. The value(s) used will depend on the logic family used there and the resistance of the cable. The extra load forces the cable to carry more current, which makes it less susceptible to noise pickup.

    -Phil
  • rob jacksonrob jackson Posts: 23
    edited 2007-10-13 18:56
    Great information guys. This is for remote panel controls to get a safe distance from a high reving engine.

    -Will be trying to run a RC servo - throttle control.
    -Pickup a tach signal. still working out the how yet. 0-1800rpms
    -And just general solidstate relays.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Thank You,


    Rob Jackson
    oleancomputers.com
  • pwillardpwillard Posts: 321
    edited 2007-10-13 20:25
    If you are sending serial data using SEROUT/SERIN or SHIFTOUT/SHIFTIN or even PWM type commands you can easily have noise issues.

    Signal to noise ratio is what will get you in the end. At the extreme end of the cable the RECEIVER is most sensitive to the strong signal of the local TRANSMITTER in two way communications. I didn't see anything about this yet so I figured I'd chime in. Good grounding can keep this under control.

    You will have the best luck if using CAT-5 style cable to ground 1 member of a twisted pair and send a signal in the other member of the pair. This will help keep random noise from being introduced or from output signal cross-over from jumping into your input end.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔

    There's nothing like a new idea and a warm soldering iron.
Sign In or Register to comment.