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RS232 vs IC2 signal distance — Parallax Forums

RS232 vs IC2 signal distance

eagletalontimeagletalontim Posts: 1,399
edited 2012-01-29 05:04 in Propeller 1
Quick question....Does anyone know the max distance for both of these? I am wanting to run my display up to 4 feet away from the main circuit and was wondering if either of those 2 setups could handle that distance. I am thinking RS232 is more reliable, but I would prefer to have some feedback on that before I begin my circuit design.

Comments

  • RaymanRayman Posts: 14,848
    edited 2012-01-28 18:27
    4 feet is probably pushing it for regular I2C at high speeds. It would probably work fine at low speeds though.

    RS232 was meant for long runs, especially the +/- ~10 volt version. The TTL version of RS232 would be good for several feet too.

    I2C is really meant for close range comms, so at 4 feet I think I'd recommend RS232. But, I think either would work.
  • eagletalontimeagletalontim Posts: 1,399
    edited 2012-01-28 18:36
    That is what I had figured, but I was not 100% on the distance of the RS232. The RS232 is for a display that can run from either 5v or 3.3v. I will probably be running it from it's own 5v source due to the current draw I am already at with my current design.
  • T ChapT Chap Posts: 4,223
    edited 2012-01-28 18:45
    Using lower speed i2c drivers (see the minimal i2c), I have used i2c on unshielded cables for runs between 25' and 35' on many residential projects with no failures after years of use. I did ultimately add an i2c buffer that is designed to be more reliable for longer i2c runs. I forget the part number but you can google 'i2c extender' and look at some of the NXP P82Bxxx devices that are easy to add to a design. They do suggest a twisted pair, a CAT5 cable contains 4 sets of twisted pairs. Depending on how noisy your environment is for the project, you may get away with just running the i2c over the distance without a buffer. At low speeds with the minimal driver in an environment that does not have a lot of noise, you will probably be fine.
  • Peter JakackiPeter Jakacki Posts: 10,193
    edited 2012-01-28 19:15
    RS232 is fine for 100's of feet and unless you were running past variable frequency drive I would doubt that at the speeds you would be using that there would be any problems running 4'.

    Like others I have run I2C for much greater distance than they were originally designed for (internal to a TV chassis). If running I2C means you can avoid implementing RS232 then by all means use I2C. However I would use a separate I2C bus from your onboard I2C which may only just be the EEPROM. Also I would use lower values of resistors on the bus, nominally 2.2K for instance. There is no need for special cable of buffers over what is essentially an arm's length. Keep it simple.
  • eagletalontimeagletalontim Posts: 1,399
    edited 2012-01-28 20:21
    Ok, I will try the I2C since I will not have to implement RS232. If it does not work for my application, I will have to convert to RS232.
  • Duane C. JohnsonDuane C. Johnson Posts: 955
    edited 2012-01-29 05:04
    Be a bit careful.

    Basically RS-232 uses direct one way drivers.

    I2C uses open drain drivers with pull up resisters, is bidirectional, and can be connected to multiple devices.
    If you use I2C use separate pins from any other deices and minimum acceptable pull up resisters values.

    Duane.
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