Results 1 to 9 of 9

Thread: I2C host controller

  1. #1

    I2C host controller

    Hi all,

    I am looking at some I2C stuff. The Devantech usb-12C host controller can be used with the I2C expension board, right? How many I2C device can I hook up to that host controller?

    any suggestions to use something else?

    thanks,

    Ron


  2. #2
    Join Date
    May 2008
    Posts
    2,228
    Images
    155
    Rep Power
    125

    Re: I2C host controller

    Quote Originally Posted by csdude View Post
    Hi all,

    I am looking at some I2C stuff. The Devantech usb-12C host controller can be used with the I2C expension board, right? How many I2C device can I hook up to that host controller?

    any suggestions to use something else?

    thanks,

    Ron
    Most of the Devantech devices (and really, most low-cost hobby I2C stuff) use 7-bit address, so 128 devices is the max on the bus (there is a 10-bit address mode, but it's far less commonly supported). Your actual usage may be less depending on the devices themselves. For instance, the SRF-08/02 sonars have 16 possible addresses, so you can't attach more than 16 of either device.

    One issue with I2C to be careful with is bus capacitance. I2C was really intended for multiple devices on a single PCB, not for stringing together all sorts of components inside a robot. You'll want to keep the wire runs as short as possible in most cases. Thus, again, you may not actually be able to toss 128 devices on there before you have too much bus capacitance...

    -Fergs

  3. #3

    Re: I2C host controller

    Quote Originally Posted by lnxfergy View Post
    Most of the Devantech devices (and really, most low-cost hobby I2C stuff) use 7-bit address, so 128 devices is the max on the bus (there is a 10-bit address mode, but it's far less commonly supported). Your actual usage may be less depending on the devices themselves. For instance, the SRF-08/02 sonars have 16 possible addresses, so you can't attach more than 16 of either device.

    One issue with I2C to be careful with is bus capacitance. I2C was really intended for multiple devices on a single PCB, not for stringing together all sorts of components inside a robot. You'll want to keep the wire runs as short as possible in most cases. Thus, again, you may not actually be able to toss 128 devices on there before you have too much bus capacitance...

    -Fergs
    Ah, ok, cool. Thing is .. there are a lot of interesting sensors out there, but a lot of them have an I2C interface. would be cool if you could string a bunch of them together instead of using a host controller for each and every device.

  4. #4
    Join Date
    May 2008
    Posts
    2,228
    Images
    155
    Rep Power
    125

    Re: I2C host controller

    Quote Originally Posted by csdude View Post
    Ah, ok, cool. Thing is .. there are a lot of interesting sensors out there, but a lot of them have an I2C interface. would be cool if you could string a bunch of them together instead of using a host controller for each and every device.
    Yeah, I2C works pretty well, as long as you look out for bus capacitance.

    -Mike

  5. #5

    Re: I2C host controller

    Quote Originally Posted by lnxfergy View Post
    Yeah, I2C works pretty well, as long as you look out for bus capacitance.

    -Mike
    Ok, I am kinda a rookie with that, how do I avoid that best?

  6. #6
    Join Date
    May 2008
    Location
    TN
    Posts
    853
    Images
    99
    Rep Power
    71

    Re: I2C host controller

    Short wires, and if they must be long then be careful with the routing.

    Edit: A note about capacitance in regards to wiring. Whenever you place something on a wire to complete a circuit it adds a certain amount of capacitance, resistance, and inductance. The capacitance is parallel to the circuit and the inductance is serial as is the resistance. As those attributes increase, it will affect the circuit to a greater degree. The capacitance and resistance will form and RC time circuit that will affect the slew rate of any data. That may not be a big deal at low frequencies but as the speed increases then it becomes more of a bad thing. The best way to avoid it is to try not to use long wire runs.
    Last edited by jes1510; 01-15-2010 at 10:55 AM.
    "If A is a success in life, then A equals x plus y plus z. Work is x; y is play; and z is keeping your mouth shut."
    -
    Einstein

    Don't be a HelpVampire

  7. #7

    Re: I2C host controller

    Quote Originally Posted by jes1510 View Post
    Short wires, and if they must be long then be careful with the routing.
    ok, shielded wire would help?

  8. #8
    Join Date
    Apr 2008
    Location
    Sacramento, CA, USA Area
    Posts
    5,341
    Rep Power
    174

    Re: I2C host controller

    Shielded could help with inductance. Heavier gauge will help with resistance. But then your capacitance goes up.

    Extremely short, shielded, heavy gauge. That should address everything.
    I Void Warranties´┐Ż

  9. #9

    Re: I2C host controller

    Quote Originally Posted by Adrenalynn View Post
    Shielded could help with inductance. Heavier gauge will help with resistance. But then your capacitance goes up.

    Extremely short, shielded, heavy gauge. That should address everything.
    Hmmm, I can probably come up with something there....

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Problems connecting PS2 controller to Axon
    By JadeKnight in forum Arbotix, Microcontrollers, Arduino
    Replies: 11
    Last Post: 09-26-2009, 07:21 PM
  2. RC & Serial Servo Controller Kit
    By Al1970 in forum Garage Sale
    Replies: 0
    Last Post: 01-10-2009, 12:39 AM
  3. Question(s) Motor controller ?'s
    By sthmck in forum Arbotix, Microcontrollers, Arduino
    Replies: 4
    Last Post: 11-06-2008, 03:29 PM
  4. Controlling Servos with a servo controller
    By bodhibuilder in forum Arbotix, Microcontrollers, Arduino
    Replies: 25
    Last Post: 09-29-2008, 11:07 AM
  5. Contest Entry Digital Slot Car Controller
    By wrighthobbies in forum Project Showcase
    Replies: 1
    Last Post: 09-21-2007, 01:05 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •