Understanding datasheet sensor

Discussion in 'Embedded Systems and Microcontrollers' started by enjoytech, Oct 10, 2014.

  1. enjoytech

    Thread Starter New Member

    Oct 10, 2014
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    Hi,
    I need yours help for reading correctly datasheet of my sht11 sensor.
    I should synchronize the comunication with it and I don't understanding the meaning of empty entries of this table.
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    The empty entries are explained in the notes below the table. In order to help you you should give us a link to the entire datasheet.
     
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    The device is using something called "I2C" for Inter-Integrated Circuit communication.

    Google I2C along with the mystery processor you use and you will see how to drive this.
     
  4. enjoytech

    Thread Starter New Member

    Oct 10, 2014
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    I can't use I2c but I should send bit once to once.
     
  5. Papabravo

    Expert

    Feb 24, 2006
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    That doesn't make much sense. What are you trying to say?
     
  6. enjoytech

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    Oct 10, 2014
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  7. enjoytech

    Thread Starter New Member

    Oct 10, 2014
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    I read page 5 of datasheet where it says: "The serial interface of the SHT1x is optimized for sensor readout and effective power consumption. The sensor cannot be addressed by I2C protocol; however, the sensor can be connected to an I2C bus without interference with other devices connected to the bus. The controller must switch between the protocols. "
    I think that for serial interface I have to send bit for comand once at once
     
  8. Papabravo

    Expert

    Feb 24, 2006
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    So I think I understand what is going on. Instead of making their device compatible with all the other I2C devices in the world they are insisting that the microcontroller abandon the perfectly good I2C hardware machine inside the microcontroller and go back to bit banging a variation on I2C just for their part. If that's what they want, then that is what you have to do. Do you understand their variant of the protocol well enough to write a bit banging driver?

    I might be willing to do it for you for the right price and the cost of the tools.
     
  9. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Damn, they messed this chip up, huh? Only thing to do is sit down with Figure 17 and bit bang in and out all the clocks and data items.
     
  10. enjoytech

    Thread Starter New Member

    Oct 10, 2014
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    thank you for your reply but I want only to know the value of Tsckh/ Tsckl in typ and max column. I don't understand if it is 100 ns or not?
     
  11. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    They say that minimum is 100 ns. So if you make it less then 100 ns, it will not work.
     
  12. ErnieM

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    Apr 24, 2011
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    Tsckh + Tschl = 100 + 100 = 200nS. Invert that and you get 5MHz, the max speed of the device (Fsck).

    Note the minimum is zero, meaning there is no lower speed limit.
     
  13. Papabravo

    Expert

    Feb 24, 2006
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    There are not many processors you can bit bang at that rate so who cares what the maximum rate is. Like air travel -- you can't get there from here.

    Ahhh.....cha-cha=cha
     
  14. MrChips

    Moderator

    Oct 2, 2009
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    You need to pay attention to the cable length, capacitance and pull-up resistor on the DATA pin.

    The DATA pin is tri-state bidirectional and requires a pull-up resistor (e.g. 10k-ohm).

    You need proper DATA setup and hold times. For best reliability, I would choose much longer times, e.g. 1-10us.

    I use 20us CLK with a 20cm cable.
     
  15. enjoytech

    Thread Starter New Member

    Oct 10, 2014
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    thank you very much, I'll follow your advices
     
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