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Hall sensor A1122LUA-T resistance

Discussion in 'Sensors and Actuators' started by Jeroen Humasol, Nov 28, 2015.

  1. Jeroen Humasol

    Jeroen Humasol

    68
    4
    Nov 8, 2015
    Hello everybody,

    I bought a Hall sensor to measure the rotation speed of a shaft.

    I was trying to install the hall sensor on my bradboard when is stumbled upon a problem. I just couldn't figure out how big the resistance between VCC and Vout should be. At page 12 of the datasheet there's a small sketch of the circuit where the resistance is called R_L. (datasheet: http://www.farnell.com/datasheets/1804644.pdf)

    How can I get the needed resistance out of the information on the datasheet?

    Thanks!
     
  2. Minder

    Minder

    2,836
    586
    Apr 24, 2015
    You need to size the resistor based on the voltage you are using on the output.
    The output consists of a open drain mosfet with a max drain current of 25ma.
    So calculate the minimum resistor value based on the voltage used, also allow for any resistance in the load itself, i.e. sourcing resistor etc.
    M.
     
    Jeroen Humasol likes this.
  3. eetech00

    eetech00

    95
    8
    Nov 17, 2014
    Hi

    Quote from datasheet.
    " After turn-on, the output voltage is VOUT(SAT) . The output transistor is capable of sinking current up to the short circuit current limit, IOM, which is a minimum of 30 mA".

    That basically means 30ma load is a short circuit.
    What is the Vout pin going to connect to?.
     
  4. Minder

    Minder

    2,836
    586
    Apr 24, 2015
    The vout pin connects to whatever device is sensing the output, it is a little low to drive any device direct, it is common to input into a high impedance device such as a TTL or microP.
    If you use a opto isolator for example the series resistor of the opto has to be taken into account.
    What do you intend mating the sensor with?
    What voltage.
    M.
     
  5. eetech00

    eetech00

    95
    8
    Nov 17, 2014
    If VCC is 5v, and interfacing to 5v TTL device input, just connect a pull up resistor (2.2k - 4.7k) from VCC to Vout, then connect Vout to device.
     
  6. Minder

    Minder

    2,836
    586
    Apr 24, 2015
    I think that is basically what I said, the OP would need to show what he intends driving and what Vs supply.
    M.
     
  7. Jeroen Humasol

    Jeroen Humasol

    68
    4
    Nov 8, 2015
    Hey guys,

    Once again thanks for the quick responses!

    I'm going to supply the circuit with 5V coming from my arduino. The measured voltage will also be sent to an analog input pin of the arduino.
    Is it then like this: Max current=25mA like indicated here as Iout upload_2015-11-29_15-31-28.png
    So according to ohms law, the resistance should minimum be:R=U/I=5V/0.025A= 200Ohm. Since this is used as a pull up resistance, is there no maximum/ideal value for this resistance? All i'm wondering is: with what value of resistor will my sensor last the longest?
     
  8. Minder

    Minder

    2,836
    586
    Apr 24, 2015
    A 330-470 ohm resistor minimum will work, I have used a 1k in similar applications.
    M.
     
    Jeroen Humasol likes this.
  9. Jeroen Humasol

    Jeroen Humasol

    68
    4
    Nov 8, 2015
    Thanks for the help!
     
  10. Bluejets

    Bluejets

    3,453
    698
    Oct 5, 2014
    For 5v arduino boards, 3v is considered a high signal.
    For 3.3v arduino boards, 2v is considered a high signal.
     
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