Hall switch

Discussion in 'Digital Circuit Design' started by ghebaur, Sep 7, 2016.

  1. ghebaur

    Thread Starter Member

    Jun 17, 2014
    30
    1
    Hello,

    I am trying to find the right hall effect sensor to use it as a SWITCH with an MPC23017 I/O expander for a matrix "keypad". For multiple-key press i will use diodes like in the scheme below.
    http://www.musicfromouterspace.com/...ES/CONTROLLERS/images4/reeds_and_diodes_2.gif

    The hall switchs will replace the mechanical switchs and it will have to act as a normally open switch when there is no magnetic field present and it will need to close the circuit when a magnetic field is present.

    My question is. What kind o hall switch i need to use so i won't need to add other external components? What too look for in a datasheet to know that i got the right hall sensor?
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,553
    2,375
    There is the miniature Honeywell SS400 series, you will need a tiny button magnet etc to complement it.
    Max.
     
  3. ghebaur

    Thread Starter Member

    Jun 17, 2014
    30
    1
    That's the type of hall switch i'm looking for but you have not understood my question. I need to identify the characteristics that allow me choose the sensor that fits my application.

    I saw in a lot of circuits that they use a 'pull-up' resistor and the switch acts as a normally closed switch. I need it to do the exact opposite thing and without the resistor (other additional components).
     
    Last edited: Sep 12, 2016
  4. shteii01

    AAC Fanatic!

    Feb 19, 2010
    3,394
    497
    I install Hall Effect switches in industrial applications. We get the sealed unit with a four pin connector on the end. No other components. Just hook it up to 24 volts. Of course the output of such unit (designed to work with 24 volt Allen-Bradley PLC or similar PLC) is also about 24 volts. If you feed it directly to the 5 volt uC, you will fry it. Perhaps a voltage divider on the uC end.
     
  5. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,801
    1,105
    :confused: Seems you want it both ways? If you want it the first way then a Hall switch of the 'open collector' type should do. The MPC23017 has 100k internal pull-up resistors which can be selectively enabled using the GPPU register.
     
    Last edited: Sep 11, 2016
  6. ghebaur

    Thread Starter Member

    Jun 17, 2014
    30
    1
    Sorry, in the second quotation you made i meant 'normally closed'. I will try your suggestion and i'll come back with the results, some 3144 hall sensor, cheapest on aliexpress :D. Thanks.

    @shteii01 24V is too much for my application which will be at most 5V. And the sensors should be as small as possible.
     
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