Hall switch

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

  1. ghebaur

    Thread Starter Member

    Jun 17, 2014

    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.

    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


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

    Thread Starter Member

    Jun 17, 2014
    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
    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
    :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
    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.