Help needed with Hall effect sensor

Discussion in 'Automotive Electronics' started by setsquar, Oct 8, 2018.

  1. setsquar

    Thread Starter Active Member

    Oct 11, 2012
    34
    4
    Below is a schematic of a points assisted electronic ignition
    what I would like to do is use a Hall sensor to replace the points
    what I would like to know is a pull up resistor needed
    the output of the Hall is 20mA is this enough to fully turn on the transistor
    and what Tr would be best to use
    do I need to add any other resistors anywhere
    Hall sensor is a TLE4906LHALA1
    as always thanks for your help

    cb2Hall.jpg cb2Hall.jpg img006.jpg
     
  2. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
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    You don't need a pull up with this circuit , i have made the vellemen kit for a motorbike, and used a hall effect sensor, i put the output across the middle of the two diodes D1,D2, it works ok, note when the magnet is present, the coil fires,

    I chose one with a higher output current A3144 type@25mA.
     
    Last edited: Oct 9, 2018
  3. wayneh

    Expert

    Sep 9, 2010
    14,790
    5,277
    In my opinion you want the output of the hall switch to replace the "output" of the points, leaving R1-R3 and D1 and D2 unaltered. The hall switch is an open collector output that connects the output to ground when "on". That's exactly what the points did. But unlike @Dodgydave, I have no experience with this and have based my answer on the data sheet.
     
  4. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
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    If you put the hall effect sensor across the input of the kit, it's giving 80mA through R1,R2 which is too much for the sensor, that's why i put it between the diodes, otherwise you need a slave pnp transistor like a 2N4403.
     
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  5. setsquar

    Thread Starter Active Member

    Oct 11, 2012
    34
    4
    the circuit is potted and boxed up and in use so I have to use the existing points wire that goes to the R1-R3 junction
    I now see the need for a PNP transistor I have
    TIP32A, BD202, and RN4919 could I use any of these
    seems I will need a resistor from base to collector to keep it on until the Hall turns it off what sort of value will I need
    thanks for your help
     
  6. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
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    You just need to put the output of your hall effect sensor to the base of the Tip32A a 1K resistor to Positive pullup, and put the Emitter to the points input, Collector to gnd,.

    Note that the sensor should be closed with No Magnet Present,(points closed not firing) if your sensor is reversed, ie closed with the magnet, then you need a NPN TIP31A transistor, Emitter to gnd, Collector to points input.
     
    Last edited: Oct 9, 2018
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  7. setsquar

    Thread Starter Active Member

    Oct 11, 2012
    34
    4
    Ok im I being stupid
    PNP needs base and collector low,negative to be on (T1 on T2 off)
    and base positive to turn off (T1 off T2 on)
    or does the Hall switch do that as much as I have read about them still not sure exactly how the operate
     
  8. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
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    Correct,, here is a drawing to help..

    Your sensor needs the magnet to be closed, so you need a NPN, this means that the coil will Fire when the magnet is present.

    DSC_0172.JPG
     
    Last edited: Oct 9, 2018
    quebecspring likes this.
  9. setsquar

    Thread Starter Active Member

    Oct 11, 2012
    34
    4
    Much to my surprise it works
    thanks for your help:)
     
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