Hall Effect switch

jacky February 26, 2010 8 Comments

The circuit diagram shown here is of a Hall Effect switch. Hall Effect sensor IC DN6848 from Panasonic is the heart of the circuit. The DN6848 has a built-in Hall Effect sensor, Schmitt trigger circuit, power supply regulator and temperature compensation circuits integrated to a single chip. High sensitivity, low drift and excellent temperature stability of the DN6848 makes it well suitable for a variety of position, rotation and speed sensing applications.
When the south pole of a magnet is brought near to the front face (face with type number marking) of the IC its output pin (pin 3) goes low (zero voltage).The pin 3 is connected to the base of PNP transistor Q1 and the low stage at pin3 makes the transistor ON and makes the relay activated. In a nut shell the relay will get switched ON whenever the south pole of a magnet is brought close to the Hall Effect sensor IC DN6848. Resistor R1 will always pull the base of Q1 to a very slight positive voltage and thereby prevents accidental triggering. LED D1 glows whenever the relay is activated and resistor R2 limits the current through the D1. Diode D2 is a freewheeling diode and it protects the transistor Q1 from high voltage spikes which are induced when the relay is switched.
Circuit diagram.

hall effect switch


  • The circuit can be assembled on a perf board.
  • The relay K1 can be a 5V SPDT relay.
  • Use 6V DC for powering the circuit.
  • The wattage of the device that can be switched depends on the capacity of the relay.
  • dave
    July 22, 2014

    hall trigger does the magnet have to pass completly over the trigger,ie my application is motor cycle gear change;its having trouble finding 2nd gear on the digy read out,it finds 2nd on the 3rd gear change,dave

  • December 17, 2012

    Hello i have IC DN6838 can u help me please can i use it and what relay should i use for it. plz reply

  • seetharaman
    June 18, 2010

    Hi Pitong Thanks you are correct it should be D2.

    Hi Art Thanks you are correct 2N2907 is a PNP transistor, collector and emitter should be interchanged and should be shown as PNP transistor, relay in emitter circuit.

  • Art
    June 17, 2010

    Sorry, I may be missing something, but to me it looks like the transistor is incorrectly placed. I’m sure that the emitter and collector should be the other way around?

  • pitong
    February 27, 2010

    from the circuit description-“D2 was mentioned but in the schematic diagram,there is is no D2 but D3.maybe, clerical error!

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