Android smartphone speedometer

Connecting reed switch to android smartphone, using minimum amount of components.

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Connecting reed switch to android smartphone, using minimum of components. You probably already have everything you need, but you may not be willing to use it ;)


final hardware working

MPEG-4 Video - 7.67 MB - 07/19/2018 at 09:42



hardware prototype working

MPEG-4 Video - 4.48 MB - 07/02/2018 at 18:25


  • 1 × android smartphone any android smartphone (you probably want root)
  • 1 × 4-pin headphone cable just cut open some headphones
  • 1 × 1M resistor probably can have other values, used as "dummy microphone"
  • 1 × reed switch I got mine from some cheap speedometer, if you have 3D printer or similar, you can print the "case" yourself
  • 1 × software something something Linux is not realtime enough? might need to try with a larger diameter wheel

  • Final Hardware

    Mis01207/19/2018 at 09:44 0 comments

    So, moving on from the prototype, this is the final hardware. Now it's only software missing ;)
    See video (in files)

  • Hardware Prototype

    Mis01207/02/2018 at 18:39 0 comments

    Cause I don't have a soldering iron near here, and cause I still don't know how I want to connect the reed switch (preferably using the original "connector", so I don't have to destroy a perfectly working thing (I had enough with the headphones), and cause the only 1M resistor I could find nearby is "prototyping only", I decided to just connect all the wires "somehow" and see if it all works together. And it does :)

    see the video for proof ;)

View all 2 project logs

  • 1
    wiring diagram
  • 2
    cut up some headphones with 4-pin plug

    If they have a mic+buttons box, you can pry it open and check if all 4 pins are connected. if they don't have a box, they're probably not.

  • 3
    obtain a reed switch

    My one is from a cheap  speedometer, so it's got a case and a magnet included.

View all 6 instructions

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