Technology
How To: DIY quadrature encoder

This might be just the thing for a robotics project cancelled on account of – “expensive”. Professor Mason created a quadrature encoder by fitting a motor with 2 inexpensive hall-effect sensors and a small magnet –

In this application, two sensors are attached 90 degrees out of phase around the motor. A small permanent magnet is attached to the motor shaft. Each of the sensors is fed to an ADC on a picaxe 08M.
[…]
As per standard quadrature encoders, the leading pulse tells us the direction of the rotation while the number of pulses tells us the distance rotated. For example, here is a pulse train for the encoder rotating the opposite way.

If you’re not familiar with rotary encoders building one is (of course) a fantastic way to learn – encoders or ‘angle transducers’ come in handy for determining the position of a control knob or robotic appendage, among others things. [via Ladyada’s Ranting]

3 thoughts on “How To: DIY quadrature encoder

  1. This is an old technique for equipment monitoring, and brushless fans.

    You forget to account for those sensors’ metal legs slowly magnetizing over time (in addition to the drive).

    Also note this change in the analog signal is nonlinear with respect to position… so a comparator will not fix your problem.

    Although it will not be reliable for angles etc. it should work for calculating direction, rotations, and velocity.

    You may disagree and think I am wrong… for awhile…
    =P

    If you cite the design source then perhaps someone will tell you how to fix it so it will last.

    Spoiler… add another magnet to the other side of the shaft with an opposing poll facing outwards.

  2. This is an old technique for equipment monitoring, and brushless fans.

    You forget to account for those sensors’ metal legs slowly magnetizing over time (in addition to the drive).

    Also note this change in the analog signal is nonlinear with respect to position… so a comparator will not fix your problem.

    Although it will not be reliable for angles etc. it should work for calculating direction, rotations, and velocity.

    You may disagree and think I am wrong… for awhile…
    =P

    If you cite the design source then perhaps someone will tell you how to fix it so it will last.

    Spoiler… add another magnet to the other side of the shaft with an opposing poll facing outwards.

  3. While a great idea and an interesting solution, I’d be worried about the “jitter” caused by an unbalanced motor shaft.

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