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What is the best yet simple to use angular position sensor? I am building a robotic hand and I want to implement this sensor at the joints of the fingers. I don't need a module, just an analogue output. Thank you.

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  • $\begingroup$ Please be more specific. Questions like these are very broad and "best" is a very subjective term. $\endgroup$ – Shahbaz Dec 12 '14 at 12:42
  • $\begingroup$ Some servos have sensors that tell where they are pivoted to. This is part of what makes them so effective. if you place servos in the joints as motivators, you can double them as sensors. $\endgroup$ – Vince Scalia Dec 12 '14 at 18:16
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Another popular rotary sensor is the ratiometric Hall effect sensor.

Use a device like the A1324. It's a 3-pin device which gives an analog voltage proportional to the magnetic field strength. For a magnet, you have two options:

  • A diametrically polarised ring magnet mounted on the steering column. The sensor should sit at the circumference of the magnet, facing the centre.
  • An axially polarised button magnet. Mount it on the steering column with its diameter colinear with the rotation axis.

Hall effect sensors

As the magnet rotates, the output of the sensor changes sinusoidally. If you get the strength of the magnet just right, you can have very nearly a 5v output swing. However, since the output is sinusoidal, you won't be able to measure more than about 120º with good resolution.

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Potentiometers are great for this kind of thing. Its what servos use to move to specific angles. They offer a linear resistance change that could be used to change an analog voltage that you measure, then angles map directly to that voltage.

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  • A potentiometer linked to the output gear of your motor controlling the joint is the simplest position sensor. This is typically what is done inside cheap servomotors.

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You will get an analog signal relative to the position of the output gear. Position can be found using the relation

$$\theta = \theta_0 + \frac{V_{out}}{V_{max}}$$

With $V_{max}$ the maximum voltage at the potentiometer end, $\theta_0$ the initial position. Precision depends on the quality of the potentiometer.

  • Magnetic encoder is a bit more complicated, but more precise. Magnetic encoder IC allow you to get position regarding the magnetic field induced by a magnet fixed to your joint. Precision usually is of 2000 tics per joint turn. Check out this project for example.
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Probably a simple and cost-effective solution would be to use a flex sensor. Essentially you can determine the amount of flex subjected on the sensor using resistance, much like a potentiometer.

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