[sdiy] Rotary Encoder Design

[Vladimir Pantelic]

see: https://ams.com/as5055a

they also offer the magnets for that application.

On Sat, Jul 25, 2020, 07:00 Ben Bradley <ben.pi.bradley at gmail.com> wrote:

> I thought up something a few years ago that may be useful for the
> currently-discussed sequencer, or really any synth device where you
> want to read several controls using high resolution with a
> microcontroller. I still haven't made a prototype, but there's no
> reason for this not to work.
>
> Background:
> Available rotary encoders are basically two types:
> 1. cheap detented mechanical (quadrature output, the whole four cycle
> output per detent) with 12 to 24 detents. These are used in car radio
> volume and tuning controls, and 90s CRT brightness-and-constrast
> controls. Often have a putbutton feature but that's not relevant here.
> The price on these is good, in the $1 to $2 range.
>
> 2. nice no-detent easy-turning shaft optical quadrature output with a
> few hundred counts per revolution. These are used for
> higher-resolution needs like (1990s) logic analyzers and digital
> oscilloscopes for the "master incremental controller." The prices I've
> seen on these are like $30, where you can barely justify one for a
> master controller. They give good resolution, but using several would
> be too costly to justify.
>
> My Idea:
> Use a couple of linear Hall-effect devices fixed at 90 degrees to each
> other, right behind a magnet on the end of the shaft encoder. These
> are arranged so that as the knob is turned through one rotation, one
> output would output one cycle of a sine wave, and the other would
> output one cycle of a cosine wave. Reading these in the A/D input of a
> microcontroller and doing the appropriate trig function (basically
> atan2) would give the angle of the shaft. You could (with appropriate
> multiplexing, etc.) read a large number of such encoders at what would
> feel like real time with a modern microcontroller. Even cheap plastic
> 3d-printable parts should get resolution to a couple degrees. Cost of
> parts might be $2 or $3 per encoder (not including microcontroller and
> multiplexing, which would be shared among the encoders).
>
> The parts I got for this a few years ago are TI DRV5053. It just
> occurred to me that perhaps similar are available with a digital
> interface, and looking on Digikey finds AS5510 with an I2C interface.
> These aren't necessarily optimal or the cheapest, just the first I ran
> across, but an I2C interface would be easier hardware-wise than
> multiplexing analog voltages.
>
> This doesn't cover displaying the value controlled by each encoder as
> it's turned, but that's a "separate function." For the
> currently-discussed sequencer you might only need to hear the
> oscillator for controlling pitch, and for duration use a two-digit
> display.
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