Sindri Magnetic Rotary Encoder

What is this thing ?

This neat little piece of hardware was developed as a part of the Sindri light forging unit project. If the board looks familiar to you, you might have seen an early prototype on dangerous prototypes or hack a day last year.

We needed a rotary encoder that on the one hand has no mechanical parts that might wear out over time and on the other hand can resist a dusty workspace environment. Traditional optical encoders were either to expensive or to susceptible to dust and ambient light.

During our research we came across the AS5043 encoder chip by ASM. It uses a set of hal effect sensor and an integrated DSP to keep track of the rotation of magnet above the chip, with 10bit resolution. A SSI interface or an analogue output can be used to interface with an mcu. The magnet and the chip can even be separated by a layer of non magnetic material.

If you are interested in who we are, what we are doing, or simply our buildlog for this encoder, just head over to our wiki.

Features

• 10bit/0.35° Resolution (see our wiki oage on accuracy for details)
• SSI Interface (compatible to SPI in some ways)
• 0-5V Analogue output
• Status led that lights up on incorrect magnet aliment.

What exactly do I get for my money ?

As soon as this fundraiser is fully founded and the boards have been build, you'll get one PCB, with all the components soldered, except for the dual row pin header. It is included as well but not soldered, to make shipping cheaper and simpler.

Not included are any mechanical parts like screws, the magnets, the ball bearing or the chassis for holding everything in place. But fear not, we provide all the plans you need to build those yourself, using lathe or your 3D printer.

Where I can get the mechanical parts ?

Unfortunately providing the mechanical parts in larger quantities is too difficult and expensive. So you need to get them on your own.

The ball bearing is a rather common 6200Z bearing. You should be able to get one in a hardware store or on ebay.

For the magnet I'd recommend browsing ebay for 5mmx5mmx5mm neodym magnet cubes. Many shops offer 10 of them for 5$ or so.

Also you might need some M3 screws, to hold it all together.

For everything else we provide plans in two versions in our source code repo.

• The first version can be built using a lathe. Simply take the pdf files and show them to somebody who owns a lathe. He'll know what to do. Also you need some 5mm M3 distance bolts for this version.

• The second version can printed out on a 3D printer. Just grab the stl files and print them out on your favorite 3D printer. But be warned this version has not been tested yet.

Where can I get software for it ?

Of course we've also developped a library to interface with the AS5043 via SSI using a common ATmega microcontroller. The library can be found in our repository. This repo also contains a demo program for an ATmeg8 that sends measurements with 1° resolution out via the UART. If you connect your mcu to your Computer you can use the cube.py python script to visualize these measurements.

So okay what happens next ?

If this fundraiser is fully funded I'm going to order the boards on the parts. Be warned that due to shipping this alone can take up to 4 weeks. Then I'll probably need an other week to assemble and ship all the boards.

As long term goal I would like to turn this encoder in a product sold regularly on Tindie.

Of course I'm going keep you updated about the progress here.