This instructable explains how to measure shaft angles using an AS5600 magnetic encoder and an Arduino UNO R3 microcontroller.

Multi-turn (total-angle) measurements are supported.

The AS5600 is capable of 12-bits resolution which equates to 360/4096=0.087 degrees. This resolution assumes ideal magnet positioning and no distortion of the magnetic field. In practice I observed variations of up to 2 degrees which can be reduced using interpolation.

A method for reducing these errors to less than 0.5 degrees is explained.

The STL files for the test-jig sensor-mounting bracket and magnet-adapter are included.

The cost of the AS5600 sensor module, magnet, and I2C level converter is less than $5.00

Images

Photo 1 (cover) shows the magnetic encoder attached to a NEMA17 stepping motor
Photo 2 shows the rear view of the encoder
Photo 3 shows the calibration test jig
The video shows the encoder in operation

Supplies

The following items were obtained from https://www.aliexpress.com/

1 only AS5600 encoder complete with diamagnetic magnet
1 only I2C logic level convertor
1 only Arduino UNO R3 complete with USB cable
1 only Big Easy Driver motor controller
1 only NEMA17 17HS3430 stepping motor
1 only NEMA17 mounting bracket

The following items were on hand

Arduino jumper wires
4 only M3 x 9mm threaded nylon spacers
8 only M3 x 5mm bolts
4 only M3 x 10mm bolts
2 only M3 nuts
4 only M4 x 10mm bolts
2 only M4 nuts

The cost of the AS5600 sensor module, magnet, and I2C level converter was less than $5.00

Step 1: Theory

Magnetic encoder chips contain two (or more) Hall sensors at right angles to each other. [1]

The construction of a hall sensor is such that an output voltage appears whenever a semicoductor channel experiences a perpendicular magnetic field.

The amplitude of this voltage decreases to zero when the magnetic field is edge-on.

Reversing the magnetic field reverses the voltage.

Rotating a Hall sensor within a constant magnetic field produces a sinusoidal output.

We get the following outputs if we orientate two sensors at 90 degrees to each other.

Sensor1 = I = sin(A) ……….………………..............……. (1)

Sensor2 = Q = sin(A + 90) …..…………………................. (2)

Where

A is the angle of the Hall sensor with respect to the magnetic field
I is the in-phase output
Q is the quadrature (90 degree) output

Expanding (2)

Sensor2 = Q = sin(A)*cos(90) + cos(A)*sin(90)

= sin(A)*0 + cos(A)* 1

Sensor2 = Q = cos(A) ………………….......................... (3)

Divide (3) into (1)

sin(A)/cos(A) = tan(A) ………………….................……... (4)

We can now calculate angle A

angle A =atan2(Q, I) ………………………............…..…...(5)

Note

[1]

It is possible to make your own magnetic encoder by mounting two linear Hall sensors at right-angles to each other.

Photo 1 shows the Arduino ADC (analog-to-digital) readings for two 49E sensors mounted at right-angles. Note that the mid-point of each sinewave is approximately ADCmax/2 = 1023/2 = 512.

Integrated circuits, however, are preferrable because the sensors can be placed closer together, and are precisely aligned, which results in higher precision.

Step 2: Circuits

Photo 1 shows how to connect the AS5600 magnetic encoder to your Arduino Uno R3

The I2C level shifter is not required when using a 3.3 volt microcontroller.

Photo 2 shows how to connect the Big Easy Driver and motor to your Arduino R3.

Step 3: STL Files

The following STL files are attached to this step:

Photo 1 … “ AS5600_magnet_mount.stl”
Photo 2 … “AS5600_pcb_mount.stl”

Step 4: Assembly

Magnet mount

Replace the grub-screws in a GT2-20 timing pulley with M4 bolts (I cut mine down)
Attach the magnet mount to the GT2-20 timing pulley as shown in photo 1.
Press the diametric magnet that is supplied with each AS5600 breakout board into the hole at the end of the 3D magnet mount.

PCB mount

Attach the PCB to the PCB mount with two M3 x 10mm nuts and bolts as shown in photo 2
Attach the PCB mount to the NEMA17 stepping motor with two M3 x 10 nuts and bolts

Adjust the magnet distance

Loosen the GT2-20 grub-screws and slide the timing pulley back/forth for a 2..3mm gap between the face of the magnet and the AS5600 sensor chip.

Step 5: Software

Installation

Download the attached code “AS5600_interpolation.ino” [1]
Copy the contents into a new Arduino sketch and save the sketch as “AS5600_interpolation” (without the quotes). Use a text editor such as Notepad++ …nota word processor
Now compile and upload the sketch to your Arduino
Done …

Run the software

Apply 12 volts to the motor
Adjust the motor current limit on the Big Easy Driver motor controller to 400 milliamps (0.4 amps) using the current-limit potentiometer on the Big Easy Driver
Open your Ardiono IDE (Integrated Development Environment) and left-click “Tools | Serial Monitor” and set the “baud speed” to 115200.
The motor should turn and measurements scroll down the screen each time you click “Tools | Serial Monitor”
The calibration values are the first set of readings taken at 9 degree intervals. [2]

Notes

[1]

Code

The AS5600 code is from https://curiousscientist.tech/blog/as5600-magnetic-encoder-a-practical-example
The motor control code is a modified version of my https://www.instructables.com/4-Wire-Horizontal-Plotter/
The interpolation algorithm is mine.

[2]

Providing your project has a home position (i.e. the motor always starts from the same position) the calibration values can be permanently written into the header array.

AS5600_interpolation.ino
Download

Step 6: Error Correction

The graph in photo1 shows the measured and corrected angles for my AS5600 magnetic encoder.

A calibration table was created by rotating the magnet at 9 degree intervals and recording the sensor values into an array[]. These values are shown in the attached file “AS5600 Error Correction. txt” along with measurements taken every 50 micro-steps [1]

Let’s correct the reading of 176.04 degrees we measured at 1550 motor (micro) steps.

The Actual Value

The actual angle at 1550 microsteps is 1550/3200*360 = 174.38 degrees

The measured error is therefore 176.04 – 174.38 = 1.66 degrees …………………….. (1)

The Interpolated Value

The measured reading of 176.04 lies between the following values in our calibration table

array[19] = 172.72

array[20] = 182.11

Since the array readings are 9 degrees apart the interpolated value is

Interpolated value = index-of-array[19] * 9 + (measured – array[19])/(array[20] – array[19]) * 9

= 19 * 9 + (176.04 – 172.72) / (182.11 - 172.72) * 9

= 171 + 3.33 / 9.39 * 9

= 171 + 3.19

= 174.19 degrees

The interpolatederror is therefore 174.38 – 174.19 = 0.18 degrees …………………. (2)

Photo 1 shows the corrected readings in red [2]

Notes

[1]

A NEMA17 motor requires 200 steps/revolution or 1.8 degrees/step

With 16x micro-stepping each revolution takes 200*16 = 3200 micro-steps

[2]

This error-correction technique can be used with any sensor.

AS6800 Error Correction.txt
Download

Step 7: Summary

This instructable explains how to measure a rotational angle of a motor shaft using an AS5600 magnetic encoder and an Arduino UNO R3 microcontroller.

The software supports multi-turm (total-angle) measurements

The AS5600 is capable of 12-bit resolution which equates to 360/4096=0.087 degrees.

This resolution assumes ideal magnet positioning and no distortion of the magnetic field. In practice variations of up to 2 degrees have been observed.

An interpolation algorithm for significantly reducing these errors is explained.

Click here to view my other instructables.