Magnetic angle sensors

A magnetic angle sensor is a contactless electronic device used to measure the rotational position of a shaft or object. It works by detecting the orientation of a magnetic field—usually from a small permanent magnet attached to the rotating part—and converting that physical position into a digital or analog signal.

How It Works

• The Magnet: A simple dipole (North/South) magnet is mounted on the end or side of a rotating shaft.
• The Sensing Element: An integrated circuit (IC) is placed close to the magnet. It uses physical phenomena such as the Hall Effect and magnetoresistance (AMR/GMR/TMR) to detect the direction of magnetic flux lines.
• The Processor: The sensor’s internal logic calculates the precise angle (0° to 360°) based on the field strength across multiple internal axes and outputs that data via interfaces like SPI, I²C, or PWM.

Technical Comparison of Several Typical Magnetic Angle Sensors

Key Product Highlights

• ams OSRAM AS5047P: Noted by experts for its Dynamic Angle Error Compensation (DAEC), which maintains accuracy even at 28,000 RPM.
• ams OSRAM AS5600: A popular, low-cost choice for contactless potentiometers and battery-powered devices due to its simple I2C interface and low power modes.
• MagnTek MT6701: Often cited as a superior AS5600 replacement; it offers higher 14-bit resolution and much higher speed support (55k RPM) while remaining affordable.
• MagnTek MT6835: A high-performance 21-bit sensor that delivers over 2 million steps per revolution, making it ideal for micro-level accuracy in professional robotics.
• Infineon TLE5012B: Praised for its robustness in extreme environments (-40°C to +150°C) and stable readings under high heat.

• Hall Effect Sensors: The most widely used type. According to Allegro MicroSystems, these are often integrated into single-chip CMOS solutions like the Allegro A33002, making them cost-effective for general motor control and automotive steering.
• Anisotropic Magnetoresistance (AMR): These sensors, such as the Honeywell HMC1501, are prized for high precision. A key limitation noted by Infineon is that a standard AMR element is unique only over a 180° range, often requiring additional logic or sensors to achieve full 360° detection.
• Giant Magnetoresistance (GMR): Based on multi-layer thin films, GMR sensors like the Infineon TLE5012B offer a much higher signal-to-noise ratio than Hall sensors. Experts at Alif Sensor highlight that GMR was a Nobel Prize-winning discovery that allowed for extreme miniaturization.
• Tunnel Magnetoresistance (TMR): The newest and most advanced type. TDK-Micronas states that TMR sensors (e.g., the TDK TAD2141) provide 500 times the output of a Hall element while consuming significantly less power, making them ideal for battery-operated and high-reliability automotive systems.

The MagnTek MT6816 is a high-speed, 14-bit magnetic angle sensor IC based on advanced Anisotropic Magnetoresistive (AMR) technology. It is specifically designed to provide absolute 0°–360° angle sensing for high-performance applications like BLDC motor control and robotics.

Core Technical Specifications

According to official technical documents from MagnTek and Novosense, the sensor features the following primary specifications:

• Resolution: 14-bit absolute angle resolution (16,384 steps per revolution).
• Maximum Speed: Supports rotation speeds up to 25,000 RPM.
• System Latency: Ultra-low propagation delay of less than 2 µs.
• Operating Voltage: 3.0V to 5.5V DC.
• Supply Current: Typically 10mA.
• Operating Temperature: Industrial range from -40°C to +125°C.
• Magnetic Flux Density: Operates within a range of 30 mT to 1,000 mT.

MT-6816 Pinout

Pin Functionality by Mode

The output pins (Pins 5 and 6) and the SPI pins change behavior based on your interface choice:

• SPI Mode: Uses Pins 1-4 for data transfer. It supports both 3-wire (sharing SDI/SDO) and 4-wire configurations.
• Incremental Mode (ABZ): Pin 6 provides the Z (Index) pulse, while internal programming determines which pins output the A and B quadrature signals (often multiplexed on the SPI lines when SPI is not active).
• Motor Commutation (UVW): Pin 6 provides the W phase, replacing traditional Hall effect sensor signals for brushless motors.

Connection Notes

• Power Supply: Place a 0.1µF decoupling capacitor as close as possible between VDD (Pin 8) and VSS (Pin 7) to ensure stable readings.
• Magnet Placement: The magnet should be centered over the SOP-8 package's geometric center for maximum accuracy.
• SPI Settings: For microcontroller communication, use SPI Mode 3 (CPOL=1, CPHA=1) with MSB first.

Arduino example

To read the 14-bit absolute angle from the MagnTek MT6816 using an Arduino, you use the SPI interface. The sensor requires SPI Mode 3 (CPOL=1, CPHA=1) and a clock speed up to 16MHz.

Arduino Wiring

Connect the MT6816 to your Arduino (e.g., Uno/Nano) as follows:

• VDD (Pin 8) → 3.3V or 5V
• VSS (Pin 7) → GND
• CSN (Pin 1) → D10 (Chip Select)
• SCK (Pin 2) → D13 (Serial Clock)
• SDO (Pin 3) → D12 (MISO)
• SDI (Pin 4) → D11 (MOSI)

Example Sketch

This code initializes the SPI bus and reads the absolute angle from registers 0x03 and 0x04

#include <SPI.h>
 
const int CS_PIN = 10;
const byte READ_REG_03 = 0x83; // Read command for Register 0x03
 
void setup() {
  Serial.begin(115200);
  pinMode(CS_PIN, OUTPUT);
  digitalWrite(CS_PIN, HIGH);
 
  SPI.begin();
}
 
void loop() {
  uint16_t angle = readMT6816();
 
  // Convert 14-bit raw value (0-16383) to degrees (0-360)
  float degrees = (angle * 360.0) / 16384.0;
 
  Serial.print("Raw: ");
  Serial.print(angle);
  Serial.print(" | Angle: ");
  Serial.println(degrees);
 
  delay(100);
}
 
uint16_t readMT6816() {
  // MT6816 requires SPI Mode 3, MSB first, max 16MHz
  SPI.beginTransaction(SPISettings(10000000, MSBFIRST, SPI_MODE3));
 
  digitalWrite(CS_PIN, LOW);
 
  // Step 1: Send read command for the first register
  SPI.transfer(READ_REG_03);
 
  // Step 2: Read two bytes
  uint8_t highByte = SPI.transfer(0x00);
  uint8_t lowByte = SPI.transfer(0x00);
 
  digitalWrite(CS_PIN, HIGH);
  SPI.endTransaction();
 
  // Combine bytes: The 14-bit angle is in highByte and bits [7:2] of lowByte
  uint16_t rawData = (highByte << 8) | lowByte;
  uint16_t angle = (rawData & 0x3FFF); // Mask to 14 bits
 
  return angle;
}

Key Coding Details

• Register Access: The absolute angle data is stored in registers 0x03 and 0x04. Sending 0x83 (Read bit + address 0x03) allows you to burst-read both bytes.
• Data Masking: The sensor provides 14-bit data. The result must be masked with 0x3FFF to remove any parity or error flags stored in the remaining bits.
• Parity Check (Optional): For high-reliability applications, you can verify the parity bit (typically bit 15) to ensure the data wasn't corrupted during transmission.

The MagnTek MT6835 is a fourth-generation magnetic angle encoder IC that significantly improves upon the MT6816, offering higher resolution and specialized calibration features. Based on Anisotropic Magnetoresistive (AMR) technology, it is designed for ultra-high-precision applications such as absolute-value servo motor control and high-speed robotics.

Technical Specifications

According to data from MagnTek and Novosense, the MT6835 features the following core parameters:

• Resolution: 21-bit absolute angle resolution (over 2 million steps per revolution).
• Maximum Speed: Supports high-speed rotation up to 120,000 RPM.
• Accuracy (INL):
  • Factory Default: < ±0.5°.
  • After Self-Calibration: Typical accuracy of ±0.07°.
  • With NLC Mode: Typical accuracy of ±0.02°.
• System Latency: 2 µs to 10 µs propagation delay.
• Operating Voltage: 3.0V to 5.5V DC (3.3V to 5.0V typical).
• Operating Temperature: Industrial range from -40°C to +125°C.

Output Interfaces

The MT6835 provides several independent output modes, making it a versatile replacement for optical encoders:

• SPI: Standard 4-wire interface supporting up to 16 MHz clock frequency for reading 21-bit angle data.
• Incremental ABZ: Programmable resolution from 1 to 16,384 lines (pulses per revolution).
• Incremental UVW: Supports any resolution from 1 to 16 pole pairs.
• PWM: 12-bit absolute angle output.

MT6835 Pinout

Key Hardware Considerations

• Decoupling: It is critical to place a 100 nF (0.1 µF) capacitor between VDD (Pin 13) and VSS (Pin 4), and another capacitor on the VOUT (Pin 14) pin, for internal voltage stability.
• Calibration Pin: Pin 1 (CAL) can be used to trigger the built-in self-calibration routine, which is unique to the MT6835 and improves its accuracy to ±0.07°.
• Independent Outputs: Unlike the MT6816, which often shares pins, the MT6835 allows you to use SPI and ABZ/UVW outputs simultaneously without pin multiplexing conflicts.

MT-6835 Arduino example code

To read the 21-bit absolute angle from the MT6835, you must use the SPI interface. Because 21 bits exceed a standard 16-bit integer, you will need to store the data in a uint32_t.

Wiring (MT-6835 to Arduino)

• VDD (Pin 13) → 3.3V or 5V
• VSS (Pin 4) → GND
• CSN (Pin 12) → D10
• SCK (Pin 11) → D13
• MISO (Pin 9) → D12
• MOSI (Pin 10) → D11

Example code

The MT6835 stores its 21-bit angle across three registers starting at 0x03.

#include <SPI.h>
 
const int CS_PIN = 10;
const byte READ_CMD = 0x83; // Read bit (0x80) + Register address (0x03)
 
void setup() {
  Serial.begin(115200);
  pinMode(CS_PIN, OUTPUT);
  digitalWrite(CS_PIN, HIGH);
 
  SPI.begin();
}
 
void loop() {
  uint32_t rawAngle = readMT6835();
 
  // Convert 21-bit (0 to 2,097,151) to degrees
  float degrees = (rawAngle * 360.0) / 2097152.0;
 
  Serial.print("21-bit Raw: ");
  Serial.print(rawAngle);
  Serial.print(" | Angle: ");
  Serial.println(degrees, 4); // 4 decimal places for precision
 
  delay(50);
}
 
uint32_t readMT6835() {
  // MT6835 SPI: Mode 3, MSB first, up to 16MHz
  SPI.beginTransaction(SPISettings(8000000, MSBFIRST, SPI_MODE3));
  digitalWrite(CS_PIN, LOW);
 
  SPI.transfer(READ_CMD);
  uint32_t b1 = SPI.transfer(0x00); // Bits 20-13
  uint32_t b2 = SPI.transfer(0x00); // Bits 12-5
  uint32_t b3 = SPI.transfer(0x00); // Bits 4-0 + Status bits
 
  digitalWrite(CS_PIN, HIGH);
  SPI.endTransaction();
 
  // Combine the bytes:
  // The 21-bit angle is packed into the 24 bits of data returned.
  // Format: [Byte1: 8 bits][Byte2: 8 bits][Byte3: 5 bits + 3 status bits]
  uint32_t combined = (b1 << 16) | (b2 << 8) | b3;
  uint32_t angle = combined >> 3; // Shift right by 3 to remove status bits
 
  return angle;
}

Critical Implementation Details

• Bit Packing: The sensor returns 3 bytes (24 bits). The top 21 bits are the angle, while the bottom 3 bits are status flags (like No-Magnet or Over-speed errors).
• SPI Mode: Like its predecessor, the MT6835 uses SPI Mode 3. If you get oscillating or “garbage” data, double-check your CPOL/CPHA settings.
• High Resolution: Because 21-bit resolution is extremely sensitive (0.00017° per step), even tiny vibrations or magnetic noise will cause the last few digits to flicker.

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