AMT Encoder
AMT Encoder usually refers to the AMT series of rotary encoders made by CUI Devices / Same Sky.
These are used in robotics, CNC machines, motors, and automation systems to measure:
- Shaft position
- Rotation speed
- Direction
- Angular displacement
The AMT series is known for using capacitive sensing technology instead of traditional optical sensing.
What Makes AMT Encoders Special?
1. Capacitive Sensing
Unlike optical encoders, AMT encoders are:
- Resistant to dust, oil, and dirt
- More rugged in industrial environments
- Less sensitive to vibration
2. High Precision
They can provide very fine rotational measurements:
- Incremental outputs (A/B quadrature)
- Absolute position outputs
- Multi-turn tracking in some models
3. Programmable Resolution
Some AMT encoders allow configurable resolutions like:
- 48 PPR
- 1024 PPR
- 4096 PPR
Common AMT Encoder Types
| Type | Example | Purpose |
|---|---|---|
| Incremental Encoder | AMT10, AMT11, AMT12 | Measures relative movement |
| Absolute Encoder | AMT21, AMT22 | Gives exact shaft angle immediately after power-up |
| Commutation Encoder | AMT31, AMT33 | Used for BLDC motor commutation |
Example: Incremental AMT Encoder
An incremental AMT encoder outputs pulses as the shaft rotates.
If:
- Encoder = 1000 PPR
- Motor makes 1 revolution
Then the controller receives:
- 1000 pulses (or 4000 counts using quadrature)
Used for:
- PID speed control
- Odometry
- Servo feedback
- Robotics
Example: Absolute AMT Encoder
Absolute encoders know the shaft’s exact angle even after power loss.
Example:
- Shaft at 237°
- Power off
- Power on
- Encoder still reports 237°
Useful for:
- Robotic arms
- CNC axes
- Elevators
- Positioning systems
AMT21/22 models support multi-turn tracking too.
Typical Signals / Output
Depending on model:
- Quadrature A/B
- PWM
- SPI
- SSI
- RS-485
- U/V/W commutation signals
Applications
AMT encoders are commonly used in:
- Robotics
- BLDC motors
- Servo systems
- CNC machines
- Industrial automation
- AGVs and autonomous robots
It tells the controller:
- How far the motor turned
- How fast it’s spinning
- Which direction it moved
Additional Topics You Can Explore
- Incremental vs Absolute Encoders
- How AMT Encoders Work Internally
- Wiring Diagrams
- Arduino / ESP32 Interfacing
- Reading Encoder Signals in Code
- AMT vs Magnetic vs Optical Encoders
Technical Specifications
| Feature | Specification |
|---|---|
| Input Voltage | 3.3V to 5V DC |
| Operating Temp | -40°C to +125°C |
| Max Speed | Up to 7500 RPM |
| Technology | Capacitive ASIC |
| Bore Sizes | 2mm to 8mm (Adjustable) |
AMT Encoder Pinout (Standard 5-Pin)
Most AMT incremental encoders (like the AMT102 or AMT103) use a 5-pin connector. Here is the standard wiring:
- Pin 1 (B): Phase B Signal
- Pin 2 (5V): Input Power (3.3V - 5V)
- Pin 3 (A): Phase A Signal
- Pin 4 (GND): Ground
- Pin 5 (I): Index (Z-pulse) - Once per revolution
Interfacing with Arduino
To read an AMT encoder, use the Encoder.h library for the best performance. Below is a basic example using interrupts:
const int encoderPinA = 2;
const int encoderPinB = 3;
volatile long pulseCount = 0;
void setup() {
Serial.begin(9600);
pinMode(encoderPinA, INPUT_PULLUP);
attachInterrupt(digitalPinToInterrupt(encoderPinA), handleEncoder, RISING);
}
void loop() {
Serial.print("Position: ");
Serial.println(pulseCount);
delay(100);
}
void handleEncoder() {
pulseCount++;
}
AMT (Capacitive) vs. Optical Encoders
Why choose an AMT encoder over a traditional optical one?
- Durability: Optical encoders fail if the internal LED burns out or the disk gets dusty. AMT encoders are solid-state.
- Customization: One AMT encoder can often be adjusted to 16 different resolutions via DIP switches.
- Power Consumption: AMT encoders typically draw significantly less current (approx 6-10mA) than optical versions.
Frequently Asked Questions (FAQ)
Why am I getting "noisy" signals?
Capacitive encoders are resistant to dust, but they can be sensitive to electrical noise. Ensure you are using shielded cables and that the encoder ground is shared with your microcontroller ground.
Does the AMT10 series require a special tool for assembly?
No, one of the best features of the AMT series is the "One-Touch" assembly. They come with different sized sleeves (bushings) to fit various motor shaft diameters.
What is an Optical Encoder? (The Traditional Alternative)
Before capacitive technology (like AMT) became popular, Optical Encoders were the industry standard. They work using a very different physical principle:
- Light Source: An internal LED shines a beam of light.
- Code Disk: A glass or plastic disk with tiny slits rotates with the motor shaft.
- Photo-sensor: A sensor on the other side "sees" the light flickering through the slits.
The Main Weaknesses of Optical Encoders:
While very accurate, optical encoders have vulnerabilities that AMT encoders solve:
- Contamination: If a single speck of dust or drop of oil gets on the disk, the sensor can't "see" the light, causing errors.
- Fragility: The code disks are often made of glass, which can shatter during high-vibration or heavy-shock applications.
- LED Decay: Like any lightbulb, the internal LED gets dimmer over time (usually after 5–10 years), eventually leading to failure.
Internal vs. External Sensing: What does the Encoder do?
It is important to distinguish between how a robot "sees" the world and how it "feels" its own movement:
- External Sensors (LiDAR, Ultrasonic, Cameras): These help a robot find the speed and distance of other objects in its environment.
- Internal Sensors (AMT Encoders): These are used for the robot's own movement. They are attached directly to the motors to tell the robot exactly how far its own joints or wheels have turned.
Using AMT Encoders in Robotic Arms
In a robotic arm, every "joint" is powered by a motor. For the arm to pick up a delicate object, the controller needs to know the exact angle of every joint.
- Position Feedback: The encoder tells the controller if the arm is at 45° or 45.1°. This precision prevents the arm from crashing into things.
- Repeatability: Because AMT absolute encoders (like the AMT22) remember their position, the robotic arm can start working immediately when powered on without needing to "home" or calibrate itself.
- Smooth Motion: By measuring speed in real-time, the encoder helps the robot slow down gently before stopping, preventing "jerky" movements.
Using AMT Encoders for Distance (Odometry)
For mobile robots (like a Roomba or an industrial warehouse robot), encoders are used for Odometry.
By counting the pulses from the AMT encoder on the wheels, the robot's computer calculates:
Distance = (Total Pulses / Pulses Per Revolution) × Wheel Circumference
This allows the robot to know it has traveled exactly 5 meters and needs to turn left, even if it doesn't have GPS or cameras.
Optical Rotary Encoders vs VLC (Visible Light Communication)
1. Optical Rotary Encoders (Motion Control)
The "Optical Encoder" we discuss in robotics is an internal closed system. It doesn't "send" data through the air. The light stays inside the motor housing. Its only job is to tell a computer: "The motor just turned 1 degree."
2. VLC and Li-Fi (Data Communication)
What you may have seen regarding iPhone cameras and blinking LEDs in Japan is called Visible Light Communication (VLC) or Li-Fi.
- Purpose: To transfer files, internet data, or ID codes through the air.
- How it works: An LED blinks at ultra-high speeds (faster than the human eye can see). A camera or a photodiode receives these "blinks" as binary code (1s and 0s).
- The "Japan/iPhone" Tech: This is often called Optical Camera Communication (OCC). It uses the camera’s "rolling shutter" to detect patterns in light to download information from a smart LED bulb or a screen.
| Feature | Rotary Encoder (AMT/Optical) | VLC / Li-Fi |
|---|---|---|
| Primary Goal | Measure physical rotation/speed | Wireless data transfer (files/internet) |
| Data Source | A spinning disk or shaft | A digital file or network stream |
| Receiver | A fixed phototransistor | A camera sensor or specialized receiver |