Servo Input Library

This is an Arduino library that allows you to read the position of servo motors via their signal wire without delay. You can use this library to read RC receiver channels, find the motor positions of robotics, or debug other servo motor projects.

For more information, see the article and tutorial on PartsNotIncluded.com.

Getting Started

#include <ServoInput.h>

ServoInputPin<2> servo;

void setup() {
	servo.attach();
}

void loop() {
	float angle = servo.getAngle();  // get angle of servo (0 - 180)
}

Connecting Servos

Servo motors are driven by three pins: signal, power, and ground. To use this library, each 'signal' pin needs to be connected to an interrupt-capable I/O pin and the servo's ground wire must be tied to the Arduino's GND pin.

Signals and Interrupts

The Servo Input library uses external interrupts to keep track of servo positions without delaying the rest of your sketch. In order for the library to work, you must connect the servo signal wires to interrupt-capable pins.

BOARD	DIGITAL PINS USABLE FOR INTERRUPTS
Uno, Nano, Mini, other 328-based	2, 3
Uno WiFi Rev.2	all digital pins
Mega, Mega2560, MegaADK	2, 3, 18, 19, 20, 21
Micro, Leonardo, other 32u4-based	0, 1, 2, 3, 7
Zero	all digital pins, except 4
MKR Family boards	0, 1, 4, 5, 6, 7, 8, 9, A1, A2
Nano 33 IoT	2, 3, 9, 10, 11, 13, A1, A5, A7
Nano 33 BLE, Nano 33 BLE Sense	all pins
Due	all digital pins
101	2, 5, 7, 8, 10, 11, 12, 13

^{Original table from arduino.cc/reference, modified to show only CHANGE interrupts}

Some third party boards such as the Teensy 3.2 and the ESP8266 support external interrupts on all pins. Be sure to check the documentation for your board before connecting your servos.

Each servo's signal wire needs to be connected to a separate pin. If you do not have enough interrupt-capable pins on your board, you can also use pin change interrupts. ServoInput integrates with NicoHood's PinChangeInterrupt library for AVRs - just import Nico's library before ServoInput and any necessary pin change interrupts will be added automatically. Be aware that due to the extra overhead pin change interrupts are not as accurate or reliable as external interrupts. Keep that in mind when choosing which pins to connect to which servo.

Power Levels

Often servo motors are driven at higher voltages than your Arduino can handle. In this case, you will need either a level shifter or a voltage divider for the signal wire. Use a multimeter to check the servo's voltage level before making your connections.

Warning: if the servo's voltage is above the acceptable voltage for the Arduino, connecting the signal wire directly risks permanently damaging the board. Be smart and check before you connect anything.

Common Ground

If your servo is not powered by the Arduino running ServoInput, you must connect the ground wire from the servo's power supply to the ground pin of the Arduino so that they share a common reference.

If you are measuring multiple servos that use the same power supply, you do not need to connect the ground wire for each servo. Just the one is fine.

License

This library is licensed under the terms of the GNU Lesser General Public License (LGPL), either version 3 of the License, or (at your option) any later version.