This library enables you to use 1 Hardware Timer on an ESP8266-based board to control up to 16 independent servo motors.

Why do we need this ISR-based Servo controller?

Imagine you have a system with a mission-critical function, controlling a robot arm or doing something much more important. You normally use a software timer to poll, or even place the function in loop(). But what if another function is blocking the loop() or setup().

So your function might not be executed, and the result would be disastrous.

You'd prefer to have your function called, no matter what happening with other functions (busy loop, bug, etc.).

The correct choice is to use a Hardware Timer with Interrupt to call your function.

These hardware timers, using interrupt, still work even if other functions are blocking. Moreover, they are much more precise (certainly depending on clock frequency accuracy) than other software timers using millis() or micros(). That's necessary if you need to measure some data requiring better accuracy.

Functions using normal software timers, relying on loop() and calling millis(), won't work if the loop() or setup() is blocked by certain operation. For example, certain function is blocking while it's connecting to WiFi or some services.

The catch is your function is now part of an ISR (Interrupt Service Routine), and must be lean / mean, and follow certain rules. More to read on:

https://www.arduino.cc/reference/en/language/functions/external-interrupts/attachinterrupt/

Important Notes:

1. Inside the attached function, delay() won’t work and the value returned by millis() will not increment. Serial data received while in the function may be lost. You should declare as volatile any variables that you modify within the attached function.

2. Typically global variables are used to pass data between an ISR and the main program. To make sure variables shared between an ISR and the main program are updated correctly, declare them as volatile.

It's better to use Arduino Library Manager to install this library.

Otherwise, you can install it using the following steps:

1. Navigate to (https://github.com/khoih-prog/ESP8266_ISR_Servo) page.
2. Download the latest release ESP8266_ISR_Servo-master.zip.
3. Extract the zip file to ESP8266_ISR_Servo-master directory
4. Copy whole folder to Arduino libraries' directory such as .Arduino/libraries/ESP8266_ISR_Servo-master.

The ESP8266 timers are badly designed, using only 23-bit counter along with maximum 256 prescaler. They're only better than UNO / Mega. The ESP8266 has two hardware timers, but timer0 has been used for WiFi and it's not advisable to use. Only timer1 is available. The timer1's 23-bit counter terribly can count only up to 8,388,607. So the timer1 maximum interval is very short. Using 256 prescaler, maximum timer1 interval is only 26.843542 seconds !!!

The timer1 counters can be configured to support automatic reload.

1. Add functions getPosition() and getPulseWidth()
2. Optimize the code
3. Add more complicated example

Now these new 16 ISR-based Servo controllers just use one ESP8266 Hardware Timer. The number 16 is just arbitrarily chosen, and depending on application, you can increase that number to 32, 48, etc. without problem. The accuracy is nearly perfect compared to software timers. The most important feature is they're ISR-based timers Therefore, their executions are not blocked by bad-behaving functions / tasks. This important feature is absolutely necessary for mission-critical tasks.

The MultipleServos example, which controls 6 servos independently, will demonstrate the nearly perfect accuracy. Being ISR-based servo controllers, their executions are not blocked by bad-behaving functions / tasks, such as connecting to WiFi, Internet and Blynk services.

This non-being-blocked important feature is absolutely necessary for mission-critical tasks. You'll see blynkTimer Software is blocked while system is connecting to WiFi / Internet / Blynk, as well as by blocking task in loop(), using delay() function as an example. The elapsed time then is very unaccurate

• ESP8266

How to use:

#define TIMER_INTERRUPT_DEBUG 1 #define ISR_SERVO_DEBUG 1 #include "ESP8266_ISR_Servo.h" // Published values for SG90 servos; adjust if needed #define MIN_MICROS 800 //544 #define MAX_MICROS 2450 int servoIndex1 = -1; int servoIndex2 = -1; void setup() { Serial.begin(115200); Serial.println("\nStarting"); servoIndex1 = ISR_Servo.setupServo(D8, MIN_MICROS, MAX_MICROS); servoIndex2 = ISR_Servo.setupServo(D7, MIN_MICROS, MAX_MICROS); if (servoIndex1 != -1) Serial.println("Setup Servo1 OK"); else Serial.println("Setup Servo1 failed"); if (servoIndex2 != -1) Serial.println("Setup Servo2 OK"); else Serial.println("Setup Servo2 failed"); } void loop() { int position; if ( ( servoIndex1 != -1) && ( servoIndex2 != -1) ) { for (position = 0; position <= 180; position++) { // goes from 0 degrees to 180 degrees // in steps of 1 degree ISR_Servo.setPosition(servoIndex1, position); ISR_Servo.setPosition(servoIndex2, 180 - position); // waits 50ms for the servo to reach the position delay(50 /*15*/); } for (position = 180; position >= 0; position--) { // goes from 180 degrees to 0 degrees ISR_Servo.setPosition(servoIndex1, position); ISR_Servo.setPosition(servoIndex2, 180 - position); // waits 50ms for the servo to reach the position delay(50 /*15*/); } } } 

1. Search for bug and improvement.
2. Similar features for Arduino (UNO, Mega, etc...) and ESP32

1. Add example using [Blynk] (http://docs.blynk.cc/) to control servos. Change example names to avoid duplication.

1. Basic 16 ISR-based servo controllers using 1 hardware timer for ESP8266.

If you want to contribute to this project:

• Report bugs and errors
• Ask for enhancements
• Create issues and pull requests
• Tell other people about this library

Copyright 2019- Khoi Hoang