Activating Servos Simultaneously

Hi Remo,

Since you are dealing with a single processor there is no way for it to do 2 things simultaneously. One option would be to have a separate processor for each servo or you could trigger and latch a driver circuit to actually move the servo. If it is important for the servos to operate simultaneously you could use the enable on the driver to delay the start of the first servo until the second one is activated. I do not know exactly what you are doing and the fact of the matter is that there are other guys on the forum who have better knowledge than me. Your question interests me so I will continue to follow this thread.

John

Hi Remo,

As John says, typically expect one processor to do one thing at a time. There are methods to make it appear that multiple things are occurring at the same time, but you need to structure your code entirely differently to do that (using timer 'ticks') or to make use of an operating system which will make it transparent to your user code. This is all a massive subject so I can't explain all in the space of a discussion response. To see what you need to research and read up on, and to get a hint on some ways you might achieve it, see here:

Multiple Arduino functions without delay

The real problem is the delay. This is deadly in multiple events like you want. I will point at a possible process that you need to understand. If I go to sleep for ten hours, I am not conscious of anything ( delay(10) ). But it a setup an alarm clock say every hour( delay(1) ), I can check something before going to sleep another hour until 10 hours are finished. But realize, on average things will wait about 30 minutes before I get around to it.

Clem

So everyone is saying the right words but to help you categorically (But you will still have to read and learn as im not giving you a direct solution )

https://www.arduino.cc/en/Tutorial/BlinkWithoutDelay

This explains how to do it with an example, try it out, see how it works and im sure you may have other questions but is will show yo what everyone is hinting at

Regards

Peter

Well you can't do it with arduino but there are other microcontrollers which are capable of performing such tasks i.e. have multitasking capabilities with less coding. For example: check this :XK-STK-A8DEV XK-STK-A8DEV

It's a basic development kit by XMOS i.e. Xmos startkit & features a multitasking microcontroller. If you take a look at its code you'll understand how easy is to do : XMOS startkit basic Multitasking code

Hope this helps

mudz

Hi Remo, have a look here: http://www.doctormonk.com/2012/01/arduino-timer-library.html

This describes a timer library which allows the arduino to perform tasks at different time intervals, without "blocking" - ie waiting for one task to finish before it's possible to start another task.

I have used this library myself and found it extremely valuable.

Hope this helps

Neil

I would like to comment here, that the concept you have could work with some tweaks.

1. You only have a 10mSec timer using delay.

2. The while statement is what is stopping it from leaving and doing the other things.

You need to construct it using an if statement, and in my programming I often use a variable to know if I should do something or not. (I call it a flag but that's probably wrong)

I don't think you need extra libraries, but you've done the right thing and proved each piece of your code works, but combined they don't.

The Blinkwithoutdelay (stupid name) gives you the idea, but you are already using the millis() timer, and I find the example a little lacking as it's usually two tasks you want to do.

Without loading it, you might try something like ....

    if ((millis() - startTime_1 < valveOpenPeriod_1) && Valve1Open == 1)

    {

      myservo_1.write(180,30,false);   // tell servo to go to position 180 to open valve

      delay(10);                                    // waits 10ms for the servo to reach the position

    }

Obviously you'll need to set the Valve1Open = 1 or 0 as appropriate in your code.

Mark

edit ... minor typo.

Well, yes Neil...I think I will need to check this out...

But with all your help I actually have it working...at least I have 3 servos responding to 3 pushbuttons that start their valve open period.

And they do work simultaneously. Here it is...

// I am using this library...

#include <VarSpeedServo.h>

// I am creating 3 servo objects

VarSpeedServo myservo_1;

VarSpeedServo myservo_2

VarSpeedServo myservo_3;

// 3 digital pins

const int servoPin1 = 9;

const int servoPin2 = 10;

const int servoPin3 = 11;

// 3 valves can be set to 3 different open time

const long valveOpenPeriod_1 = 7000;      // 7 seconds

const long valveOpenPeriod_2 = 5000;      // 5 seconds

const long valveOpenPeriod_3 = 2000;      // 2 seconds

// store state of 3 servos, HIGH is open

int valveOpen_1;

int valveOpen_2;

int valveOpen_3;

// store last time servo was open

unsigned long startTime_1 = 0;

unsigned long startTime_2 = 0;

unsigned long startTime_3 = 0;

// attaches servos & pins to the servo object

void setup() {

  myservo_1.attach(servoPin1);

  myservo_2.attach(servoPin2);

  myservo_3.attach(servoPin3);

}

void loop()

{

  unsigned long currentMillis = millis();   // start counting

  if(digitalRead(2) == HIGH)                    // if inflation button #1 is pushed

  {   

    startTime_1 = currentMillis;                // reset start time to current time

  } 

  if(digitalRead(3) == HIGH)

  {   

    startTime_2 = currentMillis;

  }

  if(digitalRead(4) == HIGH)

  {   

    startTime_3 = currentMillis;

  }

// subtract startTime from current time and compare it to the valve period

  if(millis() - startTime_1 >= valveOpenPeriod_1)

  {

    myservo_1.write(180,30,false);        // valve opens until period is reached

  }

  else

  {

    myservo_1.write(90,30,false);           // valve closed when period reached

  }

// same for valve #2

  if(millis() - startTime_2 >= valveOpenPeriod_2)

  {

    myservo_2.write(180,30,false);      

  }

  else

  {

    myservo_2.write(90,30,false); 

  }

// same for valve #3

  if(millis() - startTime_3 >= valveOpenPeriod_3)

  {

    myservo_3.write(180,30,false);

  }

  else

  {

    myservo_3.write(90,30,false);

  }

}

In the code above, there is an issue that I can't explain.

Then I send the code to the Arduino, it thinks all the buttons have been pressed. In other words, all three valves open for the period they are supposed to be open, then they close.

This does not bother me except for the fact that I don't know why it does that.

Can anyone explain it to me?

// store state of 3 servos, HIGH is open

int valveOpen_1;

int valveOpen_2;

int valveOpen_3;

where is initial value = ???