All pins reserved by servo. I cant use a DC motor at the same time.

Hi everyone, I have just started to use MATLAB with arduino for a university project.

I'm trying to use both a servo and a DC motor with an arduino, but when I initialise the servo motor, all the pins (or at least the PWM ones) become reserved to the servo.

a = arduino('COM4', 'Uno', 'Libraries', 'Servo')
s = servo(a, 'D11', 'MinPulseDuration', 0.00055, 'MaxPulseDuration', 0.0024)
writePWMDutyCycle(a, "D9", 1)

The error I get is:

"Digital pin D9 is reserved by Servo in 'Reserved' mode. To change the pin configuration, clear all variables holding onto this resource."

I have tried other pins, but they are all reserved. If i don't initialise the servo, it works.

How can I reserve just one pin for the servo and not all of them?

Thanks

Answer 1

[Madhu Govindarajan]

Can you try configurepin command to set it as Digital Output or Digital Input depending on your application?

Or does that also error out?

[Massimiliano Zingarelli]

I have tried configurePin(a,'D9','Unset') and other things isntead of "unset" but it gives me exactly the same error I got earlier

[Randy Hodges]

I am having the exact same issue. I currently cannot get the writePWMDutyCycle function to work when I have servos attached to my arduino. Using configurepin gives the same error

[Brian O'Connell]

Why is this an accepted answer when it doesn't answer the question?

I have students with this same question. It's not a consistent issue, only showing up for some students. I have not noticed a trend in operating system or version yet. Has there been any work to solve or address this issue?

[Eric Davishahl]

Bumping Brian's question. I also have a few students (not all) experienceing this issue and the configurePin approach does not resolve it.

Answer 2

[Madhu Govindarajan]

I only have an MKR1000 at my disposal right now and here is what I tried with no error messages. See if a similar approach works for you on Uno.

a = arduino 
configurePin(a,'D9','Servo')
configurePin(a,'D10','DigitalOutput')
s = servo(a, 'D9', 'MinPulseDuration', 0.00055, 'MaxPulseDuration', 0.0024)
writePWMDutyCycle(a, 'D10', 1)

This did not give me any errors, but I do not have actual devices connected. So I cannot confirm that the hardware is doing what it is supposed to. But there are no reasons why it should not.

HTH

[Levi Montgomery]

Doesn't work either. I still get the error any time I want to write to a digital pin (not the one I am using for my servo) . Marked your suggestion with %%%%%%%%%%

clear
a = arduino();

% below is adapted from MiniProjectCollectData by Neil Moore
writeDigitalPin(a, 'D9', 1); % on
pause(0.1);
red = readVoltage(a, 'A0');
pause(0.1);
writeDigitalPin(a, 'D9', 0); % off
%
s1 = servo(a, 'D6', 'MinPulseDuration', 700*10^-6, 'MaxPulseDuration', 2300*10^-6);
while 0==0
    if red < 0.0195506
        material = "mousepad";
        writePosition(s1, 1)
    else
        if red < 0.058651
            material = "calculator";
            writePosition(s1,.75)
        else
            material = "folder";
            writePosition(s1, .5)
        end
    end
    fprintf("Your material is %s!\n ", material)%%%%%%%%%%%%%%%%%
    configurePin(a,'D9','DigitalOutput')        %%%%%%%%%%%%%%%%%
    writeDigitalPin(a, 'D9', 1); % on
    pause(0.1);
    red = readVoltage(a, 'A0');
    pause(0.1);
    writeDigitalPin(a, 'D9', 0); % off
    
end

Answer 3

[Daniel]

This issue is caused by the way the Arduino Servo library handles pins. Their documentation states that "use of the library disables analogWrite() (PWM) functionality on pins 9 and 10, whether or not there is a Servo on those pins."

https://www.arduino.cc/reference/en/libraries/servo/

So, the fix for this issue is to not use the pins that the Servo Library disables while using the Servo Library, which worked in this similar situation:

https://www.mathworks.com/matlabcentral/answers/1698815-all-pins-reserved-by-arduino-servo