Controlling HMI's Knob position 360 degree in both direction using arduino

Hello all,I am working on a project which deals with controlling the HMI's Knob(which in turn has pot behind) using Arduino. I wants to select a cycle (or functionality of appliance in general) by turning the knob to a specific angle (360/n degree for n cycles).I have following queries

  1. what is the standard and easy approach to do this
  2. i thought of using motors then question is
    should i use stepper motor+encoder(to get the feedback) OR servo motor(which can run 360 or so) which has encoder with in as i am confused after reading so many answers here
    3)In both above cases which one is more accurate and precise in terms of position control ?

please help !!

Hi,
Welcome to the forum.

Please read the post at the start of any forum , entitled "How to use this Forum".
OR
http://forum.arduino.cc/index.php/topic,148850.0.html.

Can you tell us your electronics, programming, arduino, hardware experience?

Tom..... :slight_smile:

HI,
I am an post-graduate engineer in embedded system.Have used several microcontroller as LPC2148,cortex-M and little bit of arduino ,RPi.
But i have not played with these servo and steppers before.Since 3-4 days i am playing around with Microservo(RC).What i am bale to do with that micro servo is following

  1. Easily can send command to move 0-180 degree(using writeMicroseconds(us) which is 500-2500 us in my case to move 0-180 degree)
  2. I removed the mechanical hindrance and now the servo can move around 360 degree ( i have not removed the Potentiometer feedback yet)
  3. i have taken a wire soldered to potentiometer output and using analogRead() to read the voltage which is coming around 68-591(mapped output to 0-1024) for 0-180 degree correspondingly.
    Now i turned the potentio-meter manually and read the voltage.I can see output is increasing and thus conclusion i made is servo-controller is not allowing input greater than range(500-2500us) and thus i can not get angle more than 180 degree.
    I am thinking of breaking the feedback going from potentiometer to servo controller and then fix that reference voltage and control externally to stop at particular angle.Is this right??
    And also i am in doubt that i will lack the accuracy! please help

Can you replace the existing pot ?

If YES, there are motorised pots are available with a simple DC motor and gearing integrated.
You’d use an h-bridge to drive that motor with your code.
If NO, then some form of mechanical coupling to the pot shaft is needed.
You’ll also need some reduction gearing or coupling like that used in an RC servo - to get the low speed and torque needed. A stand-alone motor position is arbitrary, and will need some feedback to your program, so you know where it is.

A servo MOTOR is fine (basically the same as a DC motor) with internal feedback & gearing, but as you noted, most RC SERVOs are limited in their rotation to around 180 degrees. They’re convenient because they are ABSOLUTE positioners... you just tell it to go to X, and if it can, it will.

Stepper motors are also fine - different approach, which you control via driver from your code. Steppers are also positioned RELATIVE to a known point... often a limit switch, or encoder feedback.

Thanks for the reply!
In case I can't replace the existing pot, and I need to rotate the existing pot by servo motor(around 360 degrees both ways) then is there any servo that I can buy which can provide needed rotation as well POSITIONAL feedback and I can control the angle ?? (please prove the link if there any)
Or DC stepper motor is the only way to go ??
IN case I can replace the existing pot then, please provide the link for those motors which I can control
Which one is an easier approach ??

This may help, but you could do it yourself...
https://www.google.com/search?q=motorised+pots&rlz=1C9BKJA_enAU768AU768&hl=en-GB&biw=768&bih=911&tbm=isch&prmd=sivn&sxsrf=ALeKk03JSKiv3s7LmI06zuqNnRhF8U3Dwg:1583331378284&source=lnms&sa=X&ved=0ahUKEwi08_KCgYHoAhXOe30KHXPWBh0Q_AUIEigC

Good 360 RC servos are relatively expensive, and the cheap ones lose the feedback, so they won’t help much.
Steppers - you need to address the mechanical linkage issue, and the position calibration / limit.

Depending on what you’re actually trying to do, my choice would probably be one of the pots in the link...

Hi,
What is the application, what is the pot controlling, what device?

Thanks.. Tom.... :slight_smile:

around 360 degrees both ways)

720 degrees travel, or 360 bidirectional ?

Words mean a lot if they’re used properly.

"In case I can't replace the existing pot, and I need to rotate the existing pot by servo motor(around 360 degrees both ways) then is there any servo that I can buy which can provide needed rotation as well POSITIONAL feedback and I can control the angle ?? (please prove the link if there any)"

RC sail winch servos probably make ~6 rotations, so they may rotate too much for the accuracy you may need. Reading the OP posts, there seems to be a pot that is turned by the "HMI" (?) knob. Can the wiper of this pot be tapped for reading it's position indicating voltage output? The pot in the modified servo, does it output a changing voltage range thru the full 360 rotation of the servo horn?

Thanks lastchancename for clear answer !
I am trying to automate the knob control using arduino instead of turning knob manually in order to select a cycle of an appliance.One of my HMI's example is below in picture link

Motorised pots will need h-bridge to drive and i read that they can just give you the direction and speed control but not the position control.and thus to control position i need to create controller much like in servo ! Also h-bridge is costly ??
I came across the motor named Parallax Feedback 360° High-Speed Servo which seems to give me desired functionality.

is it better option ?

Can't see much in the image you linked..

s-l300.jpg

I havent used the Parallax or any other 360 feeddback servo, but it looks like it might do what you need...
and here's the servo you didn't link to...
https://www.robotshop.com/en/parallax-feedback-360-high-speed-servo.html?gclid=Cj0KCQiAwP3yBRCkARIsAABGiPrd6_gGRvxqWJfxJ-bBni5hR3bX2qtWt-_bCY4G6VeSl_foaW5geqEaAo4LEALw_wcB

I'm sure you can do these things

s-l300.jpg

Hi,
What does the "pot" do?
Does it have clicking positions, or is it a smooth rotation.

WHAT IS THE DEVICE/MACHINE, WHAT VARIABLE DOES THE CONTROL ADJUST?

Tom.... :slight_smile:
(Its LBFAS). :o

zoomkat:
. Can the wiper of this pot be tapped for reading it's position indicating voltage output? The pot in the modified servo,

yes i can tape it !

zoomkat:
does it output a changing voltage range thru the full 360 rotation of the servo horn?

No only till 180 degree and that's the reason i am planning to go for parallex 360 degree servo which gives feedback for 360 degree and more

TomGeorge:
Hi,
What does the "pot" do?

What is pot supposed to do ! varying the voltage

TomGeorge:
Does it have clicking positions, or is it a smooth rotation.

it is smooth transition between steps.So it has some steps kind of rotation for every cycle there is a step

WHAT IS THE DEVICE/MACHINE, WHAT VARIABLE DOES THE CONTROL ADJUST? [/quote]
It is HMI of a washing machine which internally adjusts the voltage i hope

Tom.... :slight_smile:
(Its LBFAS). :o

“yes i can tape it !”

Then you feedback position for the HMI knob. Would take some doing, but you might use this, thru an arduino A0 pin, to drive a continuous rotation servo that would turn the knob. What s the voltage being supplied to the internal pot connected to the HMI knob?

Actually my project has to be general in the sense that it is not the voltage always which will be varying behind the HMI pot.So my only task is to turn the knob without looking behind the knob's encoder variable.
So till now i am only having one option in my hand that is parallax feedback 360 servo motors to track the position