Connect with us

Potentiometer

Discussion in 'General Electronics Discussion' started by Rockgirl, Aug 27, 2021.

Scroll to continue with content
  1. Rockgirl

    Rockgirl

    8
    0
    Aug 26, 2021
    Hi, I need help. Can I find any potentiometers where the rotation angle is smaller than usual? Usually it's I guess 290 degrees but can somewhere find about 90 degrees? I need a 100k potentiometer that adjusts the 90 degree rotation, I don't know if they are anywhere.
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    11,702
    2,717
    Nov 17, 2011
    Can you use a 330 kΩ potentiometer and limit the rotation mechanically to 90 °?
    I'm not aware of 90 ° potentiometers off the shelf.
     
  3. Rockgirl

    Rockgirl

    8
    0
    Aug 26, 2021
    Oh I'm not sure. Maybe I need to open up more about what this is all about. I bought a bidirectional DC-motor controller. I would like to use a potentiometer on the joystick. But the joystick can't turn it enough. If there was any trick to make this work?
    Maybe this brings even more difficulty, but I would supply this controller with either 12vdc or 24vdc. Does it make this more difficult?

    I tried to put a picture of the connection but it doesn't work :(

    I hope you could help me with this problem.
     
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    11,702
    2,717
    Nov 17, 2011
    Resize to < 300 kB.

    Which model? Can you provide a link to the technical data / datasheet of the controller?
     
  5. Rockgirl

    Rockgirl

    8
    0
    Aug 26, 2021
    Last edited by a moderator: Aug 28, 2021
  6. bertus

    bertus Moderator

    2,056
    776
    Nov 8, 2019
    Hello,

    Why do you need a 90 degrees potmeter?
    The circuit uses a standard 100 k potmeter:
    bi_speed_contol.png
    Bertus
     
  7. Rockgirl

    Rockgirl

    8
    0
    Aug 26, 2021
    I already mentioned it above in the post. Because I want use joystick and the trajectory of the joystick is not enough.
     
  8. bertus

    bertus Moderator

    2,056
    776
    Nov 8, 2019
    Hello,

    You can adjust the range for the circuit with the 100k and 10k resistors on adjusting stack.
    You could make the circuit and measure the voltage on pin 3 of IC1a.
    Then you can calculate the needed resistors in stead of the 100k and 10k.

    Bertus
     
  9. Rockgirl

    Rockgirl

    8
    0
    Aug 26, 2021
    Oh I guess I don't know how to do that :(
     
  10. Harald Kapp

    Harald Kapp Moderator Moderator

    11,702
    2,717
    Nov 17, 2011
    You're not alone in searching a pot with 90 ° rotation angle. All references I can find mention standard 270 ° pots with mechanically limited rotation angle. The ones that have "90 °" in the title of the sales offer refer to the angle between the pins and the potentiometer axle as 90 °, not the rotation angle.

    In your circuit the pot is used as a voltage divider together with the 10 kΩ resistor at the lower end and the 100 kΩ resistor at the upper end. It thus delivers these voltages to pin 3 of IC1a:
    0.05 × V+ when in the lower position,
    0.52 × V+ when in the upper position
    You cannot achieve this exact ratio by simple means. You can approximate it, however:
    • Remove the upper 100 kΩ resistor by a short circuit.
    • Change the lower 10 kΩ resistor to 5 kΩ (use 2 × 10 kΩ in parallel or use 4.7 kΩ, good enough)
    • Change the gain of IC1a from 1×to 2× by adding two resistors in the feedback as shown e.g. here. The value of the 2 additional resistors is not important. both shall have the same vale in the range 1 kΩ to 10 kΩ, whatever you have in your parts bin.
    • Mechanically limit the potentiometer to move from the left side (lower pin in the diagram) to left side + 90 °.
    Using 4.7 k will give you these divider ratios:
    0.1 × V+ in the lower position
    0.72 × V+ in the upper position.
    You can tweak (fine tune) these values by changing the gain f the opamp IC1a from 2 to another (lower) value. Do this by changing the resistor values in the feedback circuit according to the equations given in the link I providd above.
     
  11. VenomBallistics

    VenomBallistics

    285
    57
    Aug 30, 2018
  12. Rockgirl

    Rockgirl

    8
    0
    Aug 26, 2021
    Hi, I would like to try this. Would it be possible for you to show (draw) how this is done for example in this picture you added?
    I’m a girl and this isn’t my strongest skill, not yet at least :) I'm afraid if I destroy this controller by doing wrong :( I want to be sure what I do. I know how to solder and I know some basic stuff about electronics but I’m not sure about this.
     

    Attached Files:

  13. Harald Kapp

    Harald Kapp Moderator Moderator

    11,702
    2,717
    Nov 17, 2011
    Here you go:
    upload_2021-8-28_14-43-13.png
     
  14. Rockgirl

    Rockgirl

    8
    0
    Aug 26, 2021
    Okay, I'll try this tomorrow. I still have to ask if I understood correctly, so can I add those new two resistors to something between 1k -10k? Thanks :)
     
  15. Rockgirl

    Rockgirl

    8
    0
    Aug 26, 2021
    The solution was found closer than I could imagine. I found an old joystick potentiometer. It looks bigger compared to other potentiometer. I check those multimeter and I get 110k ohms. This potentiometer work those angle which I want. But why do these pots work differently? Are joystick pots some way different?

    Another issue related to this bi-directional control. Is it a feature of this control that it does not start running the engine completely at zero? When I rotate the potentimeter the motor starts to buzz at the beginning and then it suddenly starts to rotate. I don’t mean it starts rotating at full, but about 3-4 volts. Why doesn't the motor run in the 1-3v range?
    No matter which potentiometer is used for this, the potentiometer will not affect this. I would like this to work in the same way when I give power to the motor power supply unit, when I start from zero and add volts the motor starts a little quietly spinning up to 1 volts.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-