1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

Multiplexing project

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by mrn, Apr 6, 2013.

  1. mrn

    mrn New Member

    Joined:
    Apr 6, 2013
    Messages:
    81
    Likes:
    0
    Location:
    United States
    For some reason I though magnet wire was more expensive? the wire I bought was $9.00 vs $6.00 for a smaller gauge/thicker wire
     
  2. ChrisP58

    ChrisP58 Well-Known Member

    Joined:
    Apr 27, 2012
    Messages:
    1,081
    Likes:
    131
    Location:
    Provo, Utah, USA
    There is no reason that magnet wire should be more expensive. From a production point of view, it's about the simplest wire for electrical use to make. It's just a single strand of copper with a thin insulation layer.

    It may be more difficult to find at the hobby level though. Most magnet wire manufactured goes directly to the transformer, inductor, and motor winders. As such, the law of supply and demand for small users may run up the price.

    As for "people say 24 gauge wire will work." you have to look at all of the factors driving a choice. Most people choose a wire size solely for the current that will pass through it. In your case, you need to choose it base on resistance in order to control the current through the coil. The wire is not carrying current TO the load, it IS the load.

    You might try finding the right wire for your coil by a different route. Find a 5Volt, off the shelf miniature relay, and take it apart. First to see how much magnetic force it has, and second to see what wire size it is wound with. I'ts not likely to be a perfect match for your needs, but it'll give you a practical coil to use as a reference.
     
  3. mrn

    mrn New Member

    Joined:
    Apr 6, 2013
    Messages:
    81
    Likes:
    0
    Location:
    United States
    I tried a old power adapter, the wire was almost like thread, im not sure what gauge, however it would heat up super hot and very quickly just from the 5v 1amp adapter connected to it.
     
  4. dave

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    -
    Likes:
    0


     
  5. BeerBelly

    BeerBelly Member

    Joined:
    Sep 28, 2012
    Messages:
    262
    Likes:
    15
    Location:
    Northern California

    Use more windings on the coil and drop the voltage. You will get a lot better results.
     
  6. throbscottle

    throbscottle Well-Known Member

    Joined:
    Feb 1, 2012
    Messages:
    1,776
    Likes:
    113
    Location:
    Nuneaton, Warwickshire, UK
    You could also use a constant current supply, so long as the output voltage will go low enough.
     
  7. mrn

    mrn New Member

    Joined:
    Apr 6, 2013
    Messages:
    81
    Likes:
    0
    Location:
    United States
    @throbscottle: what do you mean by a constant current supply?
     
  8. BeerBelly

    BeerBelly Member

    Joined:
    Sep 28, 2012
    Messages:
    262
    Likes:
    15
    Location:
    Northern California
    Look up constant current source in Wikipedia. Then see the examples on Google images.
     
  9. ChrisP58

    ChrisP58 Well-Known Member

    Joined:
    Apr 27, 2012
    Messages:
    1,081
    Likes:
    131
    Location:
    Provo, Utah, USA
    @mrn, go back to post 78 where I mentioned current limited power supplies. While one may be useful in the discovery phase of finding the right coil characteristics, I don't think that it would be practical in your application, since they typically waste a lot of power in their current limit mode when feeding very low voltage loads.
     
  10. throbscottle

    throbscottle Well-Known Member

    Joined:
    Feb 1, 2012
    Messages:
    1,776
    Likes:
    113
    Location:
    Nuneaton, Warwickshire, UK
    I was thinking about your fluid control problem, and wondered if tiny solenoid valves are really the way to go. I learnt about inkjet and bubblejet print heads last week - maybe you could borrow an idea from there with piezo or thermal effects?
     
  11. mrn

    mrn New Member

    Joined:
    Apr 6, 2013
    Messages:
    81
    Likes:
    0
    Location:
    United States
    @Chris: ok I understand now.

    @throbscottle: Its actually not a solenoid valve persay, its just a electromagnet lifting a tiny little metal ball.

    I couldn't figure out what to use or how to make the fluid to heat up that quickly.
     
  12. mrn

    mrn New Member

    Joined:
    Apr 6, 2013
    Messages:
    81
    Likes:
    0
    Location:
    United States
    How would I go about setting up Ac current in order to demagnetize the electromagnets? would that mess up all the transistors and shift registers?
     
  13. BeerBelly

    BeerBelly Member

    Joined:
    Sep 28, 2012
    Messages:
    262
    Likes:
    15
    Location:
    Northern California
    Is this something that needs to be done between uses or something a field technician will do yearly during maintenance?
     
  14. mrn

    mrn New Member

    Joined:
    Apr 6, 2013
    Messages:
    81
    Likes:
    0
    Location:
    United States
    @BeerBelly: Its something that has to be done atleast twice a second, after everytime each coil is activated.

    Like when you apply power to a electromagnet then cut the power, the metal/iron core of the electromagnet still remains slightly magnetic, normaly the weight of what ever it is you are lifting would be enought to pull the object away from the magnet, however in this case the metal object being attracted to the magnet is so tiny it doesnt have enough weight to pull from the magnet when its shut off.
     
  15. BeerBelly

    BeerBelly Member

    Joined:
    Sep 28, 2012
    Messages:
    262
    Likes:
    15
    Location:
    Northern California
    A different magnetic material may be the answer. I'm not that knowledgeable on the subject but Permalloy instead of an iron electromagnet may cure this problem. Permalloy is many times better in attraction and losses it's magnetic field better when the electric current stops.

    Other options are more complex but are doable.
     
  16. mrn

    mrn New Member

    Joined:
    Apr 6, 2013
    Messages:
    81
    Likes:
    0
    Location:
    United States
    I did some reasarch its seams to be a very hard item to find as well as expensive.

    is there a way of cutting the magnetic field using ac current?
     
  17. MrAl

    MrAl Well-Known Member Most Helpful Member

    Joined:
    Sep 7, 2008
    Messages:
    11,026
    Likes:
    951
    Location:
    NJ
    Hi,

    You also have the items being picked up to worry about. Once they become slightly magnetized, they may attract to ANY metal not only the core metal.

    The way this is normally done is a decreasing AC current is used so that the metal goes though it's mag curve decreasing with each AC cycle. Alternately you could use another coil on the other side of the item being picked up, if that is possible. That would pull the item back down. You'd get as fast a response as you need im sure.\

    If you cant do that then perhaps a small magnet under each item to be picked up. As the item is picked up with the electromagnet coil on top, it has to fight gravity as well as the pull of the permanent magnet. Once the coil is de-energized, the permanent magnet does all the pulling and the item falls.
     
  18. mrn

    mrn New Member

    Joined:
    Apr 6, 2013
    Messages:
    81
    Likes:
    0
    Location:
    United States
    @MrAl: Right, however I wont have any other metal objects around, at least not that close.

    Another coil wouldn't work, however a magnet on the other side may work, however it would require allot more strength to pull the metal piece off the magnet.

    Would I be able to do a decreasing ac current in such rapid intervals? also would having ac current mess up the shift registers?


    maybe some sort of mechanical approach, like a sliding plate that just barely moves to knock the metal pieces off the coils, then moves back, it could be controlled by a dc motor or something. However this is kind of a lazy approach.
     
  19. throbscottle

    throbscottle Well-Known Member

    Joined:
    Feb 1, 2012
    Messages:
    1,776
    Likes:
    113
    Location:
    Nuneaton, Warwickshire, UK
    Just a thought here, instead of using a solenoid, why not build little linear induction motors? You can use approximately the same parts as a solenoid except the coil is driven by AC, so if you have a sufficiently high frequency the impedance comes into play so less current is needed. The moving part is made of a non-ferrous metal like aluminium so it's lighter, and de-gaussing is no longer an issue because there's nothing to retain the magnetism. You'd probably still need a ferrous core for the coil though - maybe a little ferrite bead of the sort you thread onto wires?

    You just have to be prepared to drive your coils with AC instead of DC. At a wild guess I'd try driving it in the low audio range.

    See illustration.
     

    Attached Files:

  20. mrn

    mrn New Member

    Joined:
    Apr 6, 2013
    Messages:
    81
    Likes:
    0
    Location:
    United States
    @throbscottle: that is a good idea, however would you have to have the retaining spring? could you let gravity drop it back down?


    also would ac current work with the shift registers?

    also would a induction coil using the same amount of materials be more powerfull then a magnetic coil?
     
    Last edited: May 25, 2013
  21. throbscottle

    throbscottle Well-Known Member

    Joined:
    Feb 1, 2012
    Messages:
    1,776
    Likes:
    113
    Location:
    Nuneaton, Warwickshire, UK
    The spring is just on the drawing as a means of holding the parts together, just do whatever you think - the return mechanism of the valve could do the same job. Without something to stop it though the disc could fly right off the coil.

    You would need some kind of driver since you would not be able to get AC out of any kind of normal logic chip,

    As to relative power, I have no idea, but I do know that induction motors are more efficient and powerful than the sort that has a commutator, but that doesn't mean the same rule will apply for such a simple arrangement as this, since I believe the efficiency gain in motors is due to the lack of switching.
     

Share This Page