Connect with us

My first circuit

Discussion in 'General Electronics Discussion' started by completenovice, Jun 23, 2013.

Scroll to continue with content
  1. completenovice

    completenovice

    8
    0
    Jun 23, 2013
    Hi
    I'm brand new to electronics and no idea what I'm doing
    I'm thinking of making this circuit. The power supply is a USB cable, about 5V and about 500mA. Each diode (they're LEDs by the way) are 20mA and 3-3.5 V each. Will this circuit work or do I need any sort of resistors or anything? Also if I add in a variable resistor will that allow me to change the brightness of the LEDs?
    Any help appreciated
    Thans
    Sam
     

    Attached Files:

  2. davenn

    davenn Moderator

    13,833
    1,950
    Sep 5, 2009
    hi there

    welcome to the forums :)

    just take the top row of 4 LED's for a start
    you said they are 3 - 3.5V each.
    Work out the total voltage and then tell me why that wont work off 5 V ;)

    Dave
     
  3. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    Last edited by a moderator: Jun 23, 2013
  4. completenovice

    completenovice

    8
    0
    Jun 23, 2013
    I'd forgotten about the anode and catode on the diagram, I know the way the negatives and positives that should go in relation to eachother. Assuming all those are correct is would it work?
    Thanks
    Sam
     
  5. davenn

    davenn Moderator

    13,833
    1,950
    Sep 5, 2009
    hi Sam

    Yup OK so as Bob said, your sets of LED's are reversed .... just change the polarity of the battery to solve that

    BUT still ... no it wont, read my post above again.
    you have 4 x 3V what does that equal?
    you said your supply voltage is 5V

    do you see the problem ?

    Dave
     
  6. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    Sorry dave, but you Ninja'd me. I was composing mine when you posted.

    Bob
     
  7. davenn

    davenn Moderator

    13,833
    1,950
    Sep 5, 2009
    no probs :)
    just a hint tho, don't always give the full answer straight away let them work it out
    it just helps them to learn a little more ... rather than being spoon fed :)

    see with his response he hadn't read what I said about the voltages .... lets see if he figures out his problem ;)

    Dave
     
  8. completenovice

    completenovice

    8
    0
    Jun 23, 2013
    Ok, so I have 10 LEDs in total running at roughly 3V. Does that mean I need a thirty volt supply or what?
    Sorry I'm a compete novice
    Thanks for bearing with me
    Sam
     
  9. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    No, it means you cannot put them in series. They have to be in parallel and have a reistors in series with each one.

    Did you bother reading the tutorial I pointed you to?

    Bob
     
  10. completenovice

    completenovice

    8
    0
    Jun 23, 2013
    Yes I did, I just became lost after a few lines. My only electronics experience is a short Unit on it in GCSE physics which isn't much use, I read the parts of the tutorial which were about what I needed and didn't understand, hence I came back here.
    Thanks though :)
    And thanks for that advice too, I understand what I need to do now and how it will work :).
    Sorry for my cluelessness (if that's a word)
    Thanks alot again
    Sam
     
  11. completenovice

    completenovice

    8
    0
    Jun 23, 2013
    after listening to what you've both said, had another look at that tutorial and after finding a couple of equations online. I have come up with this, does it look anybetter and does the resistance of my resistors look realistic ie will they work do you think?
    Sorry for going on about this
    Thanks a lot
    Sam
     

    Attached Files:

  12. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    Much better! That will work, assuming your power supply can supply 200mA.

    Bob
     
  13. duke37

    duke37

    5,364
    771
    Jan 9, 2011
    To get positive at the top,which is the norm, the battery has to be inverted.

    The leds will then conduct. The arrows should point down to conduct in pnp or npn transistors or leds.
     
  14. completenovice

    completenovice

    8
    0
    Jun 23, 2013
    Thank you both for bearing with me
    You've helped me a lot
    I couldn't complete my project without your help
    Thanks
    Sam
     
  15. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    I can't believe I missed that the polarity was still wrong.

    Bob
     
  16. completenovice

    completenovice

    8
    0
    Jun 23, 2013
    what it's wrong? I though the whole thing just needed flipping / inverting
    Sam
     
  17. completenovice

    completenovice

    8
    0
    Jun 23, 2013
    Oh yes I've seen it now. It's just that the LEDs should be the other way right? + to + and - to -. I've got them the oppisite way
    Is that the problem
    Thanks
    Sam
     
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

-