SMD LED circuit with motor
  • Hi folks. I was working on a scale modeling project for installing LED lights as navigation lights on a plastic model kit with a little micro cell phone motor to spin the prop. All this is to be mounted on a little wooden base with a little slide switch. The SMD LED's are from eBay (pre-wired).

    So if you can picture the circuit:

    I have the (2 x AA) 3v battery holder in the middle with a separate slide switch which I will mount on the underside of the model base. On the right I have the 3V micro motor, a 3V white, 1.9V green and 1.9V red LED's all in parallel. The Green and Red LED's have 51ohm resistors upstream.

    On the left side in series I have a flashing red 3V LED, a 1.9V red LED with a 51Ohm resistor upstream and three more 3V White LED's.

    Note both circuits are connected to the same battery sitting in the middle (pictorially). All LED's are SMD's, with the Flashing Red as the regular LED with legs/ prongs.

    Questions are:

    1) Will this work?
    2) Do I need more power? Not that I intend to run this all day. It's more so just for display? On for maybe a minute or two and then Off.
    3) The Flashing Red normal LED in the series circuit is supposed to make the other SMD LED's in the series circuit also flash. Is this arrangement ok? or should I just buy another flashing LED and make a separate parallel independent circuit for the 1.9V red LED in the series circuit? The idea is to make the red SMD LED flash. Can't install the normal flashing LED on the model as it's too big. It will just be tucked away underneath the model base.
    4) I Had to work with SMD LED's as the regular ones are way too too big to install anywhere on my model as navigation and/ or taxiing lights.

    Any help will be appreciated. many thanks.
  • 1) Mostly no.
    2) Mostly no. But if you add up all the voltages in your series circuit, you'll see that it can't run on 3 V.
    3) A flashing LED in series with regular LEDs will also cause them to flash. However, if you're going to run all those things in series, you'll need a higher voltage power supply. But then you'll also need to decide how you're powering your parallel circuit and your motor circuit.
    4) Whether you use SMD or thru-hole LEDs doesn't make much difference, so long as you know their specifications. 

    Here's an article that may help choose a resistor for your circuit, as well as think about what kind of power supply you might want for various circuits:

    Here's an article that gives an example circuit of using a flashing (or in our case, flickering) LED to drive regular LEDs:
  • Thanks a lot Lenore.........back to the beginning for me.

    Let me read those articles of yours. Maybe you can show me how to calculate the total voltage required for this circuit, and/ or perhaps suggest a better design?

    I am having trouble here attaching a simple Jpeg picture. The error message states that it is a huge number of characters too long, simple copy/ paste not working. The file size is only 79 Kb?

    cheers. .