LED to indicate off switch

Discussion in 'The Projects Forum' started by tee2, Nov 30, 2009.

  1. tee2

    Thread Starter Active Member

    Nov 19, 2004
    46
    3
    Hi,

    I have a project that I want to do this winter, but I'm ordering some part and would like to get whatever I would need for this too.

    I need to put a switch on my motorcycle to turn off the head light. When riding offroad at low RPM's the battery can run low to where the starter won't work. I would like to have an indicator LED that would be on when the headlight is off. Is there an easy way to do this. A bonus would be a bi-colored LED, red LED for off and green for on. The bike is 12V but I will have 5V from a USB outlet that is for the GPS.

    I did some searching on Google but am not to sure what to look for.

    Thanks
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Well, I just wrote a moderate-length reply that got thrown away - let's see if this will post.

    [eta]
    You'll need to find a suitable switch first.
    If you put the switch in the headlamp housing, you'll have two circuits to interrupt; one for high beam, one for low beam.

    If you put the switch between the high/low switch (on the handlebar) and the fusebox, you will have only one circuit to interrupt.

    Try to find a weatherproof switch rated for 10A. A boating supply place would be a good bet.

    Adding an LED to indicate the lights were turned off will be pretty easy - just an LED and a resistor across the switch contacts. If the switch is open, the LED will light up. There won't be enough current to turn on the headlamp, just the LED.

    The intensity of the LED will be the problem; it might be hard to see in daylight, but it will be very bright at night - you probably want that anyway for the "Headlamp Off" indication.

    You should look for an LED that you can mount in a watertight enclosure (or that comes in one), and preferably is wide angle. Narrowly focused LEDs will be somewhat hard to see unless you are looking right at them, and then they will be too bright.
     
    Last edited: Nov 30, 2009
  3. tee2

    Thread Starter Active Member

    Nov 19, 2004
    46
    3
    Thanks for the reply,

    I be cutting the power to both hi and low so one switch.

    I checked some boating stores, and the switches are north of $15. I'm going to get some cheaper ones under $2 (I need some mini and regular toggles) and get a waterproof boot for the top and epoxy the underside. I can replace it if it goes bad.

    I am making a dashboard that will mount under the windscreen by the headlight, to mount the switches, outlets (5V USB w/switch, 12V Powerlet w/switch), 2 LED's for the blinkers L and R. My full face helmet blocks my view of the the stock turn signal. I would like to have some type of volt meter, but I only have about 1" X 2" to work with ( for the meter) , so I am open to suggestions for that.

    I am really looking to have the LED "on" when the head light it off. Is there a way to do that? A friend has a switch and what happens is after riding off road and having the light off, he would get on the road and forget to turn the light on, and twice he got pulled over for no headlight. I want something that will scream I'M ON.

    For the blinkers I have been trying some 3mm supper bright and they work good. I will use some panel mounts to hold them in with some epoxy on the back. I seen some flat top LED that are wide angle on EBay and was going to get some of them.

    Thanks
    Todd
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    This should work for you:

    [​IMG]

    I've calculated R1 based on an LED rated for 2v @ 25mA, with a system voltage of 14v.

    If you want to use a different LED, re-calculate R1 as:
    R1 >= (14v - Vf_LED) / DesiredCurrent
    Use a resistor that is greater than or equal to the result.

    Keep in mind that a $15 switch is a bargain compared to a $100 ticket. Buy for reliability, not purchase price. This is a safety item.

    I'm surprised you don't have a highbeam/lowbeam indicator already.
     
    Last edited: Nov 30, 2009
  5. tee2

    Thread Starter Active Member

    Nov 19, 2004
    46
    3
    Thanks, I'll breadboard it tonight.

    I sounds to simple. I see that when S2 is open current flows through R1 and D1 and it lights. The thing that is confusing me is, why when S2 is closed (power to L1 or L2) would D1 be off? It seems that D1 would always be on.

    I do have a Highbeam/lowbeam indicator. I don't use the high beam much it just lights up too wide and not far ahead. I would like to convert to a HID but that is too $$$$$ for now.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    Would you like for it to be more complicated? :D

    By the way, you can use that same resistor & LED combination to test for blown fuses.
    When S2 closes, it basically short circuits the current path across R1/D1, so there is no voltage across the LED. It won't light up with no voltage going through it.

    Ahh, OK. Yep, HID's can get expensive.

    Oh, DON'T use "electrical tape" or "electrician's tape" on the wiring! It will get gummy and fall off within a year, and you will have problems.

    Good soldering and heat-shrink tubing is the way to go. Properly applied heat shrink tubing won't come off, until you cut it off.
     
  7. tee2

    Thread Starter Active Member

    Nov 19, 2004
    46
    3
    Thanks Sarge, I made a mock-up today and it worked like you said. Thanks.

    Once I get this done I'm going to tackle a LED brake light that will flash a few times than stay on. I have found the plans from a search here, it uses a 4093 IC. I should be able to build this with few problems. I may have some questions about LEDs and a way to switch them (transistors, relay). I'll ask when I'm ready.

    Todd
     
  8. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Good deal. :)

    Sure. Start a new thread/topic though - that way they won't get confused.

    When you do start the new thread, post a link to the existing thread that you found; that will make things go a good bit faster.

    [eta]
    In view of the safety aspects of the taillight project, you must not make any changes to the existing lighting. However, you might add DOT approved marker lamps, say to the back of saddlebags.

    4000 series CMOS probably shouldn't be used in automotive-type systems. You really need to use circuits that are specifically rated for automotive environments, and take special precautions to ensure they will be safe if anything breaks.
     
    Last edited: Mar 16, 2010
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