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How To Detect When A Line Goes Low

Discussion in 'General Electronics Discussion' started by benlyboy, Mar 10, 2017.

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  1. benlyboy

    benlyboy

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    Mar 10, 2017
    Hi new to this forum so let me know is this is miss using it, but I could use some help.

    I am basically new to electronic circuit design, played with it when I was a kid but haven’t for years.

    i am restoring a vintage motorcycle and as the turn signal bulbs are no longer available I decided To convert them to LEDS.
    I don’t want to modify the bikes wiring at all. So I made my own led bulbs to fit the bike. I have built a circuit using a good old 555 timer to flash the LEDS that works great too, except that it runs all the time even when the turn signal isn’t on.
    The bike is a very simple circuit. battery to flasher then the turn signal switch onto bulb then ground.
    The flasher is a two pin flasher one in, one out ( I added a ground to power the circuit)
    what I want is to some how monitor the out put line from the flasher relay and detect when it is an open circuit and when it is grounded, and switch the flasher accordingly.

    How would i do this...?

    Thanks for any help or ideas
     
  2. shrtrnd

    shrtrnd

    3,763
    485
    Jan 15, 2010
    Just a thought. Have you tried the J.C. Whitney website to see if they have direct LED replacements for you
    old bulbs?
    Can you post a diagram of what you built?
     
    CDRIVE likes this.
  3. AnalogKid

    AnalogKid

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    Jun 10, 2015
    It sounds like the flasher is a series bi-metal switch, and your LEDs do not draw enough current to make it cycle. You can test this with a resistor in parallel with one of your LED bulbs. Something sized to pull 1 A should make the original flasher flash. If that works, it tells us more about how the bike works and what to do next.

    What is the bike voltage and the original bulb part number?

    ak
     
  4. benlyboy

    benlyboy

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    Mar 10, 2017
    I will try and draw up the circuit diagram of my circuit, though it is just a basic 555 timer circuit with a 5v voltage regulator feeding it power, i added the voltage reg because I found the flash rate changed when the bike was running ether because of the increased voltage, or maybe because of ripples in the DC from the generator.

    The system is 6v, and yes you are right it had a bi metal type flasher in series. I cant test the resister thing as I don’t have a working flasher. the bike was a basket case when I got it,,, and was missing the flasher how ever I know that what you suggested would work,

    I know there are easer ways to do this. I could probably find something on line that would work, or buy a replacement stock flasher and us resisters. But I thought it would be fun and I might learn something trying to build one :)
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    One of the problems with a 555 oscillator is that the first period is longer because the capacitor has to charge from 0V to 2/3 Vcc rather than from 1/3Vcc to 2/3Vcc. In practice I'm not sure now significant that is.

    Mechanically, you need to be careful that vibration doesn't cause components to snap off. A good fix for this is potting the circuit, however if you do this, remember it makes the circuit hard to repair later on down the track.

    LEDs are very sensitive to changes in voltage. For this reason, it can be problematic to power several in series from a voltage source which varies. In your case, assuming you're using white LEDs and simply a resistor to set the current, I'd advise not placing two in series, and having one resistor per LED.
     
  6. benlyboy

    benlyboy

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    Mar 10, 2017
    Thanks Steve, you bring up all good points, I had notice a slight delay in the start of the 555, however its not really that much of an issue. but it is nice to know way it does that so thanks.

    Your point about vibration is also a good one. though in my case as the bike is a vintage bike and will not see a great deal of road time I’m thinking it will most likely be ok.

    On your third point, by dumb luck that how i wired my LED so clever me:)

    I’m guessing what I’m asking here must be harder than I thought, as no one has suggested anything.

    I guess it would be easy if the line I was trying to check was ether high or low, but with the flasher even with the switch on there can be two states high and low. So i need to somehow not check its state so much as I need to see if its an open circuit. Not sure how to do that.
     
  7. AnalogKid

    AnalogKid

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    Jun 10, 2015
    It isn't harder than you thought, we're just coming up to speed. Just to be clear, you are after a total replacement for the original series flasher - yes?

    If so, then the circuit has to be such that the turn signal switch both enables the flasher and directs its output to the correct bulb. One approach is to let the 555 run continuously, and if the first blink is a bit short, so what. This sounds like what you said in post #1, but you didn't say why you don't like it.

    Does not modifying the bike wiring include not cutting wires. Two 555 circuits, each powered by one output from the turn signal switch, will do what you want.

    ak
     
  8. benlyboy

    benlyboy

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    Mar 10, 2017
    Thanks for the reply.

    Yes I’m looking for a total replacement for the stock flasher. I do not want to modifying the bikes wiring in any way for a number of reasons. just one being if the bulbs ever become available I would like to be able to return it to stock. The bike is also over fifty years old and its just not good to start cutting on wiring that can not easily be replaced.

    OK now the part that will make some of you think I’m nuts :)
    I am using the run all the time system now and you are right it works just fin, except it didn’t sound right, yip you read it right:)

    Also the light are a bit dimmer than I want because of the voltage regulator, easy to fix run the light off the full voltage of the bike not directly off the 555 timer that is running on five volts

    I could use a transistor to do this but I want the click of a relay, nuts!!! I know but it just sounds right, but not if it is running all the time.
     
  9. AnalogKid

    AnalogKid

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    Jun 10, 2015
    I'm not an expert on bike electrical systems, but based on my auto designs I don't think you need a voltage regulator for the 555. Power transient protection should be good enough in a 6 V world.

    The relay part makes this thread make sense. And I agree that there is no substitute for getting the aesthetics right. Without messing with the native wiring, can you get a ground wire to where the new flasher circuit will be installed?

    ak
     
  10. benlyboy

    benlyboy

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    Mar 10, 2017

    Hi thanks for the help
    Yes adding an extra ground is as easy as grounding the flasher pack to the frame. As for the voltage regulator, not sure why it worked, but if did fix the problem I was having where the lights would flash much faster when the engine was running.
     
  11. AnalogKid

    AnalogKid

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    Jun 10, 2015
    You should post your circuit. A 555 is designed specifically to reject supply voltage variations.

    ak
     
  12. benlyboy

    benlyboy

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    Mar 10, 2017
    a very quick drawing of the circuit I have so far... didn’t ad values for caps and resistors, i would have to look now to know. the reg is a LT805CV

    flasher-a.jpg


    [Mod edit: image resized]
     
    Last edited by a moderator: Apr 9, 2017
  13. benlyboy

    benlyboy

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    Mar 10, 2017
    i had no replies but I’ve been working on it on my own, i may have come up with something that with some work may work.

    In the circuit below trans 1 would work only if the relay was open and the switch was shut. Trans 2 would only work when the relay is closed so in theory if the switch is closed one of the trans would be open depending on the relay state. if you open the switch and the relay is open the system shuts down. if the relay is closed it would remain running till the relay opened.
    Any one have any ideas, this id far from a complete circuit so help would be great :)

    test2.jpg



    [Mod edit: image resized]
     
    Last edited by a moderator: Apr 9, 2017
  14. benlyboy

    benlyboy

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    Mar 10, 2017
    Thought I would let you know i came up with something that seems to work, at lest on a breadboard.
    below is the circuit i came up with.

    flashert.jpg



    [Mod edit: image resized]
     
    Last edited by a moderator: Apr 9, 2017
  15. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    There are a couple of problems.
    1. You need a reverse biased diode across the relay coil to protect the 555 from a high voltage spike as the relay is turned off.
    2. The protection circuit can probably be a 10 ohm resistor followed by a 9V zener diode and a 100uF capacitor. A voltage regulator is not going to work correctly for a number of reasons not worth explaining (unless you're interested)
    3. 6V is fairly low for a 555.
    4. You probably want to use a 5V relay. The alternative is to use a transistor or mosfet to switch a larger relay.
    upload_2017-4-9_20-32-40.png

    I've only shown the power connections and the output here.
     
  16. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    That circuit has the potential to short out your battery, or at the very least flatten your battery.
     
  17. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    That seems quite complex.

    I'd need more information about how the indicator switches work to be able to suggest something better though.
     
  18. benlyboy

    benlyboy

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    0
    Mar 10, 2017
    Thanks for the reply. as i said im very new to this so the advise is gratefully accepted.

    Steve it a very simple system on the bike. its a two pin flasher so in and out, It is however easy enough to pick up a ground to give power to run the circuit. I don’t want to modify the bike wiring any more that that though.

    Thanks again for the help

    flasherw.jpg
     
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