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Help please!

Discussion in 'General Electronics Discussion' started by neilsy, Nov 16, 2013.

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  1. neilsy


    Nov 16, 2013
    I'm a bit of a beginner but essentially wanting to build a circuit that operates as follows, but have no idea how to do it!

    Basically I have a wind up torch and am wanting to connect to a chain of LEDs. I would like it to operate so that the faster you wind the torch, the more LEDs in the chain will light up, i.e. the LEDs will essentially be acting like a crude measure of how much energy your producing. So turn it slowly the first might light, turn a bit faster the first and second LED light etc.

    Any help would be really appreciated!
    Thanks :)
  2. duke37


    Jan 9, 2011
    Will the LM3914 bargraph display chip do what you want?
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    As I understand, most of these devices charge a battery as you wind (it seems intuitive to use a super cap, but I think rechargeable batteries are cheaper.

    As such, your effort in winding will correlate pretty closely with the charge current.

    So an intuitive response is to insert a sense resistor, amplify this voltage, and then use it to drive something like an LM3914.

    However, the power available from your rechargeable battery is likely to be insufficient do drive such a circuit, and an external battery would be a nonsensical addition.

    I'm not sure what a good solution might be. Perhaps you could use such a circuit with a boost SMPS regulator, but you might end up sapping your batteries a significant portion of your charging effort just to tell people how hard they're working.

    I'm not sure it's in the beginner range, simply due to the power requirements of the simple solution vs. the power availability.

    What other electronic circuits have you built?

    Have you ever built any electronic circuit of your own design?
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