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Blog Christmas Spirit-tron updated schematic (Christmas Spirit Meter)
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  • Author Author: garengllc
  • Date Created: 29 Dec 2019 7:18 PM Date Created
  • Views 1337 views
  • Likes 3 likes
  • Comments 4 comments
  • holidayspecial19ch
  • holidayspecial19ch.
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Christmas Spirit-tron updated schematic (Christmas Spirit Meter)

garengllc
garengllc
29 Dec 2019

OK, here is an updated schematic; it is actually the exact same as before minus a pull-up resistor on the FETs.  So how about I explain things a little more and maybe we can see what I messed up this time image.

 

So the FETs are P-Channel setup up as a low-side load.  I like to use low-side because then I don't have power always on at the other end of the Drain.  In this application, there is no power in the system at all unless it is being cranked, but it is just a habit, so I did it here.  The LM3914 has open-collector outputs on the Lx pins.  Because of this, the pins float when not "enabled" and are current sinks when they are.  That is a 10k pull-up between the Gain and the Source on the FETs.  When the Lx pin is not "enabled," the pin will float, which means it will be weak-pulled high to the voltage on the Source pin (15_V_2 in this case).  When "enabled," The Gate will be pulled low, passing the 15_V_2 from the Source to the Drain; when this happens the bulbs will essentially be connected from 15V to ground, lighting them up.

 

image

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Top Comments

  • jw0752
    jw0752 over 5 years ago +2
    Hi Jason, Thanks for the explanation. I mised seeing that the FETs were P Ch on the first schematic. This circuit is actually more elegant than the one I proposed as it doesn't need the inverters. I look…
  • garengllc
    garengllc over 5 years ago in reply to jw0752 +2
    Thanks, this turned out MUCH less complicated than I usually make things! I had posted some videos in a comment to one of my posts, so I gave them their own blog post to make them easier to find. https…
  • shabaz
    shabaz over 5 years ago +1
    Hi Jason, I just saw the video, Christmas Spirit Meter Great project : ) I'd like to make this for next Xmas : )
  • garengllc
    garengllc over 5 years ago in reply to shabaz

    Awesome, I am glad to hear it!  Reach out if you have any questions.  Good luck!

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  • shabaz
    shabaz over 5 years ago

    Hi Jason,

     

    I just saw the video, Christmas Spirit Meter

    Great project : ) I'd like to make this for next Xmas : )

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  • garengllc
    garengllc over 5 years ago in reply to jw0752

    Thanks, this turned out MUCH less complicated than I usually make things!

     

    I had posted some videos in a comment to one of my posts, so I gave them their own blog post to make them easier to find.

    https://www.element14.com/community/blog/update-post.jspa?ID=34272&draftID=494596

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  • jw0752
    jw0752 over 5 years ago

    Hi Jason,

    Thanks for the explanation. I mised seeing that the FETs were P Ch on the first schematic. This circuit is actually more elegant than the one I proposed as it doesn't need the inverters. I look forward to seeing your project in action.

     

    John

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