Please help me identify what this circuit board is designed to do

Discussion in 'General Electronics Chat' started by Rolland B. Heiss, Feb 4, 2015.

  1. Rolland B. Heiss

    Thread Starter Member

    Feb 4, 2015
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    Picture 6.jpg Today at a thrift store I picked up an old Sears Tach/Dwell/Voltmeter with other misc. things. One of them was this circuit board and I don't know what it does apart from the fact that it seems to partly consist of some sort of joule thief circuit. I plugged in a 'dead' 9v battery to it and the green and red LEDs flash on and off in approx. 1 second intervals and have been doing so consistently for over an hour now. Any help or explanation would be most appreciated! By the way, I'm new to this community so hello everyone!
     
  2. wayneh

    Expert

    Sep 9, 2010
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    A good picture of the reverse side would help. Is that an empty IC socket?
     
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  3. Rolland B. Heiss

    Thread Starter Member

    Feb 4, 2015
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    It's been nearly two and a half hours now and the LEDs are still blinking strong and consistently on the 'dead' 9v.
     
  4. Rolland B. Heiss

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    Feb 4, 2015
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    Thanks for your response wayneh! Here's am image of the flip side. By the way, it looks like an empty IC as nothing seems to be connected to it.
     
  5. wayneh

    Expert

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    Can you get anything better? It looks like there is no connection between most of the components.
     
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  6. Rolland B. Heiss

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    Feb 4, 2015
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    I know, that's what confounds me!
     
  7. wayneh

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    It could just be for fun and looks, or maybe a practice board. Use more light and see if you can get a better shot. Maybe someone here will recognize it.
     
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  8. wayneh

    Expert

    Sep 9, 2010
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    Do the LEDs alternate? My kids made a board in school called "Blinky" that would alternate two LEDs.
     
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  9. Rolland B. Heiss

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    Feb 4, 2015
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    Thanks for the time you took trying to help when you could have been doing something else. Very much appreciated wayneh.
     
  10. Rolland B. Heiss

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    Feb 4, 2015
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    Yes, the LEDs alternate.
     
  11. darrough

    Member

    Jan 18, 2015
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    What I notice is that there is no output or input. In other words, no speaker, no buttons, no header pins, no sensors, et cetera.
     
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  12. KJ6EAD

    Senior Member

    Apr 30, 2011
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    The seven "channels" on the right suggest the possibility of something to do with a seven-segment display but it's probably just an introductory soldering practice board with a two-transistor astable multivibrator driving the LEDs as a kind of instant gratification feature.
     
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  13. Rolland B. Heiss

    Thread Starter Member

    Feb 4, 2015
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    Here's a video of the board and what it does:

     
  14. KLillie

    Member

    May 31, 2014
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    I bet this is what you have on the left side.
    [​IMG]
    An
    Astable Multivibrator !
     
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  15. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    It could also be a one side two-layer board (though I doubt it very much) You could check that with your voltmeter, checking for continuity between different components. Or, more likely, it's only a soldering and part placing practice board for students that's already been assembled.
    Nice guitar... BTW... ;)
     
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  16. WBahn

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    Mar 31, 2012
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    It's close, but not quite. There are only three resistors and the Vcc supply goes through a single resistor that then goes to the emitters of both transistors (per the silkscreen label on the front, anyway, assuming I'm making out the letters correctly, which is debatable).

    Would be nice to have a cleaner shot of both sides.
     
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  17. Rolland B. Heiss

    Thread Starter Member

    Feb 4, 2015
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    I appreciate everyones input and thank you all for your respective contributions. It's quite an interesting little board and it's still blinking steadily after nearly 24 hours. The usual setup for a board of this apparent type as spoken of by KLillie with the shared schematic uses 4 resistors but this one only has the three which WBahn was quick to point out. Yet the result seems to be the same. At the moment I'm not sure why but I'm fairly new to electronics and I really like this site! By the way, thanks for the comment related to my guitar cmartinez! :)
     
  18. MikeA

    Member

    Jan 20, 2013
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    Glue it to your chest and go through an airport security checkpoint. TSA will identify it for you. :D
     
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  19. Rolland B. Heiss

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    Feb 4, 2015
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    LOL!!!! Good one MikeA!
     
  20. wayneh

    Expert

    Sep 9, 2010
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    That's the Blinky circuit widely used for kids' projects. The 3 resistor version makes good sense but I think that 4 are often used to make it a little easier for the kids to understand?
     
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