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

Thread Starter

Rolland B. Heiss

Joined Feb 4, 2015
236
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!
 

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Thread Starter

Rolland B. Heiss

Joined Feb 4, 2015
236
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.
Thanks for the time you took trying to help when you could have been doing something else. Very much appreciated wayneh.
 

KJ6EAD

Joined Apr 30, 2011
1,581
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.
 

cmartinez

Joined Jan 17, 2007
7,418
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... ;)
 

WBahn

Joined Mar 31, 2012
26,398
I bet this is what you have on the left side.

An
Astable Multivibrator !
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.
 

Thread Starter

Rolland B. Heiss

Joined Feb 4, 2015
236
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! :)
 
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