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 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
4040 troubles
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Feifer



Joined: May 16, 2012
Posts: 46
Location: San Diego

PostPosted: Sun Nov 10, 2013 3:28 pm    Post subject: 4040 troubles Reply with quote  Mark this post and the followings unread

Hi all,
I'm having problems with this chip and was hoping someone out there could help me out. For some reason timing diagrams are hard to come by in data sheets for this chip. The only one I could find was for the MC14040, which jameco says is the same thing. http://www.jameco.com/Jameco/Products/ProdDS/12950MOT.pdf

The way I have it set up is since it triggers on a falling edge, I have my clock pulses going through an inverter. So when the clock is off, the input is held high. I have a push button going from V+ to reset and when I push it, all Qs go low, as they should. The problem is when I release it, Q1 goes high, which, according to the timing diagram it shouldn't do until the input goes low. Is the CD4040 set up slightly different? Any way I could get around this?
Thanks
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Feifer



Joined: May 16, 2012
Posts: 46
Location: San Diego

PostPosted: Sun Nov 10, 2013 5:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

Okay. For a stupid little chip with only 2 inputs, this gremlin is being really hard to track down. I put it back on the bread board and it works just fine. I put it in the socket on the pcb (exact same circuit) and it does it's weird game. Ready to throw this thing at the wall.
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elmegil



Joined: Mar 20, 2012
Posts: 1503
Location: Chicago
Audio files: 14

PostPosted: Mon Nov 11, 2013 7:58 am    Post subject: Reply with quote  Mark this post and the followings unread

Does your clocking source have some bounce in it? Breadboards have lots of extra capacitance, perhaps that's filtering out some stray glitches that your PCB is seeing?

I'd try putting a cap on the input, something like the RC Debouncer shown in this doc:

http://www.eng.utah.edu/~cs5780/debouncing.pdf
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Feifer



Joined: May 16, 2012
Posts: 46
Location: San Diego

PostPosted: Mon Nov 11, 2013 1:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

Well I found the culprit. I had a capacitor on the reset input tied to V+ meant to initialize the chip upon power up. Not entirely necessary but a nice little feature. Why it was working on the breadboard but not on the pcb I have no idea.
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