555 circuit double-check

Thread Starter

Georacer

Joined Nov 25, 2009
5,182
I found this circuit posted by Bill_Marsden in a thread over at Homework Help section, thread name "pleaseee helppppppp" (very imaginative title).


I tried to build it just for fun but it seems to give a constant low on the output, lighting only the red switch, no matter how desperately I push the pushbutton. Could someone try to test this circuit, just to find out if it's me or the design that's problematic.

P.S. I ran the circuit on 5V Vcc and used the NE555N

Thanks for your time.
 
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Wendy

Joined Mar 24, 2008
23,415
I'm in the process of running experiments on it (as I just finished the ebook article today).

One thing you can try is connect pin 2 to Vcc, the output will be low and stay there. Then connect pin 2 to ground, the output will go high and stay there.

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OK, just breadboarded it using this layout...



It works over the entire power supply range, 4.5V to 15V. The red wire is a 2" (500cm) wire folded in half. It substitutes for a push button.

I had a moment I doubted it though, it appears one of the kids spilled something (milk for cereal?) on the bread board. I had to work the connections to get them to make reliably.
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Thread Starter

Georacer

Joined Nov 25, 2009
5,182
Yes, it works now. I guess I 'll never find out what i did wrong. I have a question though. When I push the button very fast, the LED's don't flip. Could it be that the capacitor doesn't have time to charge? That means that there's a maximum frequency of operation. I also can't understand why this ciruit doesn't work without the capacitor? Shouldn't the Vout from pin 3 reach pin 2 through the resistance? I also noticed that if we override the resistance between pin 3 and the switch we experience a lot of bounce wich I guess is the reason you inserted the RC circuit.
 
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Wendy

Joined Mar 24, 2008
23,415
On the submission. I seem to work differently than the other guys, I prefer to write in public, sometimes we have a had a few go off and start ranting (hello, did I leave the bathroom door open... again?) but mostly it is positive.

If I mis-spoke myself or got something flat wrong it allows it to be corrected before it winds up in the book. I'm also always looking for new and interesting ideas, thought the circuit does not have to be original.
 
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