yet another 555 question.

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dacflyer
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yet another 555 question.

Post by dacflyer » Sat Sep 28, 2002 8:07 pm

:( a diagram whould be most appreciated...thanx

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Chris Smith
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Re: yet another 555 question.

Post by Chris Smith » Sat Sep 28, 2002 9:59 pm

If you keep all circuits powered, and don't disconnect batteries etc, it should start out in one state only, always. Are you running extreme values for the caps or resistors, and also if the first state is incorrect, use a invertor to make it flip. The "Iffy" circuit you describe sounds like you have floating leads, or extreme values in your components? That or too much/little voltage or a spiked 555, once damaged but still working. Too much load will do that, over heating? Change your 555 to check?<p>After re-reading, you cant start a 555 via a power up, and expect it to choose a state. They make great random number generators [0-1s] doing this. Im sure you could lessen the chances, but its not the way to go. Disconnect any other way than this method. Use a push on to start your 555, already powered up. They only draw tiny amounts of power so it would last on batteries for months.<p>[ September 28, 2002: Message edited by: Chris Smith ]</p>

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Re: yet another 555 question.

Post by bridgen » Sun Sep 29, 2002 5:45 am

You can ensure that the output starts low at switch-on by having a small C from the RESET pin to ground and an R from the RESET pin to Vcc.
You can then have the output stay low until you want it to go high by having a C from the TRIGGER pin to Vcc and an R from the TRIGGER pin to ground.
The CR on the RESET needs to be fairly short and that on the TRIGGER needs to be 3 secs.
You can play around with Cs and Rs like this to do all sorts of things.
e.g. for the solution to another 555 problem see the first part of the ELECTRONICS page on my web site www.davidbridgen.com.

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dacflyer
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Re: yet another 555 question.

Post by dacflyer » Thu Oct 03, 2002 1:44 pm

ok, i tried as you suggested,,
didn;t work,,, perhaps i need to change other connections?

heres how i have all connected


pin 1 = gnd.
330k = pin 1 & pin 2
10uf = pin2 & pin8
pin 3 output
100k = pin4 & pin8
0.47uf = pin4 & gnd.
pin 5 = blank
pin 6&7 tied
pin8 B+ = 12v

i hope you understand this... i made connections as you suggested,, the timer seems to start hi for micro second then just off ( lo )
i am sure i have missed something somewhere here...i opted to try this on a 555 1st to make sure it works before i , use a 556..less complicated...
please let me know if you need more info.. thanks..

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Chris Smith
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Re: yet another 555 question.

Post by Chris Smith » Thu Oct 03, 2002 2:08 pm

If you have an email address, I have many diagrams for the 555 and 556.<p>I cant find one so far, that even comes close to you configuration? <p>Most have 4 and 8 tied together & positive, Cap on 1&2, not resistors, etc?<p>[ October 03, 2002: Message edited by: Chris Smith ]</p>

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Re: yet another 555 question.

Post by russlk » Thu Oct 03, 2002 3:38 pm

The 555 is designed to start high and go low after the time delay. You have to use it that way and invert the output, connecting it up backward is not going to invert it's operation.

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Re: yet another 555 question.

Post by viveguy » Fri Oct 04, 2002 3:56 pm

Go to epanorama.net or web ee.They have lots of links to ideas,circuit configurations,and 555 calculators.
I do find it odd that you are having a hard time finding the circuit you want.The 555 was the most experimented with IC on the planet until stamp computers came along.
Try expanging your web searches.You may be surprised what you will find.

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Re: yet another 555 question.

Post by dacflyer » Sat Oct 05, 2002 9:49 am

i was going by what dave said in the post before my last one.<p>[email protected]

bridgen
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Re: yet another 555 question.

Post by bridgen » Thu Oct 10, 2002 12:29 am

I was wondering how your project is coming along ? I presume you have the (delay) 555 working as you want now (with nothing connected to pins 6 and 7, as I said in my email).
Regards, David

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Re: yet another 555 question.

Post by dacflyer » Mon Oct 14, 2002 10:27 am

david, see above...i tried as you said,, did not seem to work,,, i also been very sick the last 2 weeks, so i haven't done much either... look at my connections above and tell me if i need to make changes,, thanx...

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Re: yet another 555 question.

Post by bridgen » Mon Oct 14, 2002 11:07 pm

Sorry you've been ill, hope you are okay now.
Your connections as per you posting are correct except that pins 6 and 7 should not have anything connected to them nor should they be connected together.

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Re: yet another 555 question.

Post by dacflyer » Wed Oct 16, 2002 4:56 pm

ok, i will try this again soon...i'll let you know

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Re: yet another 555 question.

Post by dacflyer » Sat Nov 09, 2002 11:02 am

david !...hey i finnaly got it to work thanks a lot,, you was a big help....i still need to filter the B+ tho,, auto noise makes it false trigger sometimes..but its a minor problem,,,thanx again

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Re: yet another 555 question.

Post by bridgen » Sat Nov 09, 2002 7:03 pm

Good ! But I'm glad I didn't hold my breath !
Ive modified my web site (www.davidbridgen.com) a bit and will start keeping circuits and/or solutions posted there if I think they may be of interest to other people.
Regards.

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