How do i make a 555 timer circuit that turns on AFTER a time delay and stays on

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hi,
I dont go in for flaming, it serves no useful purpose.

IMHO, 'chemlec''s circuit is the the simplest circuit for this OP's application

The other second choice 'em2006' circuit is the one with the PNP transistor inverter on the output.

My circuit while functional, is only a poor third place.
 
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Aaaah, OK, see what you mean, thanks for not flaming

I guess that's one extra chip - 7408. However, I don't understand what you mean when you say 3 extra chips.

Also, the floating pin can be solved by connecting a resistor - however there is an immediate con to this: it would waste power. I did notice this and added an SPST switch to the circuit, but it would be an inconvenience. So, I can see exactly what you mean by this.

Thanks for clarifying all of this.


EDIT: Whilst I agree with the notation that chemlec's is the simplest, I don't understand how the circuit actually works. Would you mind clarifying this?
 
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JUST BUILD IT. IT WORKS GOOD and COSTS VERY LITTLE.
 

In 'chemlecs' circuit the timing resistor and capacitor have been switched over.

As suggested, just build it.
 
wow, until now i dodnt know there was a second or third page of discussion!
Whenever i visited the forum it didnt show up. it must have been some caching error or something, its happened before.

I will try to learn more about how all these gates and such you are talking about work, i havent really needed to know much of this until now, though, it shouldnt be too hard.
Anywa, thankyou for all your responses, youve helped a great deal!
 
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A 555 circuit is very wasteful when you are just powering a LED.
The same can be done with one or two transistors.
 
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A 555 circuit is very wasteful when you are just powering a LED.
The same can be done with one transistor.
 
How about showing your one transistor circuit to do the same thing so we have some common reference point?

And, I am still not clear on what you mean by "very wasteful." What is wasted in using the 555? Of course, seeing your one-transistor circuit may help answer that by allowing us to do a more compete cost analysis.

John
 
A 555 circuit is very wasteful when you are just powering a LED.
The same can be done with one transistor.
**broken link removed**

10 SECOND DELAY
This clever circuit turns on the LED 10 seconds after the power has been switched ON. The secret to its performance is the gain of the transistor.
With a gain of 200, the transistor will appear as a 470/200 = 2k3 resistor for the LED and for a 12v supply, this will create a current of 12-1.7 / 2300 = 4.4mA through the LED.
The 100u will take about 10 seconds to charge to a point where the base is 1.7v + 0.6v = 2.3v above the 0v rail. When the electro charges to this voltage, the LED starts to come on.
 
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A CD4541B oscillator/programmable timer costs $.48 at Digikey today. It needs one capacitor and two resistors for its oscillator. Its timer is programmed with jumper wires.
 
A CD4541B oscillator/programmable timer costs $.48 at Digikey today. It needs one capacitor and two resistors for its oscillator. Its timer is programmed with jumper wires.
Click to expand...

You can also use a PIC chip for 32 cents and it only needs one resistor.
 
At long last, saved! Thanks for the schematic, chemelec, and thanks for the link, Dr.james. I knew there had to be a way that a shadetree mechanic could work with.

Noticing in a sidebar that this thread is some two years old. Sure enough, Google never forgets.
 
The circuit shown by Chemelec in post #9 is the simplest to generate the desired delay and stay ON using a 555. Don't see the need for anything more complex.

To reset it you can connect a momentary reset switch between V+ and pin 2/6.
 
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