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sunrise 12th March 2009 07:25 PM

NE555 two times delay
2 Attachment(s)
i have found out this schematic - it is one delay time to power the relay on after some time - but also has a flashing LED that stops flashing after the relay is turned on...

what i want to make is a TWO TIME DELAY (after one time runs out, first relay powers on and than after second time runs out, the second relay powers on) and the LED that will flash until the second time has run out and after that time it stays solid...

i have some trouble with understanding logic circuits. To old i guess.


sunrise 12th March 2009 07:45 PM

i know that i could have almost the same thing by paralleling two of these circuits ... but i would like one LED and two times and two relays.

please help,

Steerpike 12th March 2009 11:07 PM

You can add a "c" timer, but you need the C timer to be the shorter time period timer.
Switch on system... after a short delay, timer C times out and switches its relay, but A is still 'counting', so the led still flashes.
Timer C will by electrically not connected to A or B, merely sharing the same power supply.

Construct timer C the same as timer A, but link the output pin of the 555 (pin 3 ) to the 'C' relay only - and not to any other 555. And compute the timing the same way as for timer A, but use a bigger capacitor, or smaller charging resistor.

Do you have the relevant formulae for 555 timing components?

sunrise 13th March 2009 05:56 AM

steerpike - thank you for the interest in this thread. thank you very much.

yes - i need three NE555. A, B and C. From the schematic in the first post of this thread, A timer needs to have also his own relay, and the C timer needs to have his own also. So in fact i have two timers that will have theirs separate relays an one timer that will flash the LED until the timer A runs his time out. So, what you propose is to simply construct a timer C the same way as timer A (but with shorter time), and also to simply connect it to pin 3 of the timer A. Right?
The problem is, which pin of the timer C i should connect to the timer A - pin 4 or ????
That is what i am not sure about - I know that relay A is a timer and that i need 2 of them but how to connect them with the timer B to have everyhing running like i want it......:bawling:
that is what i do not know. :( Formulas are also not a problem.
Thanks for any replies,

Steerpike 13th March 2009 03:40 PM

2 Attachment(s)
The picture should show it all. Timer C operates totally independantly of the other 2.

This MAY not suit your application - i don't know what it is - since a fault in the 'C' timer, would not stop timer A from switching. A will switch after its time period, whether C is working right or not.

If that is going to be risky, and if you need that A is allowed to switch ONLY if C has switched, and if C never switches, then A must be stopped from switching, that requres a little more complex wiring, but is still doable.

It is usual to put a 0.01uf capacitor from pin-5 to ground on the 555 chip, to make it less susceptible to noise.

sunrise 13th March 2009 07:50 PM

i need just that - that A is allowed to switch ONLY if C has switched, and if C never switches, then A must be stopped from switching. That is exactly that i had in my mind.

Steerpike 13th March 2009 09:16 PM

2 Attachment(s)
I think this will do what you want then:
"A" will not start its timing cycle until C1's negative end is grounded. C1's negative end is only grounded after Timer "C" has switched its relay on.

sunrise 13th March 2009 09:42 PM

Mr. Steerpike - I thank You so much... this brought the smile on my face. Thank You again.

sunrise 14th March 2009 02:07 PM

Mr.Steerpike - i have a question...
i have read somewhere that NE555 might turn on even if capacitor is not present - when resistor is going to the pin2 of the timer? i will post a schematic, in this post, where the capactior is added to prevent turning on...
The question is - timer A - could it turn on even if capacitor is not connected to ground (because of resistor going from psu to pin2)??

sunrise 14th March 2009 03:35 PM

2 Attachment(s)
i was thinking maybe something like this would also work? (just to avoid the capacitor being connected to ground by the first timer- how about that)

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