Re: coutdown 555 timer values?

John Fields wrote: 
On 22 Jul 2005 14:01:01 -0700, "aman" <aman.bindra@xxxxxxxxx> wrote:


You might want to consider a simple 8 bit microcontroller like PIC. All
micro-controllers have timer interrupts. If not using a CD4017 as a
counter and using 555 to generate a 30 sec pulse seems like a good idea.



---
It may seem like it is, but in reality it isn't.

He would have to add some logic, like some SR flip flops and a bit more. I just get worried about the stability of more than a minute versions of 555s.

Note that the OP wanted six timeout periods all starting at once, but
as they timed out, each one lasting 30 seconds longer than the one
which timed out before it.  Like this:

      ___
T1___|   |__________________________________________

      ______
T2___|      |_______________________________________

      _________
T3___|         |____________________________________

      ____________
T4___|            |_________________________________

      _______________
T5___|               |______________________________

      __________________
T6___|                  |___________________________


You can't do that with a 4017.

I'll bet you could come up with something neat based on the 4015 shift register.
.

Relevant Pages

  • Re: coutdown 555 timer values?
    ... John Fields wrote: ... >>You might want to consider a simple 8 bit microcontroller like PIC. ... >>micro-controllers have timer interrupts. ...
    (sci.electronics.basics)
  • Re: coutdown 555 timer values?
    ... >You might want to consider a simple 8 bit microcontroller like PIC. ... >micro-controllers have timer interrupts. ... Professional Circuit Designer ...
    (sci.electronics.basics)
  • Re: How to design this circuit?
    ... Don Lancaster wrote: ... >> John Fields ... no way to know when the next pulse is going to happen. ... That means the longest delay will be at the longest time between any ...
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  • Re: Delay without affecting pulse width
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  • Re: Adding delay to the pulse
    ... John Fields wrote: ... a duration by about the 'on' time of the first pulse. ... A one second delay is a bit long for a bipolar 555 - one ot the CMOS ...
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