555 question

Is it possible to use 555 to generate a pulse which triggers after
every 24 hours. Am I looking at an RC time constant which is not at all
feasible ?

 

With a supercap, you could think of getting a few hours
with 20% accuracy. Your 24 hours is out of reach, as
Mr. Fields states. You need to be thinking about some
kind of digital accumulation of a shorter interval that can
be done more accurately.

 

I would try a 4060 or 74HC060(CMOS).
It contains a oscillator and a counter.
H.T.H

 

No, and even if you could how long would it take to calibrate. A week, 2
weeks ....

Cheers.

 

No, that's why Exar introduced the 2240, which was a 555 (though without
some of the pins externally available) in a package with a 7-bit binary
counter. Via feedback you can set the divider to whatever you want,
and then you run the 555 at a decent rate. As people have pointed out,
you can then adjust the clock almost immediately, and you don't fuss
with the impossible of getting suitable components for such low timing
rates.

I have no idea if the 2240 is still available.

Of course, you might look at what the end game is. Having a detector
to note when the sun comes up (or goes down) may provide the same
effect, given that you specify 24 hours.

Michael

 

I was trying the same thing, and was able to accomplish this with a huge
electrolytic, and a huge value capacitor that would cycle every 12 hours,
quite accurately.
I once saw a circuit that pulsed a 555 every couple of hours, advancing a
4017. Once the 4017 advanced the required number of cycles, it reset, and
began counting again. so if you could get a 555 pulsing every 2 1/2 hours,
with a 4017 having 10 outputs , your pretty close.

 

Michael Black wrote...

Exar's XR-2240 was second-sourced, often with the same part number.
Plus there was Fairchild and TI's uA2240, and NSC's LM2240. In
the old days you could find one of these at suppliers like Jameco.
I looked and didn't see any, so perhaps it's the end of that era.

In the back of my mind I think there's a similar chip... Aha, yes
now I remember, it's Intersil's icm7240 series, also made by Maxim.
These are still available. For example, the popular ICM7242 is an
8-pin chip with a 555-style oscillator driving an 8-bit divider,
see http://www.intersil.com/cda/deviceinfo/0,1477,ICM7242,0.html

To finish the story, there are some other single-ICs using the
'2240 '7240 oscillator-plus-counter idea, but without the classic
relatively-precise 555-style oscillator. Examples are the CD4060
or 74HC6060, the mc14536 or mc4541, plus Philips' 74HCT5555, etc.
These use a different type of simple CMOS relaxation oscillator.

Unless you succumb to the PIC crowd :>), you may want to explore
a two-chip solution, which allows higher oscillator frequencies.

 

Not by itself. There's no way to generate a RC constant with any accuracy
over that long a period of time.

Right.

It's tasks like this where flash microcontrollers really excell. Something
like a small PIC or AVR can knock out this application with a single chip
and no external parts except for maybe a transistor switch to get to the
same 200 mA output current of the 555.

BAJ

 

It might be easier to think backwards, use a presetable DOWN counter and
look for the borrow or terminal count pin to go active. This eliminates the
extra gates.

 

i guess if you pass it through a few flip flips, and use an And/Nand
gate combined with the input train and output train to reset the
flops after an event, that way you could set the duration with in a
spec that is suitable for the timer and simply scale it longer via
flip-flops

 

I have another idea. Why not use a sound sensor triggered by an alarm
clock. So the output of the sound sensor can trigger 555 monostable
multivibrator.

 

If you make the 555 pulse once for every 1.5 minutes, a single 10 bit
counter would cover more than 24 hours.

 

And $150.00 worth of development system, and however long it takes to
learn to program it.

Here's the _real_ answer:

http://www.ee.washington.edu/stores/DataSheets/cd4000/cd4060.pdf

Good Luck!
Rich

 

Perhaps yes! Otherwise this is best way I ever came across.

 

Only if you want to spend it. Homebrew programmers like my Trivial Programmers
can be breadboarded in less than an hour's time and for less than $15 in
Radio Shack parts.

My Trivial programmers are located here:

http://www.finitesite.com/d3jsys

You can program in assembly, no doubt. All of the development and programming
software is free.

While I recommend that if you're going to be doing this long term that you
be familiar with assembly, for a quick head start writing in a high level
microcontroller language like JAL may be the ticket. You can find JAL at
http://jal.sf.net. Also Wouter van Ooijen has a JAL based simple blinky LED
application for many type of PIC microcontrollers here:

http://www.voti.nl/blink/index_1.html

It's an answer for this application.

However any investment of time or money in a microcontroller can be amortized
over a bunch of projects. And even if it's truly a one off (which I doubt
once the utility is realized) $20 and an afternoon learning the basics of
how to program the part isn't that big an investment. The next project
won't have a 4060 or the 555 as a solution. However it's likely that a
bootloaded 16F88 for example can do this project, and the next one, and the
one after that.

BAJ

 

Well there can be many more tricks, all depends upon how easily you
want the things to be done!

 

There's a much simpler way if you want to go that route.

Buy a cheap battery driven clock with hands. Something like the module
outlined here:

http://www.du.edu/~jcalvert/tech/quartz.htm

Now remove the minute and second hand leaving only the hour hand.

Set up to pass the hour hand through a slotted sensor like this one:

http://www.embedded.com/showArticle.jhtml?articleID=10700612

Now with a simple 1.5V battery and a clock module you get a signal exactly once
every 24 hours. Use something like a 555 to guarantee a single trigger
and that's about it.

BAJ