555 question

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.

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--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

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Not by itself.

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

"aman" wrote in news: snipped-for-privacy@g14g2000cwa.googlegroups.com:

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

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.

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 Thanks,
    - Win

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

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

Cheers.

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

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 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

message

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at all

And/Nand

and

eliminates the

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.

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:

Good Luck! Rich

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

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

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:

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

Also Wouter van Ooijen has a JAL based simple blinky LED application for many type of PIC microcontrollers here:

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

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:

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:

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