# 32h timer (555??)

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#### pixi

##### New Member
is it posible to build a timer of a ic 555 that vill give a signal every 32 houers??
my english are not so god, sorry

#### laroche73

##### New Member
32 hr timer

Yes, but first you need to find a really big capacitor...

Seriously, pixi, a 555 is not the best way to generate long time delays, and by long I mean anything over 10's of seconds. Accuracy suffers, because the tolerances on timing resistors and capacitors are poor at the values needed to generate long delays.

There was another request along similar lines under the Datasheet/Parts request forum

which didn't generate much of a response because it was posted in the wrong forum. I meant to post a few schematics there using some CD4000 series ICs, but haven't gotten around to drawing them up yet.

There are lots of ways to make an accurate 32 hour timer, the most important question being, what kind of ICs do you have access to, aside from the 555?

Like many of the posts I've come accross in these forums, my first recommendation would be to employ a cheap microcontroller like the PIC12F629 (~ $1 U.S.). They have a nice low-power mode that uses a standard 32Khz watch xtal. A cheap programmer can be made using your PC's parallel port and a buffer chip like the 74HC125. If you don't have access to micros, can you get CMOS 4000 series parts? The ones that would be useful here (in decreasing order of importance) are the 4536, 4060, 4020, and 4040. The ranking is based on the number of divider stages each chip has, as well as whether the IC includes an on-chip oscillator (The 4045 is meant to be a free-running timer, and doesn't have a reset pin, so it's not as useful here). - CAL #### nettron1000 ##### New Member A 555 timer is perhaps ok for rough timing intervals where accuracy is not of great importance. But if you want real accuracy a crystal driven frequency divider is the way to go, as Laroche already pointed out. There was a thread running awhile back which mentioned using a HEF4059 IC, a programmable divide by n counter which as a max division of 15999, which was driven by a crystal oscillator. I'll post a link to the thread just as soon as i can find it again, but heres a link to the data sheet for the 4059. https://www.electro-tech-online.com/custompdfs/2003/09/HEF4059B_CNV_3.pdf #### laroche73 ##### New Member CD4000 series Nettron, I agree that the 4059 was a nice part in it's day. I follow a few simple rules when using CD4000 parts. 1) Don't use anything you can't find in the Digi-key catalog (this rule applies to an amazing variety of other parts as well). Digi-key provides a good barometer of market prices. If you're planning to use a part frequently, buy in quantities of 25 to get the price break. OK, I see the 4059A there. On to #2. 2) Don't use anything that was only made in the "A" series (unless you have a specific need for the unusual properties of "A" series devices, like the unbuffered inverters, for example). Also check to see if the part was popular enough to make it to the "HC" or even better, the "VHC" series. Wait a minute. Phillips made the RCA4059A in a "B" version? is it still available? 3) Check the cost. Digi-Key currently sells the CD4059A for$5.15 (qty 1) in a 24-pin DIP. They also sell the far more useful flash-based (re-programmable) PIC12F629 in an 8-pin DIP for $1.63, ($1.03 for qty 25).
Two 4059s would be needed to get to the 32 hr mark, vs. a single F629.

(it's an unfair comparison, but should provide pause for anyone considering obsolete parts - unless it's all you have available.)

There may be better rules of thumb to follow, the point when asking questions is to check out what's available in your area, and include the information in postings. - CAL

ps. the 4059 is a 14-stage binary counter, you can get the same thing for less cost in a 4020 or a 4060 (osc included). The divide-by-N feature can be useful for some apps but really isn't needed for making a 1 or 32 hr timer. 2^n powers are sufficient if you start out with a 32Khz clock source.

#### nettron1000

##### New Member
Two 4059s would be needed to get to the 32 hr mark, vs. a single F629.

(it's an unfair comparison, but should provide pause for anyone considering obsolete parts - unless it's all you have available.)

Laroche, i think you missunderstood what i meant ( mostly my fault), i meant to use the crystal driven frequency divider as an highly accurate time base, not to generate the 32 hour time interval.

The rule of thomb for time base accuracy is; the higher the frequency you are dividing down the better accuracy you will get.

I agree that a microcontroller would be suppior to using cascades of counters, thats assumming the original poster is comfortable with programming and doesnt mind the extra "baggage" that comes along with it , e.g. software compiler , associated cables and connectors ( I think that would have to be considered in the cost as well).

Im no authority on processors, but i read somewhere that they dont keep accurate time. So i was wondering how accurate a software generated timing scheme would be ? I also read that there are MC's that have prescalers built-in, im not sure what purpose thats serves, but wouldnt they make for a better timer ?

P.S. When looking for parts i always browse around surplus outlets to get the better deals rather than limit myself to component whole salers or retailers.

#### laroche73

##### New Member
timers and micros

Hey Nettron, hope my post didn't sound too snippy, you brought up a reasonable objection to using micros. There is a substantial amount of baggage associated with micro design, but it's quite possible to set yourself up on the cheap. Most come with free assemblers, and there are some fine freeware "C" compilers available (SDCC and GNUAVR are two that come to mind). And it may be a dirty word these days, but FORTH is a still a great fit for small micros, and has been ported to many.

For most simple projects, my preference would be to use a small flash-based micro like Atmels' TinyAVR or Microchips' PIC12F629. Both families have a large following, and plenty of info is freely available on the Web. An inexpensive in-circuit programmer can be made with your PCs' parallel port.

I need to update my micro setup (still using 8051's , have dabbled with PICs and AVR) and this is the path I'm taking. I think the baggage that comes along with micros is worth the trouble. Instead of stocking dozens of different TTL and CMOS parts, a single (and easily re-programmable, for those of us who make mistakes :shock: ) generic chip can often suffice.

I also check the surplus outlets often, sometimes you come across amazing bargains. I use the DK catalog for quick price checks and it's a good barometer of which parts are popular (<$) and which are going obsolete. Prices are ridiculous for some parts, others are quite reasonable ($1 for the PICF629/qty 25 is pretty good).

As far as timing accuracy, 32Khz makes a good tradeoff between accuracy (they're watch Xtals after all), low cost (ditto) and low power consumption. Micros aren't any more or less accurate than TTL/CMOS dividers, both use a similar chain of divider stages. You may be thinking of software timing loops vs. using a micro's internal timer to trigger an interrupt. It's the second method I was talking about. Most micros these days contain at least one hardware timer, sometimes with an optional pre-scaler on the front end.

The oscillator is the key to timing accuracy, and one of the better schemes I've seen implemented on some of the RTC chips is to bring out the 1-second tap. Then you can trim the oscillator capacitor to get a more or less "exact" 1 second period. You can do the same thing with TTL/CMOS or micro's.

Of course, not everyone using this board has ready access to an inexpensive micro setup, and TTL/CMOS will be around for a long time to come.

- CAL

(This post probably belongs in the PIC micro section, but then it just feels like preaching to the choir)

#### pixi

##### New Member
i dont have this"4536, 4060, 4020, and 4040" but i cat easily get it.
can y paint or do u know were i can get a ciruit for this??

#### laroche73

##### New Member
schematics

Yes, if you can wait until next week, I'll post some schematics and a description of how the circuits work. Get a few 4536s or the 4060 and a 4020. The 40x0 counters bring out most of their intermediate outputs, which helps in the decoding process. The 4536 has a single output, and requires a different approach. I only have some of the 40x0 counters in my junkbox, so the 4536 idea will be untested...

you'll also need some generic gates for the decoding, I hope you have a few XOR, & NAND or AND gates in your junkbox. You will also need a 32Khz crystal.

- CAL

#### nettron1000

##### New Member
Pixi, mind if i ask what the 32 hour interval timer is for ?

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