Real Time Clock Hardware

I need to put a real-time clock on a board. I haven't needed to know anything about the market for this for years, and I see that I'm way out of date.

I just need basic clock functionality that I can read and set under software control, I don't need any bells or whistles, and I don't care much about the format.

What I do care about is something that I can put on the board easily and will work reliably.

I could put a chip, caps, crystal and battery on the board. I see the

24-DIP sized chips that come with the flip-top, though, and they look like I could short-cut a number of production issues by using them.

Does anyone have any experience with these things? Are the tops interchangeable, or do I have to use a TI top with a TI bottom, ditto for NXP, etc.?

Any other positive or negative relevant experience anyone wants to share?

Thanks.

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Tim Wescott
Wescott Design Services
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Tim Wescott
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Use DS1307

Vladimir Vassilevsky

DSP and Mixed Signal Design Consultant

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Reply to
Vladimir Vassilevsky

Do Dallas parts have the same ongoing availability nightmare associated with them that Maxim parts do?

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Tim Wescott
Wescott Design Services
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Reply to
Tim Wescott

This one is about as common as MAX232, so it should not be a problem at all.

VLV

Reply to
Vladimir Vassilevsky

Epsom has some dips with the crystal inside and all. Just add a lithium battery and you'll be good for 10 years, maybe 20.

John

Reply to
John Larkin

Maxim has the DS3231/DS3232 parts with a temperature compensated crystal. I am using the DS3231 on one of my boards and have been pleased with it. You do pay for the integration, however.

-Michael

Reply to
Michael

Hey Tim,

The DS1307 is a reliable choice and we use it here. Very straightforward one-wire communication, very good accuracy, etc... Can run on a crystal (32 khz), or the expensive (and very accurate) companion DS32KHz TCXO Also, straightforward to hook a backup battery, etc..

Note: If using the high stab osc., tucked away in a non-obvious app note somewhere is a caution to use a high value resistor between the two parts to avoid excessive current drain when operating on a coin cell. Be sure to review if you choose the 1307.

One drawback is that the 1307 requires 5-volts. If you have that avail, then no problem.

But if not, take a look at the DS32B35. (DS32C35) Maxim sent me a datasheet on this a while ago and I recall it looked rather promising. It should be in production by now?? We may switch to it.?

It was an "all-in-one" unit. RTC, TCXO time base, Non-Volatile memory, etc... Which means even though it has the bells and whistles, it might negate the need for hardware elsewhere. Was even or better on pricing than the 1307. Comes in a SO-20 package.

FYI - sometimes 1307's in DIP's can get scarce (which I suspect is due to RoHS?), but pretty soon that will likely be the case with all things DIP.....?

-mpm

Reply to
mpm

If cost is an issue, look at the JRC NJU6350. Cheap as dirt, tiny and we've not had any issues with it.

Reply to
Jim Stewart

We started having a tough time getting Dallas parts within a year of the Maxim takeover. I don't use any Maxim parts whatsoever.

-Hershel

Reply to
Hershel

Cost is an issue. With a projected 50/year volume, engineering cost trumps all. The less we have to mess with battery holders, crystal selection, operation at cold and hot, board layout and/or part selection difficulties -- the better.

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Tim Wescott
Wescott Design Services
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Tim Wescott

Isn't Epsom some kind of salt against swelling and soreness? SCNR...

One detail that might be of importance is how the HW side of the SW control for this RTC is going to be handled. SPI? I2C? Other?

Talking about high-tech here: Does anyone know where to get wax rope for making cable harnesses? Couldn't find it on Digikey or Mouser. Or am I just too freaking old?

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Regards, Joerg

http://www.analogconsultants.com
Reply to
Joerg

C is going to be handled. SPI? I2C? Other?

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last one if from Newark

martin

Reply to
martin griffith

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Ah, thanks! Didn't know it was called lacing cord these days. We used to call it wax rope or harness cord. Digikey is out but Mouser has that as well. They even got it in black, I only knew the white stuff. Cool.

10c/yard is kind of highish but those 500 yards will last a long time.
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Regards, Joerg

http://www.analogconsultants.com
Reply to
Joerg

They've recently invented these things called "tie-wraps."

Which reminds me to find some plastic spiral cable protector stuff to keep the cats from chewing up the cables on Mo's Mac.

John

Reply to
John Larkin

Do they have a tie wrap made out of string yet?

martin

Reply to
martin griffith

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Most aircraft supply shops carry Koroseal lacing cord. It's still used for behind- the-panel avionics lacing.

Reply to
Jim Stewart

There are 'odd' occassions, where using waxed cord is nicer (things like doing rewiring work on vintage equipment for example). Remember there is nothing 'special' about this cord. Waxed cotton thread is available from many suppliers. It is just not held by electronic companies now, since in normal use on electronics, it has been replaced by solutions like the wraps and ties mentioned. A search for 'waxed tying string', should find dozens of sources. Some aviation suppliers, also still offer this.

Best Wishes

Reply to
Roger Hamlett

Yeah but it ain't the same. Wax rope looks a lot more neat and tidy. To me tie-wraps have the curb appeal of a rubber band. Plus they crumple. Ok, I have used them on my LAN runs as well but only because I could neither turn nor see much in the crawl space.

A Mac? Gasp. I'll have to talk to one on the current project. Not really looking forward to that.

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Regards, Joerg

http://www.analogconsultants.com
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Joerg

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Aha! Cool. Because we have a local runway almost next to the house so I could waltz over there and see if they've got any.

I have seen

Reply to
Joerg

I'll bet they were either the cheap plastic ones, or natural nylon. The black ones are UV resistant, and last a lot longer. Outdoors, they outlasted natural nylon over 5 to 1, and that was up north, in Cincinnati, ohio. The additional UV in Florida kills the cheap ones even faster.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
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Reply to
Michael A. Terrell

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