RTC Selection Suggestions?

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We've been using Maxim/Dallas DS1305/DS1306 RTC in many apps over the past 8 years or so. It works fine for us, and I've got all my proven "drivers" to set time, etc. It uses SPI interface.

A new design is on the drawing board. Does anyone have any compelling alternatives? Cheaper is better. ;) (lessee--DigiKey qty. 100 price is US$2.29) I prefer SPI 'cause I have the pins and I'm not a big I2C fan.

What is your favorite?

Lee

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Good question, Lee. I've been using the DS1306 for a long time now (and also prefer SPI to I2C). I'm also interested in answers to your question.

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Check out the Epson line. I have used them before, but they are parallel only. Might not suit your needs

I think Maxim has some as well

Jim

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It's slightly more expensive, but what about the DS3234? With it, you don't have to add your own crystal or caps, saving part count and board space... in volume, about 70 cents more, but a good portion of that would be made up just in the savings by eliminating the crystal.

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Quote:

Good question, Lee. I've been using the DS1306 for a long time now (and also prefer SPI to I2C). I'm also interested in answers to your question.

First pass results:

--The $2.29 is quite a bit less than we paid 5-8 years ago, so is not a killer.

--The DS1305/6 package is not tiny but is OK.

--Requires external crystal

--The battery that we use Panasonic BR1225 3V lithium 40mAH costs ~$1.50.

So with crystal it is about US$4 in parts cost.

Dallas has a newer and less expensive series DS1390, ~$1.50/100. It has provisions for trickle-charge of a backup battery or supercap, but why fuss with it when the supercap costs about the same and is the same size as the battery? (and it has no SRAM but I've only used that on one app)

Lee

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Quote:

It's slightly more expensive, but what about the DS3234? With it, you don't have to add your own crystal or caps, saving part count and board space... in volume, about 70 cents more,

You've lost me. DigiKey qty. 100 pricing is $4.67, or 2x a DS1305/6. And the 32k crystal is cheap.

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Silly question but can't you make an RTC solution with an Xmega alone and put the $2.29 towards the cost of that AVR?

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Hmmm--in this app I don't want to try to keep the whole app sleeping. But a Mega48 w/32k crystal and Vcc-diode+(to AVR)+diode-battery like we have on another app...

Xmega has too many rats err errata right now, and the cheap ones aren't out yet.

For, say, 100 units/year the dev costs may not be worth it. But an interesting alternative.

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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theusch wrote:
Quote:

It's slightly more expensive, but what about the DS3234? With it, you don't have to add your own crystal or caps, saving part count and board space... in volume, about 70 cents more,

You've lost me. DigiKey qty. 100 pricing is $4.67, or 2x a DS1305/6. And the 32k crystal is cheap.

I was looking in larger quantities. Sorry. :(

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Again revisiting this topic (another new app on the drawing board), Seiko S35390 is I2C interface, and costs a little less than $1 (DigiKey $0.88/qty. 100).

Anyone have any experience with that part, or can suggest other competitive choices?

Lee

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Lee

How about the offerings from Intersil?

Randy

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Looks good, Randy--near the $1 price point of the Seiko, and in addition has the separate VBAT pin eliminating external diodes and the like. On-board analog (capacitance) and digital (temperature) compensation.

Do you apply them? What 32k crystal do you use?

Lee

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Lee

I've only sampled them, haven't used them yet.

Had plans to make my own alarm clock, for "learning purposes" :roll: So far, the samples are still in their baggy. I picked up some 32KHz xtals from either futurlec or goldmine. I also got a sample of a couple of the 32KHz offerings from Maxim that are supposed to be more stable.

Randy