Real time clock options for use with Beaglebone?

[Andrew Frazer]

I need to be able to keep track of the 'real' time between system restarts.  My system needs to be stand-alone,  and has no visbility of any NTP servers, so it seems to me that a RTC is really the only option for me. Its a pity that there is no battery backed up clock on teh beaglebone, but thats life.  You can't have everything.  

An option i am considering is adding a simple DS1307 on the I2C bus.. Very similar to what was suggested at

http://learn.adafruit.com/adding-a-real-time-clock-to-raspberry-pi/set-rtc-time

Does anyone have any other suggestions..

[Andrew Bradford]

DS1339, since it's available in 3.3 V power and I/O.
Works well for me.

-Andrew

[Eric Fort]

DS3231/DS3232 or DS1337C (the SO16 not the 8 pin version) are what I'm looking to implement for my RTC's across the board.  both have integrated crystals making them really easy to use (just attach power, ground, SCL, SDA, & backup battery, and load the kernel module).  The DS3231/DS3232 is a TCXO so it keeps slightly better time but the DS1337C is just well 1337...  Take your choice, both are great options requiring only the attachment of an external backup battery and the I2C bus.

Eric

 
 

[Eric Fort]

actually after looking at it again the ds1337/ds1337C has no means of attaching a backup battery.  while a super cap might be an option, a part with provision for a real backup battery seems like a better option making the DS1337C not so 1337 after all!

Eric

[Andrew Bradford]

On Tue, 22 Jan 2013 17:33:13 -0800

Eric Fort <eric...@gmail.com> wrote:

> On Tue, Jan 22, 2013 at 2:39 PM, Eric Fort <eric...@gmail.com>
> wrote:
> > On Tue, Jan 22, 2013 at 12:33 PM, Andrew Frazer <
> > andrew...@stellascapes.com> wrote:
> >
> >> I need to be able to keep track of the 'real' time between system
> >> restarts. My system needs to be stand-alone, and has no
> >> visbility of any NTP servers, so it seems to me that a RTC is
> >> really the only option for me. Its a pity that there is no battery
> >> backed up clock on teh beaglebone, but thats life. You can't have
> >> everything.
> >>
> >> An option i am considering is adding a simple DS1307 on the I2C
> >> bus.. Very similar to what was suggested at
> >>
> >> http://learn.adafruit.com/adding-a-real-time-clock-to-raspberry-pi/set-rtc-time
> >>
> >> Does anyone have any other suggestions..
> >>
> >>
> > DS3231/DS3232 or DS1337C (the SO16 not the 8 pin version) are what
> > I'm looking to implement for my RTC's across the board. both have
> > integrated crystals making them really easy to use (just attach
> > power, ground, SCL, SDA, & backup battery, and load the kernel
> > module). The DS3231/DS3232 is a TCXO so it keeps slightly better
> > time but the DS1337C is just well 1337... Take your choice, both
> > are great options requiring only the attachment of an external
> > backup battery and the I2C bus.
> >
> >

> > actually after looking at it again the ds1337/ds1337C has no means
> > of
> attaching a backup battery. while a super cap might be an option, a
> part with provision for a real backup battery seems like a better
> option making the DS1337C not so 1337 after all!

DS1339C-33# is what I use. 3.3 V power and I/O, integrated
crystal, and powered via a linear regulator from the SYS5V source
(but can also take a super cap or coin cell). When the bone's off, if
you have a lithium battery connected to the TPS65217, SYS5V stays
present but at battery voltage. This allows keeping of time without a
coin cell if you use a lithium battery to power the bone, too.

-Andrew

[Eric Fort]

Thanks for the mention of the DS1339C - Does everything I'd need from the 1337 and adds battery backup.  Nice chip.  Now in choosing between a DS3232SN# and DS1339C it's Down to price vs timing accuracy ±2 ppm or ±10ppm, ah the ole how good do you want/need it to be and how much does it cost!

Eric

[Gregg Harrington]

I am considering doing the same. However after running:

modprobe -l | grep rtc

I don't see any RTC modules. Is there an opkg install needed?

[Andrew Bradford]

On Mon, 28 Jan 2013 23:11:22 -0800 (PST)
garre...@gmail.com wrote:

> That 10ppm is a lot worse than it seems...it's the rating at a steady
> 25C. When the temperature varies, it's going to go WAY off the rails.
> The DS3231's 2ppm is rated across the chip's entire temperature
> operating range. In practice, and in varying temperature conditions,
> there's just no comparison.

10 ppm is about 5 minutes per year. 2 ppm is about 1 minute per year.
That's pretty decent.

Yes, the DS1339 and similar RTCs have an error curve that depends on
temperature, as seen in [1], so if wide temps are important to you it's
definitely worth understanding that curve.

[1]:http://www.maximintegrated.com/app-notes/index.mvp/id/58

The DS3231 is a better RTC. But if you compare any RTC with no RTC,
any RTC is better, too :)

At really cold temperatures the batteries (assuming you don't use a
super cap) powering the RTC are going to suck anyway. But again, going
battery vs super cap is another trade off since batteries can hold
quite a lot more energy than a super cap of the same physical size.

My desire for an RTC is to keep close to the correct time if the
product sits on a shelf for 1 or 2 years. Close means we're reasonably
accurate and that every boot is correctable by ntp if it's available.
Having a board think it's the year 2000 is bad, but having the clock
off by 10 minutes isn't a problem for me. If your application is
different, the DS3231 might be a better choice or some other time
keeping mechanism might even be a better choice than that.

It's all trade offs, there's no right answer.

-Andrew

[Gökhan Tarim]

I think you could see this web site : http://www.mcu-turkey.com/beaglebone-ile-ds1307-kontrolui2c-uygulamasi/

22 Ocak 2013 Salı 22:33:58 UTC+2 tarihinde Andrew Frazer yazdı:

[Andrew Frazer]

The DS3231it is. Its a bit more expensive, but my app certainly won't be at a nice stead 25C!!!

On 29/01/2013, at 8:11 PM, garre...@gmail.com wrote:

That 10ppm is a lot worse than it seems...it's the rating at a steady 25C. When the temperature varies, it's going to go WAY off the rails. The DS3231's 2ppm is rated across the chip's entire temperature operating range. In practice, and in varying temperature conditions, there's just no comparison.

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[Juanjo]

It seems to be Turkish. Google Translate may help you ;)

On topic, I've using DS1339-33 with it's respective XTAL and Lithium Cell battery; works a charm an Linux as the drivers in it. Don't need much of resolution since I do sync with NTP once in a while so by now I'm using a 20ppm XTAL.

Just follow the App Note and connect it to i2c2 

On Saturday, June 1, 2013 2:41:26 AM UTC-4, ehi...@gmail.com wrote:

Unfortunately, the link is to a website written in Klignon...

[Carl James]

I see this is an old thread but as its still a recurrent question for BeagleBone users I thought I'd chip in...

The SanCloud BeagleBone Enhanced WiFi 1G + RTC is a pin-to-pin compatible enhancement of the BeagleBone Black. It comes with an integrated RTC board including a CR2032 battery and/or supercap (user modification) option. The SBC can be purchased with an onboard antenna or support an external antenna. A product summary page is here: https://www.sancloud.com/beaglebone-enhanced-bbe and each of the different board variants can be seen /purchased from the online store at https://www.sancloud.com/store