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Forum Index : Microcontroller and PC projects : Hi Accuract RTC for MuP, BP170 and others
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bigmik Guru  Joined: 20/06/2011 Location: AustraliaPosts: 2870 |
Hi All, I have found a neat little RTC module that uses the High accuracy (quoted at less than 0.4sec per day) Real Time Clock Chip that `almost' looks as though it was designed with my `Mik-Standard' I2C layout in mind.. (as used in MuP and BackPack170) Here is an ebay link to the modules. eBay Link At $1.87AUS that is really quite amazing, considering they use a DS3231 RTC chip which is the big brother to the DS3232 that I used in my SMDBackPack170 board (That chip alone in 1 off is around $12eaa) All that is needed to plug into my `Mik-Standard' I2C bus is to run a short wire (red in the following pictures) from Pin 1 to Pin 4 of the 5 pin female header and offset the module when you plug it into the I2C 4pin header so that pin 1 is hanging over as shown below. 
The Pinout of the Module is as follows: 
As can be seen pin 4 has no connection and this mates up with `Mik-Standard' for I2C power (set to 3v3) and every other pin lines up... The short link transfers the power to where the module expects it to be on pin 1. I have had it running now for about 2 weeks and (after synchronizing my PC to internet time) it had lost about 2seconds in 2 weeks. Not a bad $2 investment and of course can be adapted to any other I2C pinout. Regards, Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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| paceman Guru Joined: 07/10/2011 Location: AustraliaPosts: 1328 |
Wow, how 'bout that Mik. Maybe Peter should use the layout for that module on his new board - battery is there too! |
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MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209 |
Is that a 1992 week 6 chip? Or does it mean something else? Microblocks. Build with logic. |
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| bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2870 |
@Greg, Yes I did think that .. Which is what prompted me to first post this thread. @TZ, I would have to look at the datasheet but my guess would be not that old. Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 5922 |
My interpretation of the date code is week 26 of '09 Jim VK7JH MMedit  MMBasic Help |
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| HankR Senior Member  Joined: 02/01/2015 Location: United StatesPosts: 209 |
The DS3231 I believe was introduced in 2005 by Dallas Semiconductor. The DS company was already owned by Maxim at that time. Hank |
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| MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209 |
Yes week 26 of year '09 makes more sense. Lots of these modules on ebay have parts that are salvaged (recycled  ) from old pcb's.
I have seen them do it here too in Thailand. Girls with heat guns.:) Just apply heat until the parts fall off is the criteria. Not my favorite source, but for a few single parts it is fine. Microblocks. Build with logic. |
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| HankR Senior Member Joined: 02/01/2015 Location: United StatesPosts: 209 |
The original datasheets for the DS3231 and DS3232 were issued January and September respectively, of 2005. |
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Zonker Guru Joined: 18/08/2012 Location: United StatesPosts: 761 |
Just got 10 of these RTC's Have one running on the GCmicroboard2... Seems to be running fine... I like this IC because the X-tal is inside... Add a battery, good to go... |
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| paceman Guru Joined: 07/10/2011 Location: AustraliaPosts: 1328 |
Just ordered myself a few too - thanks for the link Mik. Greg |
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OA47 Guru Joined: 11/04/2012 Location: AustraliaPosts: 911 |
Thanks for the heads up bigmik, just ordered some too  |
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| piclover Senior Member Joined: 14/06/2015 Location: FrancePosts: 134 |
0.4s per day is 12s a month... Not that good an accuracy (it's the base accuracy of any low cost quartz watch). With a PCF8563, a 32KHz quartz and a 30pF adjustable capacitor, I managed accuracies better than 3s a month in several projects I made. Of course, you need to manually tune the capacitor, but it results in a 4 times better accuracy (which could further be increased, with a temperature monitoring and computed correction according to the measurements). |
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| Chris Roper Senior Member Joined: 19/05/2015 Location: South AfricaPosts: 280 |
Or just add a Rubidium atomic timebase. It may increase the cost slightly above the $2 mark, however 
Cheers Chris http://caroper.blogspot.com/ |
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f1fco Senior Member Joined: 18/03/2012 Location: FrancePosts: 154 |
just to laugh, a little calculus : $2 : DS3231 : 0.4 / 86400 ~ 4 x 10-6 accuracy it is the "reference" $3 to 5 : PCF8563 + xtal + ajustable : 0.1 / 86400 ~ 10-6 accuracy price x2 for x4 of accuracy $150 to 200 : Rubidium frequency standart(on ebay) ~ 10-10 to 10-11 accuracy price x100 for x10000 to x100000 of accuracy I use also a GPSDO (from DF9NP, a German hamradio) http://www.df9np.de/page3.html a VERY HIGH accuracy : the atomic clock of GPS sats... (Cesium ?) Pierre, F1FCO, from Nimes, south of France 73s de F1FCO |
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BobD Guru Joined: 07/12/2011 Location: AustraliaPosts: 935 |
Mick, If you want better accuracy than that, it is probably possible. Register 16 (&H10) of the DS3231, DS3232, & DS3234 can be used for trimming the accuracy. It adds or removes trimmer caps to the onboard timing capacitance. Because it's onboard it is also temperature compensated. Below is a partial quote from page 14 of the datasheet. [quote] The crystal aging offset register provides an 8-bit code to add to the codes in the capacitance array registers. The code is encoded in two’s complement. One LSB represents one small capacitor to be switched in or out of the capacitance array at the crystal pins. . . . . . . . Positive aging values add capacitance to the array, slowing the oscillator frequency. Negative values remove capacitance from the array, increasing the oscillator frequency. The change in ppm per LSB is different at different temperatures. The frequency vs. temperature curve is shifted by the values used in this register. At +25°C, one LSB typically provides about 0.1ppm change in frequency. [/quote] I experimented with it and found it did the job but you would only use it in situations of need for great accuracy. I've never found it to be necessary but it sounds like your one is a slight bummer. You should ask for your money back. |
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| twofingers Guru Joined: 02/06/2014 Location: GermanyPosts: 1139 |
Just for information purposes (regarding accuracy): I use a 1$ DS3231 module from china and compared with a radio controlled clock is there a difference of one second after four month. |
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| WhiteWizzard Guru Joined: 05/04/2013 Location: United KingdomPosts: 2794 |
. . . but where did you buy the clock from? 
I had a 'cheap' radio tuned clock once that never latched onto any signal no matter what you did with the aerial. Realised this after only two days when it had drifted by over 1 minute (from the TV news broadcast). As a potential solution to others out there; I now use a GPS module connected to a RF Tx module to act as a local timer-server in the house. Then each MM clock I have around the house simply has a RF Rx to pick up this time signal. Using UK licence exempt 868MHz to get better range than 433MHz. WW For everything Micromite visit micromite.org Direct Email: whitewizzard@micromite.o |
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| twofingers Guru Joined: 02/06/2014 Location: GermanyPosts: 1139 |
I don't know. It is a very old clock (I have more than ten). I guess I've bought the clock 20-30 years ago. Maybe from "Conrad Electronics" (a german company). 
Do you think there could be any influence on the DS3231 module? (The older the radio controlled clock the better the accuracy of the DS3231?) ... just kidding.
Regards Michael |
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