DS3231 vs DS1302 for drift over time?
xanatos
Posts: 1,120
I notice that the clocks in many of my field projects that use the old DS1302 chips drift about 2 or 3 minutes a month. These projects are not near wifi or any ability to poll NIST, so they have to be standalone. While I give the users a very simple keypad entry time setting function, I'd rather that they don't need to set them every few months.
The DS3231 looks like it has much greater stability... does anyone here have any experience with that chip? Thoughts as to it's performance over the old DS1302?
Thanks!
The DS3231 looks like it has much greater stability... does anyone here have any experience with that chip? Thoughts as to it's performance over the old DS1302?
Thanks!
Comments
I had the same problem with my 1302 clocks as well. Thought about find another chip that`s more stable, but ended up with a simple solution; I made a simple routine that runs once a day (03.00 at night) that set the 1302 clock back 14 seconds. That because I figured out that the clock went abt 14 sec too fast pr 24h. Now my DS1302 has been fairly close to right time for 2 months. Simple way to by-pass a problem... , and you don`t have to do any hardware changes. This could maybe work for you, if you dont have to have "on the second" right time all the day through?
The only real problem is that they are all surface mount parts in 16 and 20 pin packages. This means that board layouts have to be changed if you want to switch. There is one part, the DS3231M, which is available in an 8 pin SOIC. It uses a MEMS oscillator instead of a crystal and is 5ppm vs 3.5/2ppm for the crystal oscillator versions. It's I2C only, no SPI version.
I made the mistake of buying some DS3231's from eBay and not a single one keeps accurate time (worse than the worst of any DS1302). On the other hand, all of the chips purchased from Mouser only lose/gain a couple seconds a month.
Kenny