Well, I prefer the DS1302 ... because of the trickle charger.
BTW. I put a 1000 uF cap on pin 8 ... configured the trickle charger with one diode and a 2k while operating on 3.3v ... result:
After loading the current date and time ... removed power and checked the clock the next morning. the RTC ran from 9:30pm to 3:37am (roughly 6 hours).
The chip still had the date and time (just locked at 3:37am), and all the ram variables too. Can I assume, that as the power dwindles "the chip stops advancing the clock"
What size cap should a super cap be? (to keep the time for about a week)
Tim: I have no idea how long a 1000uF cap would last. A low leakage cap is required as I would expect the power required fot the RTC is tiny. If you have a meter, measure the voltage on the cap each day and see when it gets to the minimum value required by the RTC. This will give you an approximation only as proper calcs need to be done. I am interested in what you find. IIRC the DS1340C is capable of trikkle charging too. The socket and 1125? coin cell is quite cheap, but it does take space.
That was the biggest cap I had laying around. Hey, an idea just formed in my head (boy is that rare). What if you preformed the same test with a mystery sized cap? Could you equate size by comparing times till the counter stopped?
Lets see ... 1,000 uF cap lasted 6:07 (6 * 36000 + 7 * 60) or roughly 22,000 secs.
Unfortunately, you cannot guaranteed each chip to be the same as the next. However, the big variation is in the cap which has possibly a +20%/-80% variation. Anyway, it is unknown what the RTC will do when the voltage drops too low. The date/time maybe corrupted.
Unfortunately, you cannot guaranteed each chip to be the same as the next. However, the big variation is in the cap which has possibly a +20%/-80% variation. Anyway, it is unknown what the RTC will do when the voltage drops too low. The date/time maybe corrupted.
I've made several tests now ... and in each case the clock stopped running apx 6 hours after I power down the board. Yet my RFID keys (I have 2 stored in RAM) remain in tact. The time shows when the 1302 stopped advancing the time values stored. And the date is valid!
I'm wondering if the chip has 2 low power modes? That would seem to explain the results I'm getting. The chip stops counting .... but continues to hold the RAM values? Even 24 hours after the counting ceases! I can power up and read the RAM values.
I have a ChronoDot (DS3231) and am having trouble getting it to work with the Propeller. I have clock on 28, data on 29, pullups (10K) to 3.3 on both. I downloaded the DS1307_RTCEngine object and tried it with no luck. I also tried the i2cObject and it is not found. I tried both the default )xD0 and the ChronoDots 0x68. Is there something I'm missing? It works fine on an Arduino so I know the device is working.
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But otherwise, the uSOP8 would be the next choice.
Cluso, Why the DS1340? Looks like you trade the alarms of the DS1339 for a programmable output.
BTW. I put a 1000 uF cap on pin 8 ... configured the trickle charger with one diode and a 2k while operating on 3.3v ... result:
The chip still had the date and time (just locked at 3:37am), and all the ram variables too. Can I assume, that as the power dwindles "the chip stops advancing the clock"
What size cap should a super cap be? (to keep the time for about a week)
Lets see ... 1,000 uF cap lasted 6:07 (6 * 36000 + 7 * 60) or roughly 22,000 secs.
... Tim
I've made several tests now ... and in each case the clock stopped running apx 6 hours after I power down the board. Yet my RFID keys (I have 2 stored in RAM) remain in tact. The time shows when the 1302 stopped advancing the time values stored. And the date is valid!
I'm wondering if the chip has 2 low power modes? That would seem to explain the results I'm getting. The chip stops counting .... but continues to hold the RAM values? Even 24 hours after the counting ceases! I can power up and read the RAM values.