Re: Accurate clocks: DS1307 vs. ChronoDotPostby JBeale » Fri Sep 16, 2011 12:52 pmfrom http://datasheets.maxim-ic.com/en/ds/DS1307.pdf"CLOCK ACCURACYThe accuracy of the clock is dependent upon the accuracy of the crystal and the accuracy of the match between the capacitive load of the oscillator circuit and the capacitive load for which the crystal was trimmed. Additional error will be added by crystal frequency drift caused by temperature shifts."The datasheet as far as I can see, makes no claims about actual accuracy of the clock, reasonable since it's up to the user's circuit to insure correct crystal and matching caps.By contrast, the DS3231 chip in the ChronoDot has its own crystal and caps internally, so they have control over the complete timing circuit and can make a specific claim about accuracy (+/-2 ppm over 0-40 C).http://pdfserv.maxim-ic.com/en/ds/DS3231.pdf
A further metric is that by internal monitoring of the hive temperature you can estimate brood size (amount of new bees being raised). This requires a HUGE amount of temperature sensors to be installed within the hive. Here's where the feasibility problem and issues comes in. I'd be looking at the temperature sensor Texas Instruments TMP275 which allows for up to 8 sensors to be tied together within a bus. If we go with 8 sensors per frame, 10 frames per box, we'd be looking at 80 sensors per brood box, and the hive can eventually have 3 or 4 brood boxes once mature. So 240 to 320 temperature senors would need to be captured from 30 to 40 data buses each with 8 sensors.
How much variation do you expect across these sensors? That seems like overkill, at least to a non-beekeeper.
afremont, thanks for taking the time to look over my proposal. I'm expecting to know if I get my full grant or just partial funding (which probably can't support 3D temp profiling, where full would) by the end of the month. I'm going to need assistance in designing circuits, or boards. I have some help already but any and all people who want to help with the project is welcome. I want to keep this thread going with updates as we go and all relevant circuits, boards, files and code to help anyone else who wants to do what I'm doing.I agree that bees definitely need studying, they're EXTREMELY important for the health of our plants, ecology and us! Plus even if this isn't ground-breaking research, its good for undergraduates to learn the process of experiment design, data collection, and analysis. ;-)With the sensor it should have a variance of 0.5C, correct? Would calibration of each sensor help? Is each off a specific amount that could be corrected if you knew the offset? Or is it random/variable?Ultimately the range I'm looking for is 33-36C or 34-35C. It's a fairly narrow range, but it's not fractional of a degree but whole degrees. Obviously I need high precision sensors, but I can't afford EXPENSIVE sensors. The $1/sensor range is about my limit.