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A practical method for calibrating NTC thermistors
3 days ago • 0 commentsMuch of the existing information on sensor calibration assumes a certain level of pre-existing equipment/capability. This creates a chicken & egg problem with white-paper procedures targeting an accuracy that can not be obtained unless all the supporting parts of the system meet or exceed that same specification. This is almost never the case in educational contexts where STEM instructors often pay for classroom materials out of pocket. This mismatch parallels the situation twenty years ago when audiophiles dismissed the early MP3 players because they sounded so crude, completely missing the point that regular people were using them while jogging through downtown traffic. They were a good enough solution to a problem that didn’t need anything better.
From the beginning our project has been developing DIY logger solutions with that kind of 80/20 point in mind, and this thermistor calibration procedure hits that mark: https://thecavepearlproject.org/2024/04/20/a-practical-method-for-calibrating-ntc-thermistors/
To my knowledge this is the first time anyone has used the water freezing process to calibrate thermistors, rather than the melting point of an ice slurry.
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IR transmission through the falcon tube housing
12/14/2023 at 18:30 • 0 commentsAnother hidden gem: the polypropylene those centrifuge tubes are made from transmit IR frequencies opening up several sensor possibilities. PIR detection through the housing reaches about 5m for people. The loggers can also be triggered by animal traffic, so pet behavior is a popular theme for final student projects.
https://thecavepearlproject.org/2023/12/01/the-e360-a-classroom-data-logger-for-science/ -
0.49" micro OLED screens are remarkably low power
12/11/2023 at 17:06 • 0 commentsA hidden gem with our new e360 classroom loggers: the 0.49” micro OLEDs only draw about 3-400 µA and sleeps ~6µA! So you can have screen output like this for about same amount of power as an indicator LED and that means you can run them on a Cr2032! Since they use SSD1306 controller they can be made to work with standard libraries provided you compensate for mis-match between the origins on screen and the origin in the controllers 1K memory.
https://thecavepearlproject.org/2023/12/01/the-e360-a-classroom-data-logger-for-science/ -
The e360: A Classroom Data Logger for Science
12/01/2023 at 21:03 • 0 commentsWell it's been a long road, and several remote runs of the instrumentation course during COVID didn't help the process because they had to be done without soldering. But I think we've finally arrived at an educational version of the ProMini based logger that has the right mix of software and hardware adaptability to be a real contribution to other STEM educators . After a practice session soldering header pins to perf-board, students can build these and actually deploy them out in the real world. Two breadboards make it easy to align connections with the many different I2C sensor modules on the market provided they aren't too demanding for the little Cr2032 that powers the unit. Memory expansion is nearly effortless with 32k EEprom modules. At between 5-10uA sleep current with those cheap sensor modules attached, you should easily get at least 6 months of operation.
https://thecavepearlproject.org/2023/12/01/the-e360-a-classroom-data-logger-for-science/The software is now much more streamlined compared to what we released in 2022, and we moved the LED / sensor cluster around to accommodate the lab activity sequence:
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Testing Cr2032 Batteries with our 2-Part Mini loggers
06/05/2023 at 19:55 • 0 commentsRan a series of Cr2032 battery tests with our 2-part falcon tube loggers and was pleasantly surprised to find that even with the default BOD limiting us to the upper plateau of those cells; we can still expect about two years of run time from most name-brand batteries. https://thecavepearlproject.org/2023/06/05/testing-cr2032-battery-discharge-time-with-our-2-part-promini-loggers/
With a series of resistors on the digital pins, this little logger might be the easiest way to simulate duty cycles for other more complex devices that you can’t afford to lose a dozen of for the duration of long term tests. Also note the curves are a bit chunky because the internal vref trick only has a resolution of 11mv, and we use index compression that reduces the record further to 16mv/step.
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A DIY Pressure Chamber to Test Underwater Housings
05/25/2023 at 16:00 • 0 commentsThe max depth for conventional scuba diving 130 feet - 40 meters - as dives to those depths can usually avoid complicated decompression procedures. This also covers the vast majority of underwater research deployments, and our work is focused there with our little falcon tube loggers. In keeping with the projects 'hardware store' ethos, household water filters offer a good solution for pressure testing DIY builds for deployment in that zone without blowing the budget:
https://thecavepearlproject.org/2023/05/24/a-diy-pressure-chamber-to-test-housings/ -
2-Module Mini Logger Build Tutorial (w 64k EEprom upgrade)
04/25/2023 at 14:47 • 0 commentsThe latest in an ongoing series of build videos supporting Dr. Beddows enviro-sci students who all have to first build the logger(s) that get used for their final research project. These videos also support the other instructors who have adopted our DIY loggers for their own courses. These Falcon tube mini-loggers may well be as minimal as it is possible to go while still offering the flexibility of supporting multiple different sensors. About the only limitation is that the CR2032 levels out at 3.0v and runs all the way to 2.8v before shutdown - which rules out some older sensors like the DS18b20 which has a lower limit of 3.3v. After calibration, the NTC has so much more resolution that it’s not much of an issue.
And for those with more build experience we also posted a 4minute 'rapid review' of the steps:
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Insights from a Decade of Tipping Bucket Rain Gauge deployment
04/17/2023 at 14:59 • 0 commentsI know these janky installations will have the weather nerds out there inhaling through their teeth, but it’s worth noting that we made multiple attempts over the years to do things the ‘right way’ that just kept failing to go the distance. Even in a harshest environment, critters are the biggest threat to actual ‘boots on the ground’ research - both four & two legged. So our rule of thumb for anything that’s going to last is: “Make it ugly & make it heavy”
https://thecavepearlproject.org/2023/04/15/insights-from-a-decade-of-tipping-bucket-rain-gauge-deployment/ -
Waterproofing your Electronics Project
03/17/2023 at 18:34 • 0 commentsI know most Hackaday builders have already worked their way through these issues, but we keep getting calls from researchers new to the game. So I produced a nice summary for them of the waterproofing techniques we’ve used over the years. Hopefully there’s one or two ideas in this post that folks here find useful. Cheers!
https://thecavepearlproject.org/2023/03/17/waterproofing-your-electronics-project/ -
Powering our ProMini logger for One Year on a Coin Cell
03/10/2022 at 15:57 • 1 commentIt’s been a long time since I posted, and you’d be forgiven for thinking the Cave Pearl Project was yet another victim of COVID. While the attendant travel restrictions did require replacement of entire field deployments (due to battery leakage) we are still very much alive & kicking. Several sensor development & student projects are on a slow burn, but unfortunately that also involves a ‘soft embargo’ on the newest toys until certain students finish their papers...
Anyway, at this point we’ve proven that it IS possible to teach a ‘hands on’ instrumentation courses over zoom. Though that required removing soldering from the labs - something which is highly suboptimal from a fieldwork perspective. Other teachers stepped into the breach with us, and with feedback about their time & budget limitations we've developed a new 2-Part ‘EEprom only’ version of the logger which handles all download & control through the IDE’s serial monitor window. Unix timestamps are reconstituted from the record number during download which means none of the limited storage space gets used for that predictably repeating sequence.
A typical sleep current below 5uA means this new data logger will easily run for a year on the CR2032 backup coin cell that’s already attached to the RTC module, and unlike just about every other low-power Arduino project we haven’t used custom fuse settings or bootloaders to lower the BOD. With a 220uF tantalum buffering the rail none of that annoying confabulation is necessary. Add a couple of cheap 32 or 64k EEproms and you have the perfect platform for low power sensor ICs like the BH1750, BMP280 or the SiLabs7051. This may well be as minimal as it is possible to get and still offer beginner level students an opportunity to develop their own final projects.
https://thecavepearlproject.org/2022/03/09/powering-a-promini-logger-for-one-year-on-a-coin-cell/