On Sunday, September 3, 2017 at 12:59:25 AM UTC-7, Cory Geesaman wrote:
The subject pretty much says it - I'm trying to find a (hopefully cheap - under $200) Arduino or RaspberryPI compatible photospectrometer which can be submerged for long periods of time in water to log water quality. I've been searching around a bit and can't find any, but if someone knows of one which could be hacked fairly easily (sticking it in a new case for instance) that would be great too. I'm not too worried about calibration (I can calibrate the thing and write the code needed to identify different ions from a bunch of data,) just want to avoid having to designed the thing from a capillary tube up though light sources and sensor if at all possible.
You are requesting a device which can:
1. be submerged => it must be physically small and self-contained
2. operate for long periods => it must be power efficient (i.e. likely battery powered, also sometimes incorporating solar)
3. log data obviously with timestamp, for long periods => it must have large storage memory
Both arduino and raspberry pi are completely unsuitable for #1, & #2, and arduino is unsuitable for #3. Neither arduino nor raspberry pi are power efficient, in fact the raspberry pi is a ridiculous power hog (including the zero). Arduino as a logger is only suitable for connected-pc operation, USB connected, not self-contained.
Logging data with timestamp (even deltas) is storage intensive over long periods. Usually the logging period is a compromise between storage size and required sampling rate for good data analysis.
I suggest starting with the single requirement "for long periods of time" and define exactly what that period is, calculate the storage requirement for that period, then use that to narrow the choices. Based on that period you can also calculate the total power required for sizing a battery, and then get an idea of total physical size (approximate) for a case design. A good board design should use no more than 50 mA average, especially considering it should be sleeping in between each data sample. Using all this info, you can filter through the available hardware to find the one that physically fits, will actually run for the given time, and be able to store the data between in-field downloads. Then narrow down to hardware which can run micropython if you want to avoid the assembly language programming.
There are several recent projects for water/environmental sampling such as some new oceanographic buoys off southern california, battery powered and recharge on solar. They might be using low power FSK radios to transmit data periodically to a shore station. Nordic semiconductor has some great boards which fit those types of applications.
--
## Jonathan Cline
## jcline@ieee.org
## Mobile: +1-805-617-0223
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