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Question:What would be a good basic activity to test out a data logging device in water?

stevie asked on June 16, 2017 15:42
152 | 4 answers | shortlink

I'm looking to set up a few activities that people could try in testing out data loggers in the water. Some of the ones I’ve been thinking about are:

  • running them in a bucket of water,
  • two loggers in the same place, and
  • for something more field based, an upstream, downstream test.

Does anyone know of an activity posted or one that could be pulled together?

water riffle data-logging nano data-logger

question:riffle question:general question:data-logging


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4 Answers

Possibly some of the Coqui activities (which were designed for real-time monitoring, not data logging) could be adapted for a data logger?


Stevie, it sounds like you are looking for demonstrations of things data loggers can do. That really depends on what logger(s) you have and what sensors you have. Most of the loggers at the new wiki (https://publiclab.org/wiki/data-logging) can do all sorts of environmental data logging with all sorts of sensors. For unattended outdoor logging you need a weatherproof (or waterproof) enclosure and a system that will operate long enough for your needs. Then you need a sensor (or multiple sensors) appropriate to your demonstration.

Environmental data logging is not very exciting until you see the data. So the best demonstrations have radio feeds and the data is available live on the internet or some smaller network. Next best might be a portable display so some data can be seen as it is being saved (e.g., to SD card). Little LCD monitors cost just several dollars and turn a data logger into a data readout device (see this note: https://publiclab.org/notes/cfastie/05-03-2017/monitor-your-data-logger).

Most data loggers save barebones data files (just numbers and commas) so you have to work out a system for transferring the data to a computer and parsing them so they can be interpreted. There are ways to have data graphed or mapped automatically, but usually some human intervention is needed to make the data accessible to your audience. The data file is not the end product -- summarizing and presenting the data often takes more skill than writing the Arduino sketches that make the loggers work.

All of the microcontroller based data loggers run on batteries, so they can become portable environmental probes. Especially if you have a little LCD monitor, you can walk around and reveal spatial patterns of environmental variables (see this note: https://publiclab.org/notes/cfastie/05-26-2017/portable-thermal-ir-temperature-logger-unit). Ideally, a moving data logger would have a GPS sensor so each data point saved also has location data (see this note: https://publiclab.org/notes/cfastie/04-17-2017/skypod-endurance-test).

Many sensors are very inexpensive (<$10.00) and provide simple measurements (temperature, humidity, barometric pressure, brightness, noise level, movement, tilt angle, etc). Sometimes that is all you need, but often you have to adapt a simple sensor to tell you what you really want to know. For example, a tilt sensor in a float on a long arm can reveal changes in the level of the water the float is on. Or a noise sensor by a road can tell you how many cars drove past.

It sounds like you are interested in sensing water. Most sensors are not waterproof, so some engineering might be required to use them in or near water. A few sensors are designed for submersion (e.g., the DS18B20 temperature sensor). For long term deployment the data logger itself also has to be weatherproofed, so more engineering is called for.

DIY data logging has been a popular field for many years and there is endless information about it. One of the big challenges of doing it is that it involves a little bit of programming, electronics, engineering, data wrangling, and patience. It's a rare data logging exercise that does not push my limits in two or three of those areas, which is why I included the last item in the list. Arduinos are finicky little scoundrels, so be prepared.

So yes, lots of activities can be dreamed up to demonstrate data logging. What's your budget, time frame, and objective (and tolerance for setbacks)?


Carol chipped in on the mailing lists:

My first question is, similar to Chris's, what can the data loggers do? Conductivity? Turbidity? pH, dissolved oxygen? We could put different things in jars of water like known amounts of salt (e.g. make a calibration curve of salt concentration vs response, to make sure it's linear), and mix salt (inorganic) with food coloring (organic). Does the presence of food coloring affect the salt measurement, which might be applicable to complex environmental systems where there are inorganics and organics present? I'll keep thinking...

Responses from the mailing lists:

Hi Carol! So excited to work on this at Barnraising! Someone correct me if I'm wrong, but the data loggers will collect and store the data (also potentially transmit!) from whatever sensor we figure to add to it. So if, like we're talking about here, we're interested in temperature, we'll add a sensor for that.

Best, Stevie

@cfastie posted back::

That is correct, the loggers can have many different kinds of sensors connected to them. Several sensors can be connected at the same time. Most loggers do not come with any sensors by default, although many have a real time clock with a thermometer which can be read and reported. The Nano Logger Kit comes with a sensor for barometric pressure and temperature. The sketch loaded on the Nano will start reading that sensor, saving the data to SD card, and displaying it on the serial monitor. If you connect another sensor, the sketch will have to be modified.

The Mini Pearl Logger Kit does not come with a sensor, but the starter sketch for it (available here) will read time and temperature data from the real time clock, save it to SD card, and display it on the serial monitor.

Although these loggers can send data via USB to a computer and display it (serial monitor), transmitting the data elsewhere requires additional hardware (e.g., a radio for wifi or cellular).

Carol's list of parameters that sensors should sense (Conductivity? Turbidity? pH, dissolved oxygen?) includes some of the top picks for water quality monitoring. Unfortunately, inexpensive, off-the-shelf sensors can't sense those things. One could use inexpensive components to make a conductivity sensor or turbidity sensor, but that is a rather big project. One can buy sensors for those parameters, but they cost maybe $100 to $400 and might not work with some Arduino based sensors.

The realm of DIY data logging is a small subset of the realm of environmental sensing.

Carol's response:

Thanks, this is helpful. Coming from the environmental field in academia I have no idea what is available at low cost, and am looking forward to learning more and helping design studies for what is available.

So at the Barnraising, will we have different sensors to play with (and which ones)? Just temperature and time? I guess I'm still confused on how to help answer your original question, Stevie.

Best, Carol

Stevie's response:

Hi, Thanks again for clarifications and follow ups. Carol for the question I posted, was looking for activities to "get acquainted" with the data loggers. Especially for people who have a water interest. For example: "What type of activity could we test out doing at the Barnraising in an hour or so with the data logger (or loggers) we're bringing?"

I'm interested in exploring what that activity might be in hopes we could test it out and write it up so others can do it as a "first step to working with your data logger."

I think we'll have a few data loggers at the Barnraising, including some of the ones Chris mentioned, and one or two sensors - definately temperature. These clarifications and follow up questions are really helpful!


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