In field monitoring – storing the data on microSD


Today, when the storage cards price has decresed very much, reported to the quantity of data which could be saved on them, it is much easier to use such kind of devices in different kind of applications. One example is when we want to measure the parameters of the environment (temperature and humidity) without being necessary to view real time the measurements. We could left the device to realize its measurements for a period of time (a few days / weeks), and when the process is completed the data is analyzed and characteristic charts could be generated.

A very simple solution could be realized with the Seeeduino Stalker v2 board, using a micro architecture as presented in the figure below. It was defined as “micro” since the entire size of the device it’s just about 10cm. A corresponding firmware application have been developed for the main board. The RTC (Real Time Clock) module permits to know exactly the date & time of each measurement and should be initialized before starting the monitoring process.

The values form the sensor have been readed at every 10 seconds and stored into a log file (FAT16 format) on a microSD card (2Gb, enough space for let the device to work properly even for one year). The log file have designed to have a proper format for permiting a easily export of information to another formats. A model of the stored information is presented below (date & time, battery voltage, temperature, humidity and dew point values):

03/07/2011 07:52:53;413;2450;4199;1075
03/07/2011 07:53:03;413;2443;4215;1074
03/07/2011 07:53:14;413;2437;4231;1075
03/07/2011 07:53:25;413;2429;4247;1074
03/07/2011 07:53:35;413;2426;4260;1076
03/07/2011 07:53:46;413;2419;4279;1076
03/07/2011 07:53:56;413;2412;4288;1073
03/07/2011 07:54:07;413;2408;4301;1073
03/07/2011 07:54:18;413;2407;4308;1074
03/07/2011 07:54:28;413;2401;4317;1072
03/07/2011 07:54:39;413;2401;4327;1076

In our case the information have been exported into a Matlab application and used for generate charts with the parameters evolution. For this test the solar panel have not been used. Using it will increase even more the life time of the device.

Other sensors or actuators could be added to main board according to the specific of the application.

The next steps supposes to estblish some posibilities to optimize the energy consumption, permiting the device to function for as much time as possible.

  1. Edouard
    May 17, 2012 at 6:31 pm

    Could you post your code please ?
    I have a stalker v2.1 and get a value of 207 on analog pin 7 (lipo) but don’t understand how to convert it to mV.

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