Data logger – Step 2 – Equipment

In this second article, I will describe the material that I use at the moment and how it is configured


Here is the list of components that I currently have on my recorder :

  • Two push buttons. The first allows to start or stop the recording of data. The second by long press to switch off the system.
  • A green LED to indicate that the system is ready to begin a recording
  • A red LED to indicate that recording is in progress
  • A clock RTC DS1307 to have the correct time when the system is not connected to the Internet
  • A gyroscope/accelerometer MPU6050 to measure the slope on 3 axes of the data logger
  • A GPS. I made the choice to a USB GPS like the one I presented here. The cost is the same that a card and especially the GPS can be deported from the recorder which allows to fix elsewhere if necessary.
  • A probe DS18B20 to record the temperature. I took this model (compared with the DHT22 probes for example) because it may as the GPS be output from the recorder through a long enough cable and it is waterproof
  • Resistance between 4.7KΩ and 10KΩ for the connection of the probe on the Raspberry
  • A housing 6 AA batteries
  • A voltage regulator LM2596 to regulate the voltage from the batteries
  • A breadboard
  • Wires

Apart from the GPS to 37$, all the components are little expensive and coping well with ebay or shall be limited to the invoice unless 50$ or 60$ (without the Raspberry).

The connection here is the diagram of the recorder :


Attention, Fritzing is not all components in the list so I took to the nearest on gyro (not MPU6050). There is also a “Tip” concerning this gyro. I added a cable between Vcc and the Add entry to change your address on the i2c bus (0x 68 instead of 0 x 69) If not there is a conflict with the address of the clock.

Same thing for the DC - DC Step down. I put wires but if you have a LM2596, you have all the information to plug into this article.

It now remains to configure Pi Raspberry for his new friends !

To the 19/03/2014, There is a bug in the Raspbian that prevents the simultaneous use of the i2c bus and the 1-wire bus. To use an older version which you can download here.

  1. Download and install Raspbian. Take the version of 25 September 2013
  2. Update the system but without any upgrade
     apt-get update
  3. Disable the modules in the file /etc/modprobe.d/raspi-blacklist.conf. Here are the contents of the file :
    # blacklist spi and i2c by default (many users don't need them)
    blacklist spi-bcm2708 #blacklist i2c-bcm2708
  4. Enable the necessary modules. Here are the contents of the file /etc/modules :
    # /etc/modules: kernel modules to load at boot time.
    # This file contains the names of kernel modules that should be loaded
    # at boot time, one per line. Lines beginning with "#" are ignored.
    # Parameters can be specified after the module name.
    SND-bcm2835 i2c-bcm2708 i2c - dev rtc_ds1307 w1-gpio w1-therm

    Here is the list of the modules in memory after a reboot

  5. Restart the system
  6. Install tools for the i2c bus
    apt-get install i2c-tools

    You can check that your clock is well detected by position 68 and the accelerometer in the position 69 :
    1__sshThe 50 comes from the second possible port of my clock.

  7. Install and configure the clock (Replace it 0 by 1 If you have a model B revision 2)
    echo ds1307 0x68 > /sys/class/i2c-adapter/i2c-0/new_device hwclock r

    1__sshAs you are connected to the Internet, your system must be on time. Send time system to clock

    hwclock -w

    The command returns no information. You can check the result with the read command

    hwclock -r

    To sync automatically with the Raspberry boot, You must edit the file/etc/rc.local by adding the following lines before the exit 0 the end

    echo ds1307 0x68 > /sys/class/i2c-adapter/i2c-0/new_device sudo hwclock s


  8. Install the tools for GPS
    apt - get install –y gpsd gpsd-clients

    You can test that the GPS is connected

    cgps s


    Edit the file /lib/udev/GPSD.hotplug by adding the line

    chmod a   rw $DEVNAME

    before the line

    gpsdctl $ACTION $DEVNAME
  9. Test the Sensor DS18B20. In the directory /sys/bus/w1/devices, You must find your probe in the form of a directory whose name begins with 28-. In this directory you will have a file containing the measured temperature. It will be updated every time you go to read the contents of the file. Here is a complete example for the temperature :
  10. Test the accelerometer MPU6050
    i2cget y 0 0x 69 0 x 75

    The command should display 0 x 68

Your hardware is now ready ! Next step, use Python to save data

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