Published June 13, 2019 © GPL3+

Cellular SOS Button Tracker

A device similar to a medical alert button that can be use anywhere where cellular service is available.

IntermediateFull instructions provided10 hours1,684

Things used in this project

Hardware components

Raspberry Pi Zero Wireless

GPS receiver (generic)

Huawei 3G USB Dongle

SORACOM Air Global IoT SIM

Software apps and online services

Raspberry Pi Raspbian

Story

My idea for this project is to create a device similar to a medical alert button. This device can be used anywhere there is cellular service. The way I built this is more like a tracker, but to add an actual button would be a minor change.

The way it works is once it powered up, there is a cron job that will run a getdata.sh script every 5 mins. This script will call a GPS python script The GPS script will then get the coords, convert it to latitude and longitude in degrees, and out put the values in JSON format. The getdata.sh will then take that JSON output and upload it to Soracom Harvest where it will store the data.

Here is a sample of the JSON output

{ 'latitude' : 48.1173 , 'longitude': 11.5167  }

And here is what it looks like in Soracom dashboard

I had an issue retrieving the data from Soracom's Harvest. I tried a few different ways and still not able to get it. As you can see above, the data is there and can be viewed using Soracom's Data viewer.

The Build

For the build, I'm not going to explain all the steps as there are other tutorials that will do a better job than I can so I will reference them instead.

Set Up the Raspberry Pi

Download the Raspbian image to your PC.
Follow these instructions to install Raspbian.
Connect everything to the Pi, I connected a keyboard, mouse and monitor as it makes this job easier.
Insert the SD card into the Pi.
Power it up and finish the install.

The easiest way to do this is to follow these instruction. This will explain how to setup the dongle and how to make the necessary changes to the Pi to allow it to pickup the dongle every time its rebooted.

Connect the GPS Sensor

I used this image to make the necessary connection to my Raspberry Pi Zero. The image is taken from lokesh chandak site. It shows a Raspberry Pi 3, but the connections and instruction are the same.

From lokesh chandak GPS build

Set Up Soracom's Harvest

I used these instruction to setup Harvest on Soracom. If you have your USB modem dongle set up correctly, after you set up Harvest, you should be able to run some of the examples at the bottom of the instructions.

Load the Software

At this point you should have a working Pi with the GPS connected. Now we need to load my software.

Power up the Pi and log in. (I log in as Pi and use my home directory/home/Pi).
Create a directory called GPS.
Copy the the gps.py and getdata.sh to the /home/pi/gps directory ( make sure you have execute permission on the getdata.sh script.
At this point you shouldn't need to change code. You should be able to run the getdata.sh and it should upload the GPS coords.
If all works correctly, you can add the cron job to the crontab. the command is crontab -e then you just have to cut and paste the line listed in the cron job code section.

Issues

I said it above, and one of the biggest issues was retrieving the data. I can do it using Soracom's data viewer, so I know the data is there. I tried a few different ways like sending a GET command using curl, but it wouldn't return my data. I also found another site on the developers soracom site, but I still couldn't get the data back. Not sure what is wrong at this point.
Second issue is using a Raspberry Pi. The problem is there is no power management on a Pi. So this build really isn't practical unless you are using it connected to a good power source.

Conclusion

I would like to thank Soracom and Hackster for giving me the opportunity to build this project. I had a few issues with it, but in the end I was able to build a device that would update the location of the user. Even though I think it isn't practical to carry on a person because of the power requirements, it could be used on a vehicle or motor bike where it can be wired to a battery that is constantly getting charged.

Thanks,

Dana

Code

import serial               #import serial pacakge
from time import sleep
import webbrowser           #import package for opening link in browser
import sys                  #import system package

def GPS_Info():
    global NMEA_buff
    global lat_in_degrees
    global long_in_degrees
    nmea_time = []
    nmea_latitude = []
    nmea_longitude = []
    nmea_time = NMEA_buff[0]                    #extract time from GPGGA string
    nmea_latitude = NMEA_buff[1]                #extract latitude from GPGGA string
    nmea_longitude = NMEA_buff[3]               #extract longitude from GPGGA string

    lat = float(nmea_latitude)                  #convert string into float for calculation
    longi = float(nmea_longitude)               #convertr string into float for calculation

    lat_in_degrees = convert_to_degrees(lat)    #get latitude in degree decimal format
    long_in_degrees = convert_to_degrees(longi) #get longitude in degree decimal format

#convert raw NMEA string into degree decimal format
def convert_to_degrees(raw_value):
    decimal_value = raw_value/100.00
    degrees = int(decimal_value)
    mm_mmmm = (decimal_value - int(decimal_value))/0.6
    position = degrees + mm_mmmm
    position = "%.4f" %(position)
    return position

gpgga_info = "GPGGA"
ser = serial.Serial ("/dev/ttyS0")              #Open port with baud rate
GPGGA_data_available = 0
GPGGA_buffer = 0
NMEA_buff = 0
lat_in_degrees = 0
long_in_degrees = 0

try:
        while GPGGA_data_available < 1:
                received_data = (str)(ser.readline())                   #read NMEA string received
                # Sample data below was used because GPS sensor wouldn't work inside.
                #received_data = "$GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,545.4,M,46.9,M,,*47"
                print("in while loop")
                GPGGA_data_available = received_data.find(gpgga_info)   #check for NMEA GPGGA string

        GPGGA_buffer = received_data.split("$GPGGA,",1)[1]  #store data coming after "$GPGGA," string
        NMEA_buff = (GPGGA_buffer.split(','))               #store comma separated data in buffer
        GPS_Info()                                          #get time, latitude, longitude

        print "{ 'latitude' :", lat_in_degrees, ", 'longitude':", long_in_degrees, " }"


except KeyboardInterrupt:
    webbrowser.open(map_link)        #open current position information in google map
    sys.exit(0)

Credits

Dana Mah

12 projects • 27 followers

I'm a hobbyist interested in microcontroller solutions to simple problems.

Thanks to lokesh chandak .

Cellular SOS Button Tracker

Things used in this project

Hardware components

Software apps and online services

Story

The Build

Issues

Conclusion

Schematics

GPS sensor to Pi

Code

gps.py

cron job

getdata.sh

Credits

Dana Mah

Comments

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Cellular SOS Button Tracker

Cellular SOS Button Tracker

Things used in this project

Hardware components

Software apps and online services

Story

The Build

Issues

Conclusion

Schematics

GPS sensor to Pi

Code

gps.py

cron job

getdata.sh

Credits

Dana Mah

Comments

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