Category Archives: DIY Cell Phone

DIY Cell Phone

GSM Phone Tracking Methods

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I decided to conduct a few tests with my fona808.

  • Battery. The at+cbc command give you the current charge mode, percent charged, and millivolts. I found on the adafruit fona808 that the charge mode indicator always gave status 0 (“not charging”) even when charged.
  • GSM Location. This is given by the at+cipgsmloc. It spits out lat and lon. I don’t know where it is getting the data from, but based on the plots I made the location it gives is an estimate based on your location to the nearest cell tower.
  • GPS. Given by at+cgnsinf. I found this to be spot-on, always accurate, even with my pea-sized GPS antenna!
  • DIY cell tower triangulation. If you put the fona into ENG mode (“AT+CENG=3”), it will give you the MNC, MCC, LAC, and CellId for the towers around you (i usually got six reports per “AT+CENG?” query). You can then use a site like cellphonetrackers.org to turn the tower info into a lat/lon coordinate. The +CENG messages also given a power level which you can use, in cojunction with the cell tower lat/lon coordinates, to perform the triangulation. The method of doing this is described elsewhere, but basically each power level becomes a weight, w_i = rx_i / (rx_0+rx_1…rx_n), which is multiplied by the lat/lon of the corresponding cell tower item. You then just add up the weighted lat/lons, and viola!

      • My results?

      • I found that i lost about 10% power on my 1 hour trip. This seems terrible – barely 10 hours per charge, extrapolating.
      • The GPS info was perfect. It took about 2 min to acquire
      • The GSM location was too course, but was actually more clean than my DIY location
      • DIY location seems crumby. Im not sure what would fix this. Possible things to look at: 1) Filtering. Maybe I could throw out the lowest power rating, or smooth out the locations somehow. 2) See if there are better cell tower dbs. As far as i know, cell tower info isnt public, so any db is most likely based on reported, possibly inaccurate, values

      Here’s a map with plots of the three localization methods: GPS (magenta), GSM (green), and DIY Triangulation (yellow).

      gsmtrack

DIY Cell Phone

My favorite FONA commands

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These are more like “the commands i have found useful as of present.” I bear no real affinity for them, except that I do appreciate the data they yield.

AT+COPS? Ensure you are connected to the network (it gives “+COPS: 0” if you are not)
at+ccid Get the SIM number; you need this for activation
AT+CMGF=1 This sets us into text mode. I haven’t used the other mode (PDU) yet.
at+sapbr=3,1,”contype”,”gprs” You can set the connection type to GPRS (data) or CSD (circuit switched) – i think this is why you can call or do data on gsm networks, but not both (at the same time).
at+sapbr=3,1,”apn”,”wholesale” Until you set your access point name, you might not be able to do things like geolocate (based on cell towers) or do data stuff. TING’s APN is “wholesale” – im sure it is different for every provider.
at+sapbr=1,1 Open up your bearer. . . sounds good, but im not entirely sure what that means.
at+cipgsmloc=1,1 This gives you your lat/lon. Note that on my old T-Mobile sim card, which had no data plan, i got nothing back for some reason; apparently you have to have a data plan to get this info?

For SMS (which i used only briefly) I found the following useful:

at+cmgl=”all” I didn’t realize this, but all text messages really are stored somewhere in the providers network, at least until you do something with them (makes sense) – i just found it interesting that I transplated my SIM card from my tmobile device to my FONA, and could see text messages from years ago.
at+cmgs=”180188xyzwl” This is of course how you send a text. You press enter, after typing the phone number (“1801..” – notice the leading “1”, since im in the USA; not sure if this is needed, but it works with it). When you are done you must hit ; if you hit it cancels the message!
at+cmgr= This is your way of reading a text message

For GPS I used the following (note I have v2 of the FONA808 – the commands are different for v1)

AT+CGNSPWR=1 The device starts with the GPS off. So i turn it on, cause i want it.
AT+CGNSINF Gives you a crudload of gps-related info, including lat-lon, altitude, utc, etc. (see table 2-2 in the “SIM800 GNSS Application Note”)
DIY Cell Phone

DIY Phone

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I was recently granted an adafruit shopping spree by my wife. I chose a FONA808 and some Trinket microcontrollers (literally they are about the size of my thumbnail!).

Im still learning the ins and outs of the FONA, but it is amazing how much momentum you can gain by simply following the instructions listed in the adafruit tutorial. Since I spent a couple hours due to my failure to read I thought I would pass on for some other soul, like myself, the importance of simply doing what lady ada says. Namely: 1) DO connect your power source (battery, usb +5, whatever) to VIO, and 2) if you don’t see the blue light shining hold down the little button on the module for two seconds (or just tie KEY to ground). These two things will work wonders.

Oh, and for those using OS X, I found much success by using the USB serial cable available on adafruit. I just downloaded the drivers from the product page, downloaded coolterm, and away i went. The autobaud on the fona works marvellously, as witnessed by it echoing back after I typed “at” a few times.