How to Build the Open GPS Tracker

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How to build the Open GPS Tracker

PC boards, kits, and assembled units are for sale here!

The tracker is easy to build on a perfboard. I used a basic one-pad-per-hole perfboard and 26-gauge wire, but30-gauge would probably be better. All the electronic parts are available from Mouser Electronics. Radio Shacksells the perfboard and the 2.5mm plug for the phone. You could also buy these from Mouser.

If you are building a tracker, please post in the user forum. I am looking for bug reports, pictures, andinformation about how the tracker works for you. I will provide technical support to people who are buildingunits.

Click here for information about using the Aarlogic GPS 3A GPS module and Telit GC864 GSM module.

Caution: I have seen two units with the power transistor installed backward. If you reverse the emitter andcollector, the transistor will conduct weakly. The power light comes on, but the device either returns NODATASTREAM or never replies. With the regulator and transistor installed side by side, and the output of theregulator next to the emitter of the transistor, the flat sides of the two components face in opposite directions. Ifthey are facing the same way, the circuit will not work!

The Mouser Electronics (http://www.mouser.com) order is listed below. This order includes an AVRISP2, whichyou may not need if you already have an AVR programmer. I've included two each of all the small parts, andthree of the GPS module connectors. This connector is the only tricky part of the build. It is easy to ruin one, as Idid. For testing, you can just insert the 26-gauge wire into the socket on the GPS module, but for permanentassembly you need the connector. The connector has one extra pair of pins, which you should cut off. You will besoldering to the long side and plugging the short side into the GPS unit.

You need to solder to four pins on the GPS header, three of which are right next to each other. Clamp the headerwith a small vice or a "third hand" clip. Bend the wire into a loop with pliers and attach it to the pin, thencarefully solder it. I solder pin 3 and pins 7 and 11 first, putting the wires down low near the plastic separator,then solder pin 9 with the wire up high away from pins 7 and 11. Check for shorts with a meter.

I superglued the IC socket and the two rows of three pins for the programming port, then wired those togetherand installed the rest of the components. Put the 0.1uF capacitor right next to the IC socket. The GPS module isattached to the board with 2-32 size screws, nuts, lock washers, and 1/4 inch spacers, which are not quite longenough. Get 3/8 inch spacers if you mount it this way.

Mouser Part # Description Quantity Price Each

556-ATTINY84-20PU Atmel AVR microcontroller 2 $2.90

827-AME8811AEATZ 3.3 volt regulator 2 $0.69

How to build the Open GPS Tracker http://www.opengpstracker.org/build.html

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522-ZTX1151A PNP transistor with low saturation voltage 2 $1.51

581-SA105E104M 0.1 uF ceramic capacitor 10 $0.08

581-TAP106K006SCS 10 uF tantalum capacitor 4 $0.50

855-M50-3501242 1.27mm M50 connector for GPS device 3 $1.45

171-0025-EX 2.5mm stereo plug for phone 2 $1.35

571-1-390261-3 or571-26415994

14 pin IC socket 2 $0.15

604-WP937EGW Two-color red/gren LED 2 $0.34

604-WP132XID Red LED 2 $0.12

660MF1/4DC3321F Resistor 3.32K ohm 5 $0.03

660MF1/4DC4700F Resistor 470 ohm 5 $0.03

755-1N4148T-77 Switching diode 5 $0.03

12BH431-GR 3 AAA battery holder 1 $0.89

571-41032390 Pin header 40-pin breakaway 1 $1.57

340-V23993-A1035D Vincotech GPS receiver module 1 $61.50

556-ATAVRISP2 AVRISP2 USB AVR programmer 1 $35.91

Drawings below donated by Empowered Web Development

Microcontroller schematic


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Power supply schematic for 4.5V battery


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Programming plug


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GPS module socket, module facing antenna down

Checkout process

When you finish building the project, perform these checks. This will prevent destruction of components andverify that the circuit is built correctly.Unpowered checks with no batteries, MCU, phone, or GPS installed:

Check continuity from the negative battery terminal to MCU pin 14, phone jack ground, regulator centerpin, and GPS header pin 9.Check continuity from the positive battery terminal to the input pin of the regulator.Check continuity from MCU pin 1 to the output of the regulator.Check for shorts between all adjacent pins of the MCU, programming header, phone jack, and GPSmodule. There should be no continuity between any adjacent pins.Check continuity from each pin of the programming header to the corresponding MCU pin.Check continuity from each pin of the phone jack to the corresponding MCU pin.Check continuity from pin 3 of the GPS header to pin 11 of the MCU.Place the GPS header over the GPS module and make sure you have wired the right pins.The plug is very small and mistakes here are expensive. All the wires should be on the inside row of pins,closer to the metal shield. No wires should be on the outside row closer to the edge of the GPS module.

Powered checks with batteries but no MCU, phone, or GPS installed:

Measure voltage between pin 1 and pin 14 of the MCU socket. You should have 3.3V with pin 1 positive.Measure voltage between pins 9 and 11 of the GPS header. You should have close to 3 volts with pin 11positive.Place a jumper between pins 5 and 14 on the MCU socket. The red "GPS active" LED should light.With the jumper in place, measure voltage between pins 7 and 9 of the GPS header. You should have 3.3Vwith pin 7 positive.Remove the jumper, and place it between pins 1 and 2 of the MCU socket.Place another jumper between pins 3 and 14 of the MCU socket. The two-color status LED should lightred.If it lights green, it is installed backward and all status codes will be reversed in color.


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Reading status codesThe two-color status LED blinks to provide status codes. Status codes are two-digit numbers which assist indebugging. The first digit is always shown in green, and the second digit in red. For example, one green blinkfollowed by three red blinks is code 13. Three green blinks followed by two red blinks is code 32. The statuscodes are displayed one at a time from a queue, so the event that caused a status code may be over by the timethe code is displayed.

Code Description

11 phone polled

12 send message failed

13 phone poll failed

14 no phone number defined

21 invalid password

31 power on or reset

32 watchdog reset

33 eeprom initialized from defaults

34 remove jumper to reinit

Final checkout and setup

Remove one battery, install the Atmel MCU, and put the battery back in.If your MCU is unprogrammed, connect the AVRISP2 to the computer and to the board via theprogramming header. Both lights in the AVRISP2 should be green.Download the appropriate HEX file for the units (feet, meters, MPH, KPH) you want from the Downloadlink at the top of this page.Run AVR Studio. Choose Tools, Program AVR..., Connect.Choose AVRISP mkII and USB. Click Connect.Some AVRISP2s need an upgrade to work properly: http://www.atmel.com/dyn/resources/prod_documents/avrisp_mkii_fix.htmlChoose Board tab and set ISP Freq to 125 kHz. Go back to Program tab.Device should be ATtiny84. Programming mode is ISP. Erase and Verify boxes checked.In Flash, Input Hex File, choose your Hex file. Click Program.The programming status window should show OK.The status LED will begin blinking shortly after the programming completes. With no phone attached, youshould get codes 31 (power on or reset), 11 (polling phone), and 13 (phone poll failed.) A freshlyprogrammed chip will also display code 33 (EEPROM initialized) once.Charge the Motorola C168i mobile phone. Install the SIM card and activate the prepaid service using theinstructions included. Call the interactive voice response system at 1-800-901-9878 and activate amessaging plan (200 messages for $5.00, keywords: buy features, messaging, 200, yes, buy it) to avoidbeing charged 15 cents per message. You should be able to send and receive SMS messages from the phonekeypad.Configure the phone for short (10 second) display backlight (Settings, Initial Setup, Backlight, 10 seconds.)Set the phone to silent mode (Settings, Ring Styles, Style, Silent.)Set message delivery to Phone first (Message, Options, Memory Meter, Select SMS Memory, Phone First.)If you do not do this, Powersave mode will not work!Remove a battery from the tracker's battery pack. Connect the Vincotech GPS unit to the header, checkingagainst the diagram to make sure it is plugged in correctly.Install the removed GPS battery, and then plug the 2.5mm plug into the mobile phone's headphone jack.The headphone jack is also the data port on this phone.You should get code 11 (polling phone) but no code 13 (poll failed.) If so, your microcontroller iscommunicating with the phone.If you get code 13, reset the microcontroller by momentarily shorting pins 5 and 6 on the programmingheader. If you still get code 13, unplug the phone and power cycle it.


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Removing the GPS battery with the phone connected is not recommended, and will not reset themicrocontroller. The phone will partially power the microcontroller through the output line and aprotection diode in the chip.When you get code 11, and no code 13, your unit is ready for setup.Please post to the user forum. I want to hear about working trackers, and will provide support for anyonehaving trouble with one.

Setting the reply addressThe GPS tracker stores a reply address, and always sends messages to the reply address. It does not care wherethe messages come from, because messages sent from email do not include the From address (using AT&TGoPhone service.) The reply address can be a mobile phone number or an email address. Regardless of wherecommands are sent from, replies go to the reply address.

To set the reply address to a mobile phone number, use a mobile phone to send a text message to the tracker'sphone number:GPS SETADDRESS 8185551212where 8185551212 is the mobile number you want tracker messages sent to. The "GPS" must be uppercase. TheSETADDRESS can be upper or lower case. After sending the message, the tracker's phone display should light,the tracker status light should blink code 11, and you should receive a reply saying "COMMAND EXECUTED".

To set the reply address to an email account, you need your carrier's Email Gateway number, which is a specialphone number used to route text messages to an email account. For AT&T the Email Gateway number is 121. Forother carriers, go into the phone's SMS settings (Messages, Options, Message Setup, Text Messages, EmailGateway) and look up the Email Gateway number. Send a text message to the tracker:GPS SETADDRESS 121 [email protected] "GPS" is in uppercase, 121 is the Email Gateway, and [email protected] is the email address. For AT&Tservice, you can send an email to [email protected] ([email protected]) to send a text message.For other carriers, you will have to look up the correct email address. The tracker will reply "COMMANDEXECUTED."

Requesting a locateOnce you have set your reply address, you can request a locate. Send the message:GPS LOCATEwhere GPS is in uppercase. The tracker's phone display will light, the status LED should blink code 11, and theGPS power LED should come on. For the first locate, it will usually stay on for a minute or more. When the GPSlight goes out, the status LED will blink code 11 again, and you should receive a reply:LOCATE POS 34 05.8779 N 118 20.6368 W ALT 377 FT SPEED 0.0 MPH COURSE 11.05 AT 08/04/05 22:31:51UTC SATS 04This is a location report from the tracker. The fields are:

LOCATE - the report is the result of a manual locate request. There are other types of reports in trackingmode.POS 34 05.8779 N 118 20.6368 W - latitude and longitude in degrees and decimal minutes. You cantype or paste everything after POS right into Google Maps (http://maps.google.com) to see a map orsatellite view of the location.ALT 377 FT - measured GPS altitude, only accurate for 4 or more satellites (see below)SPEED 0.0 MPH - speed of the GPS unit when the fix was taken. A unit sitting still often reports up to 2mph.COURSE 11.05 - course in degrees if the unit was movingAT 08/04/05 22:31:51 UTC Year, month, day, hour, minute, second Universal Coordinated Time thatthe fix was takenSATS 04 - number of satellites providing the fix. Four or more indicates a 3D fix (altitude valid) whilethree satellites indicates a less-accurate 2D fix.

If you get a valid location report, your tracker works. If you get "GPS TIMED OUT WAITING FOR FIX" thetracker is not in GPS coverage. Although the A1035 gets a fix inside most buildings, steel construction can blockthe signal. Take the device outside and try again.


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If you get "NO DATASTREAM FROM GPS DEVICE" your GPS module is not sending any data to themicrocontroller. Check for faulty connections and verify that power is applied to the GPS module when the GPSpower LED is lit. Dead GPS batteries can also cause this error, since the microcontroller needs less power thanthe GPS module.

Securing your trackerThe "GPS" prefix you have been putting before commands is actually a default password. You can and shouldchange it. Anyone who knows your password can change it and take control of the tracker. Unlike commands,the password is case sensitive. To change it, send a text message like:GPS SETPASSWORD newpass newpassWhere "newpass" is the new password you want to set. It must be between three and sixteen characters, andmust be repeated twice after SETPASSWORD. You should get back "PASSWORD CHANGED." You would thenhave to send "newpass LOCATE" to request a locate, for example. If you lose your password, you need physicalaccess to the tracker to clear the configuration (see the command reference.) Messages sent without the correctpassword will be ignored.

Other things the tracker can doSo far you have seen the normal mode, in which the tracker replies immediately to requests. The tracker has twoother modes: tracking and powersave.

In tracking mode, the tracker automatically takes GPS fixes, and sends you a message when it starts moving,when it stops moving, when it goes out of GPS coverage, and periodically while it is moving. You can plot thefixes on Google Maps or a similar service to follow the tracker's movements. You can configure how often thetracker takes a fix and how often it alerts you. You can also set a speed limit and receive an alert if it is exceeded.

In powersave mode, the tracker turns the phone power on and off periodically, allowing the phone battery tolast longer than its typical standby time. For example, the phone may be off for an hour and on for ten minutes.In this case, it can take up to an hour for the tracker to reply to messages. You can remotely take the tracker outof powersave mode when you need location reports. Tracking and powersave modes are mutually exclusive;setting one mode clears the other.

The tracker has several configurable options, and a status command that reports the current settings, the phonebattery status, the phone signal strength, and the firmware revision. You can set a name which will be prefixedto all tracker replies, so several trackers can report to the same destination. See the command reference fordetails.


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How to Build the Open GPS Tracker

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