PICAXE GPS Locator Beacon - With Distance and Direction Calculation

This is the code that uses a 28X2 to read Latitude and Longtitude from a GPS module and transmits the absolute location of the module or its distance and direction as either fast 60WPM Morse or slow 15WPM Morse.

Based on low power true line of sight tests at 8.2km, at maximum output power (100mW) the line of sight range for decoding the Morse, using an UHF Amateur band reciever is in excess of 50kM for the auto decoded Morse (via the soundcard of a Laptop\Netbook), or if you can read the slow Morse by ear, the line of sight range should be 1000km or so..

The module has a distance calculation range of a little over 1 Degree Lat\Long in either direction, so approximatley 120kM in the UK.

The module can drive either a AXE133Y OLED\LCD display, showing current and home lat and long plus distance and direction, or can send the position data and a pile of debugging stuff, to an OPENLOG micro SD card logger, this data is output in CSV format.

The code runs over two slots, and there is an enhanced version of the GPS collector program which uses a timer or checks an model radio control pulse, to determine 'lost' status as a lost model locator, as soon as the code for that is checked out it will be posted also.

Many thanks to forum member Armp, who provide some of the routines use to persuade an integer only PICAXE to do some trigonometry. There is a bit of Mr Leach in there too.

The code could no doubt be improved upon, the short distance (under 1km) resolution could be better. In general the direction calculation is accurate to 1 degree.

And the code;

Brilliant! Just the ticket.

There is some furhter code to add, when I have the time, that will let the locator read the GPS and update its location in the background. Transmission of the location (or distance and direction) will then only be triggered when the locator decides its lost, either by failure of the read RC pulse or expiry of a failsafe timer.

Hi Srnet..

Very interested in your project as I also fly radio control aircraft but I am looking at it for possibly another purpose but not quite sure of the implications.

As a member of RNLI Lifeboat Crew, I've seen a few project on the forum that could be adapted to suit needs within our station. So far, I'm working on an 'Ops Normal' timer which is progressing at the moment but your GPS locator beacon brough a smile to my face in that I can see where it could prove very useful.

A month or two back, 'Fred' our resident practice dummy decided to make dummies out of us by deciding to go missing a few miles out to sea - all within the space of an hour. He was eventually found - 4 week later not far from where he was dropped off but had we had some mechanism such as your GPS locator built into 'Fred' but constantly pushing out GPS info, (No lost RC Pulse) we could have found him a lot quicker after he was misplaced.

In terms of the PCB board, do you have these available?

Many thanks

Declan

Your welcome to a couple of the PCBs, let me know and for the price of a couple of stamps you can have them. I had 10 made and have only used one.

There is a header on the PCB that will allow connection of a different or cable connected GPS module, sometimes the GPS need to be put in a location for best reception.

I also have some PCBs for this;

http://www.picaxeforum.co.uk/showthread.php?19549-RFM42-Lost-Model-Locator

Which allows 'things' to be found without the GPS.

Hi Srnet..

Many thanks for that. Very much appreciated. Can you PM your address and I'll send a pre-addressed envelope. The pcb's for the Lost model alarm would be appreciated.

Declan

Hi Srnet..

Sent you a PM regarding both pcb's

Declan

The GPS beacon PCB is larger than it might be, as it can be made with 1206 SMT components or wired components, the exception being the 28X2 SOIC which is mounted on the rear. There is a SMT MOSFET that is used to power down the GPS module, but if the GPS has a ENABLE pin its not required.

The 20X2 Locator uses SMT resistors capacitors and diodes, mainly 1206 size.

Development of this has not stopped. Performance of telemetry these devices are capable of was originally found to be adequate for normal purposes but of no use for a lost model application. Once I realised that I was using 868Mhz tuned RFM22s at 434Mhz and swapped to proper 434Mhz modules the reception distance improved dramatically and it now becomes feasible to use the RFM22 as a long range telemetry link from a model in flight.

Range tests carried out to date have shown a working LOS telemetry link of 8.2kM at 12mW. Recent checks on the modules antenna tuning indicate that distance is achievable at 6mW, possibly 3mW. The RFM22 is capable of 100mW.

Here is where I was carrying out the long range tests.

I am standing on Machen Mawr, my brother is on Caerphilly Common (picture centre) 8kM away.

If you want to know how far 100mW of FM Morse can get you, here is a short sample of a recording of a 100mW FM transmitter that was line of sight 2012kM away.

Receiver was a 70cm Yaesu tranceiver and a Arrow Antenna Yagi.

Its posted as a .pdf file, forum does not allow posting of .MP3 files, so download and rename it to an MP3 file.