Handsfree GPS director
I am looking at building a relativly 'hands free' GPS navigator for bush walking as a backup for magnetic compass work. Keeping track of distance and bearing in rough terrain can be very hard.
The concept is to take a known GPS position - "Here" and enter by thumbwheels/voice recognition/other method a distance and bearing and use the GPS as a backup for the magnetic compass. Basically if you are roughly on track then it is silent but should give an indication of when you have arrived. If going off course then a simple "bear left" / "bear right" audio prompt with an 'on course' finish. A count down of distance every 100m could also be provided. As hiking in the Australian bush requires carrying sufficient water, food and first aid gear as a minimum then I would like this to be small and light, hence the audio feed back and possibly data entry.
While I mainly use picaxe I realise this is NOT the right micro for this job. I have an Arduino Uno but am not comfortable in C. Another option may be the parallax Propellor I would like any feedback on microprocessor and GPS modules (406?) Text to speech looks like the TTS256 and speakjet but wav files on a SD card could be an option also.
UPDATE 15 Feb 2012 I have now completed the first proof of concept prototype. Simply put, on power up it waits until the GPS has lock. Prompts for user entry for the starting point (where they are currently), the distance (Km) and bearing to walk. The position is checked every 5 seconds (probably less often on the final), speeding up as you approach the target area. Once within 5m you have arrived. This process is then repeated until the user power offs. Prototype works well but has limitations. Main one is the size of the unit. I am now considering a graphical LCD as they are more compact than the 20x2 LCD I am using at the moment. This would also allow a better style of display when being used hand help. Another option I am also considering is instead of voice just three LED's, Red for Left, Green for Right and another colour for arrived. At the moment the code takes about half of the Arduino Uno memory space up. I am now awiating a SD card holder and some other goodies. I will probably have to switch to the Mega at this point to get sufficient digital pins
UPDATE 20 Feb 2012 I realised this weekend I had used the wrong formulae. The original formulae was for great circle navigation (shortest distance). However I neede rhumb line navigation (constant bearing), which is different. I have just about finished changing the formulea but also realise I am getting occaisional errors in the course (direction) error. This is partially due I feel to my short testing distances and the accuracy of GPS (+- 5m, WAAS is not available in Australia). Further testing will be done.