Newbie needs directions for GPS project

GPS/GNSS Development Boards
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I want to make a GPS device (the simplest one possible) that will receive GPS data, compute them and then output result as a simple signal (audio signal with piezzo buzzer or visual signal with several LEDs). The result would be something like current speed (or how close it is to pre-programed target speed; one, two or all 3 axes), current heading, etc.

So I was thinking of combining GPS module, some sort of processor (simple calculation and output) and an output for buzzer and diodes. I have no idea how to choose GPS module and what processor to use, so any help there will be highly appreciated.

If possible the entire package should be small and light, it will be used in clear air (up in air on top of skydiving helmet), it should do well with altitude (accuracy wise; barometric altitude sensor could be added to correct the data but first I want to have working proof of concept), faster sampling rate is preferable (5Hz or more). Absolute position on the globe is not most important, what is important is relative accuracy between measurements (I don’t care if position is 50m off if all locations are 50m off in the same direction). Good signal “retention” (planes are metal tubes and GPS inside a metal tube is… well bad) would be great. Battery requirements are not very strict, basically anything over few hours will be fine, but longer is better. I would also like to have capability to download GPS data to a PC, but that can be added after having working device. It should be dumb-proof device; one button to turn on, device does its job, same button to turn off. Pre-programed (via PC) to do the job.

Is this doable or am I asking for too much? If doable, which component would you suggest to build the device? Any other advice (or links or literature reference) is appreciated.

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antonija:
I want to make a GPS device (the simplest one possible) that will receive GPS data, compute them and then output result as a simple signal (audio signal with piezzo buzzer or visual signal with several LEDs). The result would be something like current speed (or how close it is to pre-programed target speed; one, two or all 3 axes), current heading, etc. […]

Sure it is doable.

Since you are initially targeting a proof-of-concept, I’d choose components based on comfort and reliability.

Having had positive experiences with the ublox modules, the sparkfun GPS-09566 would be my preference.

Also, it comes with an omnidirectional antenna already integrated, which saves a lot of hassle.

Get the GPS-09123 interface cable, too. The EM-406A would also be ok, except it has a 1Hz max position output rate.

Next I’d budget the power requirements. I’m wild guessing 150mA (50mA for GPS, 15mA for the CPU, the rest

for buzzer and/or LEDs). A (cellphone-type) 700mAh Li-ion would last for 4-5 hours. Rechargeable makes sense since you want to connect to a PC via USB anyway).

Next is the microcontroller.

Wild guessing again I’d budget 14KB for code including USB, 2KB for RAM, 1-2 UARTs and other stuff.

For logging and downloading GPS data to PC, you need a serial flash memory (or an SD card) interfaced via eg SPI from the microcontroller. The flash file system will need another 4-6KB of code.

Choice should be guided by these requirements, plus the availability of development/prototyping boards.

My personal choice would be a Silicon Labs C8051F34x which has all that is needed including USB, two Uarts etc.

But a GPS-08785 ArduPilot (Atmega328) would also be an attractive option if only because you can

get started right away and there’s lots of help available on forums. Alas, no USB, only one UART. BTW the 2nd UART is meant for debugging the firmware.

Other items are power supply and charging circuit.

For the firmware, sketch an architecture (tasks etc.).

The calculations from GPS NMEA speed to buzzer or LEDs are a bit involved:

that’s why for starters and through much of development you can use the VTG message which gives you heading and speed over ground (not a 3D-speed!). At some later point you just plug in the real 3D velocity.

Hope this helps,

E

PS: if you are only interested in heading and airspeed, why not use an airspeed sensor and a compass?

Oh I forgot, you want that helmet-mounted. Never mind.