A compass isn't just for the user to know which way they're facing; it's so that the GPS can tell you which way to turn before you set off in the wrong direction.

I'm just wondering if the accelerometer+GPS is good enough to fake a compass through dead reckoning. You turn on dead-reckoning mode, get a GPS fix, walk 20ft or so in a straight line holding the device in some predefined position and now the device knows what direction its facing. Or alternatively, you point the device north, tell it to sync, and it does.

Granted, last time I did anything with dead reckoning was a FIRST robotics competition 6 years ago and I remember that just failing horribly, but maybe things have gotten better since then?

1. Dead reckoning with a single accelerometer is trouble. You'd really need a gyro, accelerometers will give you onyl translation, but not rotation.

2. If you walked 20ft with GPS on, you'd have a direction anyway There is just one assumption to make - that the device was in front of you.

Or two accelerometers as far apart as possible in the phone. A magnetic bearing gyro sounds like it would give better results though. But then again, silicon accelerometer == no separate moving parts to fail.

You'd need to integrate the accelerometer measurements, which I'd think would have to be done continuously by the electronics to have a chance at being accurate.

i2c would be easiest to access using some microprocessor with a similar interface (Atmel has TWI or USI depending on model). I don't know if you can bit-bang the SDIO in the microSD, or if there would be a driver for the UART interface, though there is a NXP/Philips UART to I2C chip that might work.

I'd be really happy with an integrated bluetooth compass/headset. Or even just a BT compass.

It would mean that I'd have to keep the N900 aligned correctly, but I don't think holding the phone straight in front of me would be any kind of herculean task.

Looks like someone named "HapticGuide" is working on a bluetooth compass prototype for the N900:

http://www.flickr.com/photos/hapticguide/4206070945/
http://www.flickr.com/photos/hapticguide/4164852805/

AFAICT there is no user on t.m.o. with that username.

Anyone know more information about this project, or care to comment on the visible electronics in the photo?

EDIT: better photo added
EDIT: Found the project home page here; it's a PUSH project. Looks like it's intended for walking navigation, not for AR. I wonder if the compass circuit returns full 360 degree information or just 8 directions.

there is a strange blanking plate type thing inside the n900
go have a look at some disassembly videos, would a honeywell i2c unit fit in that space?

Shame this isn't available anymore:

http://www.wintec.com.tw/GPS/bluetoothgps/WBT100.htm
http://www.pocketgpsworld.com/wintec-data-logger.php

It actually spits out an NMEA HDG message, just what we could do with: http://www.gpspassion.com/forumsen/t...88&whichpage=5

That Wintec device does indeed look like it would fit the bill surprisingly nicely: small, battery-powered, and bluetooth! Looks like it was pricey when it was available ($150)... wonder if there's a similar product available today.

EDIT: Is this the successor? Seems like it's still available. Looks like you'd be paying for a lot of stuff you don't need though if all you need is a compass.

I seem to recall someone in this thread said (s)he had contacts to a Chinese manufacturer who might be willing to take up a compass project. I wonder if the Wintec might be able to serve as a useful example for said manufacturer when considering development of a similar device.