I've found on ebay a compass for arduino mini pro.
(about 20$)

I've also bought an arduino minipro 3.3v (about 20$)

I've bought a bluetooth module for arduino (about 40$)

Do you think that it is possible to construct a bluetooth digital compass with this?

I was very surprised that Nokia itself was implicated in a project for arduino on n900 with bluetooth.

There is even a python script for arduino on n900.


You will tell me, that 80$ is very much for a poor person.

But I always wanted to make experiments with arduino. Now I've got the script, the instructions of Nokia and the motivation (digital compass).
I never thought that arduino worked so well with n900.

Do you think there is any hope for success?

Yes ofcoutse, it should be straight forward

Apologies for the very short reply above, I was texting it from the bus on the way home from work last night. Yep the good news is that this project is very do-able Ive made a few arduino projects communicating to the N900 over Bluetooth, although not using a minipro board. As long as it has (and it should have) the correct pins for the Bluetooth module (TX, RX,..) you'll be golden.

Speaking of which, what type of module did you buy? I use a BlueSMiRF and it's pretty well straightforward. Depending on your experience of soldering, the only tricky bit to setting it up is soldering in 6 pins so you can connect it to the breadboard/or your own socket etc. When it arrives it wont have a connector, but you'll see 6 holes at the bottom of the module where these pins should be soldered. What i did was take a row of male-male header pins, snip off a row of 6 so they're still connected to each other, bent them at right angles, and soldered the pins on one side to the 6 pin hole contacts of the module. Bending at right angles means I can push the other side of the pins directly into the breadboard while keeping the module vertically upright.

The second trick to BlueSMiRF is pairing the module to the N900. You probably wont get the shared password/pin with it, so to save you searching around it is "default". You connect via the N900, search for bluetooth connections, pick the BlueSMiRF, and "default" will be your security pin. You'll see the red led on the module turn to green when connected.

You already have python sketches for reading/writing and there'll be Arduino examples all over the net. You should be able to find what you need there.

The only other type I can think of might save you hours of frustration If your arduino is running a previous bluetooth sketch and you want to upload a new one, you may find that it will fail to upload - probably because the BlueSMiRF module is busy doing it's thing. The trick is to remove the power to it so the module isnt running then upload the sketch and reattach the power.

I'll be interested to know how your project goes, keep us updated

Thank you, for your very competent advices.

Bluesmirf was also my preferred bluetooth module, because it appeared in a tutorial for arduino with n900.

But it was to expensive to me.

So I've bought this one:
http://cgi.ebay.com/Arduino-Serial-P...item2563f92b8a

It seems to have the pins already fixed. I don't know if the pins are compatible.

Do you think it could work?

(The digital compass has an explicite instruction for arduino mini pro 3,3v)

hmm havent seen that module before but im sure you can make it work. Looks like there are more pins than on the BlueSMiRF but i cant zoom in on my phone to read them clearly. Anyhow it should work, and if it arrives with the pins already soldered in that'll save some time too

Have you had much experience working with arduino projects/electronics projects in general? Not to be concerned if you haven't, it's a great hobbyist platform and all skills can work with it. Just interested to know if you have other projects, Im always interested in finding out what people have made with it

When I was very young I was very interested in electronics. But I didn't understand much.

I did even some driver programming for an enterprise. (e.g. advantech ISA-card).
This was my first project of that kind and it worked immediately.

Arduino will not be that different.
I never worked with arduino. But when there are some coded examples I easily understand.

(I've programmed assembler on Commodore vc64 already when I was very young. E.g.: My printer had 7 needles but the bitmaps had 8 bits/byte. So I wrote a routine in assembler that found the grafic memory and transformed the bitmap for my printer. The program was used by many. It has been copied many times.)

FULL SUCCESS!

Everything works!
The arduino mini plus 168 3.3v sends through bluetooth the data of the honywell compass to the n900!

(After a mistake with my reset line everything went very well.)

The seller on ebay had a link to the arduino libraries for the compass. There was a useful example and it compiled well for the arduino.

There was a script at
http://www.dasskript.com/wiki/the_arduino_and_the_n900

It worked perfectly with my adapted mac adress on the n900.

Now my n900 shows the directions of my bluetooth compass.



... and what's the best:
I didn't find a suitable little 3.3v battery.
So finally I bought a very cheap china gadget:
A solar key chain with light: 3.7v.
It did open easily (no screws, no glue).
The solar module has the size of the arduino (1/3 of a little match box.)

Now my arduino works with a solar battery.

The whole construction can easily be put into a match box.


What is missing:
- A beautiful compass application
- system integration of the compass


Prospective:
Now I can add every sensor or i2c device I want. (E.g. gas sensor, temperature, balance, adapter to garmin...)

That's the joy of FOSS, be it software or hardware...

Anyway, maybe You shall consider contacting developers of Marble for N900, if they can collaborate with You, to support compass readings? It would be great addition to navigation, and Marble seems to most actively (and most competitively) developed map/navigation application for N900.

Second thing - for a long time, linux desktop users (that have legacy COM ports) can easily solder on their own a InfraRed sender/receiver, which gives possibility to record IR signals, and create "templates" for certain Ir devices (pilots, basically) - that can be used on devices with IR sender, like N900. Unfortunately, most of the times this doesn't work via COM to USB adapter.

Would it be "doable" (well, with reasonable effort) to create IR receiver/sender, that communicates with N900 via bluetooth?

Last but not least, is it do-able to communicate with N900 via USB (hostmode, H-E-N), instead of bluetooth?

Nice project. Isn't compass supported through Qt Mobility API?

@Estel

It's an arduino (Hardware platform for noobs): Of course you can connect it by USB. Its a primitive serial connection (works as client or host).
I didn't do it:
- a) because cables are not cool
- b) I am a complete noob in hardware and I didn't want to hurt to my n900 (600$) by a false Voltage on my arduino mini pro (20$).

Infra red is in every low cost accessory kit for arduino together with a infra red remote. (So its lirc and not irda: not very fast).


@Ivgalvez
Even if compass is supported by QT-Mobility-Framework:
- How do I tell to the framework to recognize my compass?
- Not all applications use QT-Mobility. (Does OVI-maps?)