I want to collect everything about I2C level shifters here: http://arduino.cc/playground/Main/I2CBi-directionalLevelShifter
Feel free to add to that page.

The function twi_init() in twi.c enables the two internal pull-up resistors.

If a 3.3V I2C device is connected to the 3.3V, and the Wire library is used, the SDA and SCL lines have the internal pull-resistors to 5V.
Some low power I2C devices might have problems with that.
Allthough it should have open-drain or open-collector, according to some datasheets, the SDA and SCL may not exceed the 3.3 or 3.6V.

I have mentioned this also here: http://arduino.cc/playground/Main/I2CBi-directionalLevelShifter  (search for the word "violate").


This forum question is about the internal pull-ups: http://arduino.cc/forum/index.php/topic,105196.0.html

We should be able to use the Wire library for 3.3V components.
So I have posted this: http://arduino.cc/forum/index.php/topic,105291.0.html
I think that the wire library should change (replies about wire library with that topic please).

I wrote a page about level shifters in the Playground section: http://arduino.cc/playground/Main/I2CBi-directionalLevelShifter
And I checked the Wire library, it does indeed set the internal pull-ups to 5V. I've started a new topic about that: http://arduino.cc/forum/index.php/topic,105291.0.html

Added to playground: http://arduino.cc/playground/Main/ThermalAnemometer

It's needs some beautifying.
I have also added a link at the environment section.

The bus pirate uses a PIC processor. If you can find the right software and libraries you might try it. But I have no experience with PIC processors at all.

This is the link? : https://store.diydrones.com/Full_ArduPilot_Mega_kit_from_Udrones_p/kt-apm-02.htm
If you buy that you have: absolute pressure sensor (barometer), gyro, accelerometer, GPS.
That's only 4 sensors, for a high price.
If they come with good explanation and libraries, you can have it working in a short time.

I think the TinkerKit system in the Arduino store is cheaper.
You can use a normal Arduino Uno, so things don't get unnecessary complicated.

The accelerometer and gyroscope can be the same thing. I have ordered such a sensor myself, so I'm still not sure how they can distinquish between accelerometer and gyroscope 

I just wrote this: http://arduino.cc/playground/Main/I2CBi-directionalLevelShifter

The 3.3V is an output.

If you use pull-ups on the I2C bus to the 3.3V (NOT the 5V), it is a little compatible with 3.3V.
I'm writing a playground article about level shifting right now: http://arduino.cc/playground/Main/I2CBi-directionalLevelShifter

1)  The I2C is designed to have one single master, with many slaves. You only need SDA and SCL (both will pull-up resistors) and you can attach many slaves. Every slave reacts if its ID is transmitted on the bus. But if some sensors use 5V and others use 3.3V, you need extra hardware for level shifting.
2)  Simple sensors like sensors with analog outputs (MMA7361 accelerometer), or sensors with a single digital line (DHT11, temperature + humidity) can be connected to the Arduino directly.

If you want to use the MMA7361 accelerometer, you need 3.3V again. But you need 3 analog inputs.
The digital version MMA7455 is also running at 3.3V and can be attached to the I2C bus. So you use less pins, but you need an example or a library to get the digital communication working.
These MMA... series accelerometers are cheap. Many people use the BMA... series accelerometer which are more expensive.

The whole tinkerkit idea is to have a shield, and with connectors and cables you can attach sensors. It is very fast (just click the shield and cables) and the result is very nice and clean looking.
But to test or develop something by yourself, you could solder the sensors yourself and learn about them along the way.

Thanks for posting the result.

The second mosfet should be connect to ground 
But the minus of the USB Battery to Vin ? That can't be right.
Why not use the voltage of the  8*1.5V batteries to Vin?
The Arduino uses little current, so the voltage regulator of the Arduino won't get hot at 12V.

Wikipedia about fluorescence: http://en.wikipedia.org/wiki/Fluorescence

I assume that for fluorescence, you use a UV light source, and that there is very little light.
So you need a very sensitive sensor.

S9706: 12-bit
S11059: 16-bit
Both are for 3.3V.
The datasheets are hard to compare, since the sensitivity is in different units.
But the S11059 has a larger range of colors, and is more sensitive.

However, if it's sensitivity is enough to detect fluorescence colors ? ... I don't know.
You have to try that, or find an example of someone who did that already.

To interface all of that, you need some kind of microcontroller. Do you know something simpler than the Arduino?

There are shields (boards you can attach to the arduino) with sensors. Most of those shields have example code and a library.
You could start with a shield with as many sensors as possible.

Sensors with analog outputs are easier to read than a digital serial communication.
So, you could try to find sensors with analog outputs to make it yourself easier.
But if you need all those sensors at the same time, you don't have enough analog inputs.

(1) If you have a Arduino (for example the Arduino Uno), start with the example for a blinking led.
(2) Try to send a message back, with the Serial library.
(3) Try to interface an analog sensor.
(4) Try to interface digital sensors over I2C or other digital serial communication.

It's not hard. The only problem is that most sensors use 3.3V. But the Arduino has 3.3V onboard for those sensors.

Looking good.

The gate voltage is now 10/11 of the output of the Arduino. The IRLZ44N needs 4V in this situation, so you're fine.
The ground current of the battery-motor-mosfet part could influency the Arduino or the gate voltage. So don't use thin wires and make solid connections.

The normal current for the optocoupler led is 20mA.
This 20mA for the led will put the transtor into saturation.
But in your schematic, 10mA for the led is also enough.
At 20mA the forware voltage over the led is 1.1V (see the datasheet).
You have a current of (5-1.1)/220 = 17mA -> perfect.

Yes, this one is okay for you.

As far as I know this relay has 5 pins. Two for the coil, and three for the switching contacts. That is why the header has three contacts. You just need two of them for switchting something on.