My question is will I need to pick up a logic level converter to correctly hook up these sensor modules to the arduino? I know the barometer from adafruit has one built in but I couldn't find information on the other two being that they are off brand.
Also, will I be connecting the scl and sda of all three modules to the same a4 and a5 pins on the arduino?
The Pro Mini has no pullup resistors connected to SDA and SCL. You will need to add your own. If you put them to the 3.3V line, then there's no voltage conversion required. 3.3V is just high enough to be interpreted as a logic HIGH by the 5V Pro Mini.
Make sure you power the BMP180 from 3.3V and its own pullup resistors are probably all you need.
That is the standard level converter (and thus the one on the Adafruit BMP180 board) for I2C (and many other applications) available for less than a dollar on eBay - I bought a dozen or so just recently (but of course, have yet to use them in anger). Note these particular ones include a 3.3 V regulator!
Grumpy_Mike:
If it were me I would also disable the internal pull up resistors in software or use a library that does not enable them by default.
Given that the software is written such as to only enable the internal pull-ups and never writes an output HIGH, it would be sufficient to clamp the lines to the 3.3 V rail.
mumbleelbmum:
If I'm not mistaken, it appears that all the modules have a regulator.
If you were referring to the I2C level converter modules on eBay, there are about three versions; the one I cited above with two (passive, as are all these) level converters and a regulator which incidentally means they cannot be used for 1.8 V logic in case that were a point, one with two active bidirectional level converters and two resistive dividers (I don't think that would be all that useful) and four-way level converters that I cited in this other thread.
Actually, I think I saw eight-way ones there also, useful for level converting a whole parallel byte.
Probably also knock-offs of Adafruit's active level converters too.
I will do you guys a solid and Google the crap out of these modules. Particularly the off brand boards that seem to have no datasheet anywhere.
I will post all info I find regarding their specifications.
Than I will work up a schematic of my own displaying how I think they should be wired. That way it will be a simple go or no go from you guys.
I plan on etching my own pcb to encompass these sensors into a shield for the pro mini. I have no laser printer and no developing equipment. Is there any other ways to produce good work? Precision sharpie? I don't mind if it's time consuming...
The best way to get a custom PCB is to get the professionals to do it. You can get turnaround times of 2 weeks or less at only a few dollars per square inch. I use OSHPark a lot. There are a lot of other services out there. Try to choose one that lets you upload "Gerbers" or CadSoft Eagle files. The ones that have their own design program (like Fritzing) lock you in to their system, and should be avoided even if the actual PCB output is good.
Eagle seems to be a pretty good standard in the hobbyist/Arduino community. There's lots of support for it and most of the popular open-source designs from SparkFun, Sainsmart etc can be opened directly in Eagle and modified by you. The size restriction of the free version of Eagle is not usually a problem for 99% of hobbyist projects.