Transformers

[RJ_Make]

Looking for very small 220vac to 3.3vdc transformer module. I have a project that involves controlling 2 220V water heaters. The project box is fairly small, so the smaller the better.

[Mrlynx]

something like this?
http://www.ebay.com/itm/AC-DC-Power-Supply-Isolation-module-Input-AC-90-240V-Output-DC-3-3V-500mA-/251365063335?pt=LH_DefaultDomain_0&hash=item3a86867aa7

[jendrush]

Maybe small usb wall charger for 1,4$, and regulator from 5V to 3.3V for 0,1$ would be good solution?

[RJ_Make]

@Mrlynx That looks like it might work.. Thank you!

[RJ_Make]

@jendrush I think it would be to large, and I've not seen a 220v version before.

[Damme]

@ServiceXp I've been looking at things like this http://www.digikey.com/product-highlights/us/en/cui-vsk-series-encapsulated-ac-dc-modules/853

[Damme]

There are smaller things too, http://www.cui.com/product/resource/pbk-3.pdf but I don't like the clearance on that component. and it has no temperature protection.. But there are tons of things to choose from. tell me if you find something you like.. :)
Digikey search

Edit; NOTE:
If you are playing with mains BE CAREFUL about if you are buying a insulated one or not, You could have something like ~225v on your 0v and ~230v on 5v and if you touch this you will smoke.

[RJ_Make]

@Damme Awesome set of options. Thank You!!

Thanks for the warning, I'm a newb to electronics/arduino, but am very familiar with high voltage equipment. (HA-HVACR Tech.)

[Zeph]

@jendrush said:

Maybe small usb wall charger for 1,4$, and regulator from 5V to 3.3V for 0,1$ would be good solution?

For some projects, using cheap chargers can be a good option. However, I'd open any such cheap charger and have a look before using it. Some appear to be acceptably designed, and some appear to be dangerous designs, from the teardowns. For example:

http://www.righto.com/2012/10/a-dozen-usb-chargers-in-lab-apple-is.html

He rated 2 out of the batch as downright dangerous.

Even with one which appears to have a reasonable design with enough separation, I would not be poking around in the sensors or PCB while they are currently powered from 230V with a cheap charger. Unplug first. And if you need power for programming or testing, use your normal USB supply (eg: a laptop or a high quality power supply) or batteries. Maybe that's just me, but this seems like a reasonably easy additional precaution. Even if the PCB has good separation, the insulation between windings of a transformer could be marginal, for example.

Most readers here probably already know this, just thought it was worth noting for anybody coming to this hobby more recently.