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.