Powering Microcontrollers

Discussion in 'Embedded Systems and Microcontrollers' started by witchdr, Oct 27, 2010.

  1. witchdr

    Thread Starter New Member

    Oct 27, 2010
    2
    0
    Hi,

    I'm new to this forum (and Microcontrollers) but have recently purchased an Arduino and have made a few simple fun things with it.

    A particular area of interest to me is home automation and I'm wondering how manufacturers power their microcontrollers from mains power whilst still making the devices small.

    X10 modules, for instance, are very small but presumably use low voltage microcontrollers for the logic but there is no room inside the device for the typical 5v mains power supplies used for consumer electronics.

    I've searched the internet and component supplier websites but I don't think I've hit upon the correct keywords.

    Can anyone tell me what kind of thing I should be searching for. Basically I'm after a very small 9v (or maybe 5v) PSU.

    TIA

    Andy.
     
  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    Usually 2 1220 button cells, or 2 2032 coin cells in series, followed by 2 diodes works well for a 3.3-5V processor, it isn't regulated, but will work. 3 of the 1.5V button cells, such as LR44 will also work, less the diodes.

    Add a capacitor in parallel with the battery to keep the supply stable during load switching.

    Best way is to use 3 AA batteries, but to get smaller, you can't beat button cells for low power apps and portability.
     
  3. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
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    You are looking for a mains adapter for your micro controller?

    Look into the LED lightbulbs and CFL lightbulb circuits.

    These use micros, very often, and all the circuitry is usually fitted into the base of the bulb.

    You need a switcher IC, an inductor, and a cap, and 4 diodes

    Here is a little one I use. It rectifies the AC to DC then gives me a nice steady output.

    I am using this for constant current, but you could just switch the regulator to 5v for your uC.

    It is only .5" x .5" less the leads
    [​IMG]

    [​IMG]

    By the way, there is no need to mention that I should be a hand model..I already know. ;)
     
    witchdr likes this.
  4. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Nice idea, but does it give you isolation from the mains? Oops, forget I asked.

    John
     
  5. t06afre

    AAC Fanatic!

    May 11, 2009
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    A cell phone charger with an output in range 4.5 to 5 volt may also do the trick. For the hobbyist I will always recommend using approved equipment then connecting to the mains. And rather swallow your pride then it comes to the desire for small and neat. A small cell phone charger is almost the size as the socket plug. And nobody will notice it.
     
  6. retched

    AAC Fanatic!

    Dec 5, 2009
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    Right after you connect it to a 1:1 isolation transformer.

    And who in there right minds WOULD NOT USE A TRANSFORMER FOR SAFETY?

    A transformer can turn a funeral into an uncomfortable shock. Use them.
     
  7. Potato Pudding

    Well-Known Member

    Jun 11, 2010
    684
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    I have seen it mentioned that some are so low power that just using a tiny bridge rectifier, a high value dropping resistor, a zener and a capacitor, and they will generally work pretty well. I haven't tried it and I think I would elaborate on that for a circuit I was building.

    It defeats the purpose of the low power rating horribly to just resistor drop 110 volts even if you are only drawing 100uV.
     
  8. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Also, you need a pretty huge cap to filter 50/60Hz.

    Hence the switch mode power supplies that are getting down to the size of the plug in itself. 5V/3A output, no less, and extremely low drain when idle, the isolation transformer is on the high frequency side, rather than the line side, so the heavy/bulky 50/60Hz transformers and huge caps are a thing of the past.

    Try them out! Nearly FREE at garage sales or 50 cents from thrift shops. Since most models of phone need a different charging jack connectors (to force more add-on sales when the user upgrades/changes phones or PDA), there are literally millions of 5V/1A+ adapters floating around that won't plug into anything modern.

    Just cut the plug off, use the power, it's the trifecta of cheap, easy, and safe.
     
  9. witchdr

    Thread Starter New Member

    Oct 27, 2010
    2
    0
    Thanks for all your replies.

    This looks like the closest thing to what I'm looking for.

    Could you provide some more details. I'm still new to electronics and need a little more spoon-feeding if you could spare the time.

    Although I haven't had my Arduino long I'm already looking at some custom circuits using uCs. Whenever I see something useful, like X10, then look at the price I can't help wondering if I can't make something myself :). Although I'm looking at an RF solution at the moment.

    I'm theorising at the moment and wouldn't install anything in my home without ensuring it was safe.

    I'm sure QVC will be phoning any day now. :)
     
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