Hiya. :) (..and ground question with mixed AC, DC)

Discussion in 'General Electronics Chat' started by 1010101, Oct 25, 2009.

  1. 1010101

    Thread Starter New Member

    Oct 25, 2009
    Hiya. Been reading here for a while and now I'd like to jump in. :)

    It's been 20+ years since the last electronics in college. I've been interested in this stuff since I was a kid (got a bunch of LEDs from Radio Shack for my 10th birthday, had no idea that I needed to limit the current and burned through them pretty fast, but it was fun :D ). And now that I have the money to support this habit, I've been reading up (working through the ebook on this site, as a matter of fact. Good stuff.) and buying a lot of the basics (DMM, small power suppy, wire, etc), including the microcontroller kit from sparkfun.com.


    I was reading the EL-wire driver tutorial here. They're using triacs and the output from a microcontroller to light electroluminescent wire with a battery powered inverter.

    My question is about the attached bit of the schematic (also in the linked article). It looks like the inverter and the microcontroller share a common ground. If they don't, I don't see how the output from the uc can turn on the triac. And yet, it seems like a good way to fry something to put the inverter output on the same ground the uc is on.

    What am I missing?
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    If the intent is to make a circuit which controls a Load tied across the AC powerline, then the entire circuit can be build so that it is referenced to one side of the AC line, usually Neutral (in the US and Canada). Lots of products are built this way; think of a AC dimmer you install in your house.

    HOWEVER, this is a really bad idea for hobbyists to build circuits that are hard-wired directly to the AC line. It is much safer to build/work on circuits that use a transformer-powered low-voltage power supply that is isolated from the AC line, and where the final output device is an electomechanical relay or an opto-isolated solid-state relay.
  3. 1010101

    Thread Starter New Member

    Oct 25, 2009
    No, in this case it's just a battery powered inverter to step the 3V or so up to 125V at something like 400+Hz to drive the EL.

    More reading since I posted this, it looks like this is a "low side switch" configuration. But it still bugs me that the uc ground and (I guess) the inverter output (neutral?) are shared. Wouldn't it be better for noise, if nothing else, to have the power side optically isolated?
  4. russ_hensel

    Distinguished Member

    Jan 11, 2009
    Might be better to isolate, but I have used the above circuit, and had trouble only with noise which I was able to deal with.
  5. 1010101

    Thread Starter New Member

    Oct 25, 2009
    Thanks. :)