Hacked Gadgets Forum

March 13, 2008

Opto-Isolated TTL to 110 VAC Power Source

at 5:26 am. Filed under Electronic Hacks



Here is a simple hack to convert a simple (cheap) module into your very own opto-isolated TTL to 110 VAC power source.  Since it is isolated you can control it with low voltage circuitry and have no worry about electrocution. The other concern when you control high voltage with a low voltage control circuit (a computer parallel port for example) is that a failure could cause high voltage feedback which could damage your delicate low voltage gear, have no fear with this circuit since there is no physical connection to the high voltage side from the low voltage side.

"Light-controlled outlets are normally used to light a nightlight when it gets dark. By mounting a red LED directly above the light sensor you can use any digital circuit to drive a 110V load safely opto-isolated from your low voltage control circuit. This Instructable shows a 2-channel module built into an outlet box, but the concept can be expanded to any number of channels in any packaging format. I use a pair of compact 8-channel modules to drive an outdoor Christmas tree display using a Basic Stamp microcontroller.

The light sensor inside these devices is a cadmium sulfide (CdS) light-sensitive resistor which is most sensitive to red-orange light, so light from a low-output red LED is sufficient to make the outlet turn on. The LED can be driven from any control source.

This Instructable shows you how to modify the light-controlled outlet, converting it into a simple module that has a pair of wires for 110V control and a pair of wires to drive the LED. If you don’t want to do the "circuit bending" required to make this module, you can use the light-controlled outlet as-is by merely mounting the LED over the sensor externally. Then you can plug as many modules as you want into a power strip and run your LED wires to a suitable controller."



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5 Responses to “Opto-Isolated TTL to 110 VAC Power Source”

  1. Project_Nightmare Says:

    So this is basically a solid state relay???

  2. jordan Says:

    No, this not the same as a solid state relay. This is a light controlled variable resistive circuit…Cadmium sulphide photocells have an on resistance of 1k ohm. This means your maximum current per switch is .12 amps, which works out to about 14 watts. A solid state relay has an on-state resistance of almost 0 ohms and can handle 10 amps or more.
    This circuit is useless for controlling anything other than a few lights – you couldn’t even power a laptop with this.

  3. mrmeval Says:

    It’s a nice proof of concept but in the comments is mentioned this MOC301XM and MOC302XM

    O.K. very interesting
    but I make more with my commodore 64
    I control 800 light / by 16 line of 8 bit
    with a moc 3010.”

    Unfortunately he’s put his video on a ‘must register’ site and I don’t link to those.

  4. Michael Says:


    The load is not running through the CDs cell. The CDs is controlling what looks like an SCR. There’s no way you’d put 14W through that cadmium sulfide cell. What he’s doing is simulating day/night light levels with an LED to CDs cell interface. It’s a clever hack that keeps the low voltage homebuilt stuff isolated from off the shelf AC power handling.

    You could control anything that the original plug could handle (you wouldn’t want to power a laptop with this anyways).

  5. response-guy Says:

    I’m looking for a commercially built gadget like this that can be controlled programatically. Looks like I’ll have to build it…

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