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This might be a really simple rookie question.

I (who am very new to electronics) need to be able to switch a 24 VAC line on/off using a DC signal coming from an Arduino. Google searches have been fruitless (but then, I don't really know what to search for). If someone could point me in the right direction.

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  • \$\begingroup\$ How much current? Is the 24 VAC floating relative to the DC control signal? \$\endgroup\$
    – Phil Frost
    Commented Jul 31, 2013 at 11:56

2 Answers 2

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The easiest way is to use a solid state relay. For example, this part from digikey: http://www.digikey.com/product-detail/en/S212S01F/425-2412-5-ND/720407

Then wire it up like the schematic. I used an LED as an indicator so that when the SSR is on, you will know. If you don't need it, then just resize the resistor. The SSR suggests operating at 16mA from the datasheet.

Assuming arduino is outputting 5V, SSR has 1.4V drop, and LED has 2V drop.

So with LED indicator:
(5V - 1.4V - 2V)/100 = 16.mA

So without LED indicator:
(5V - 1.4V)/200 = 18mA

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ The digikey part you are linking to is rated for 12A/220V. OP hasn't said how much current he's trying to switch, but I reckon it might be overkill in terms of performance and price. \$\endgroup\$
    – us2012
    Commented Jul 31, 2013 at 13:31
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Use MOC3043 with triac: http://www.fairchildsemi.com/ds/MO/MOC3043M.pdf Decrease proportionally current-limiting resistor.

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