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I have an arduino board, and I would to turn a different, completely isolated circuit, on and off. Actually, I will be running 230V to another device, and then control whether it is on or off, with the arduino.

http://www.powerswitchtail.com/Pages/default.aspx I have been looking a bit at these, and it looks interesting. The problem is, shipping to Europe means they become quite expensive.

So how can I make one myself? Do I need to build some kind of relay? What components can actually handle sending 230V through it, but be controlled from arduino's 5V?

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  • \$\begingroup\$ How often do you want to switch the load? What sort of load will you be connecting? Relays work very well for pretty much any load, but they are mechanical devices that are prone to wear under frequent high-load switching. \$\endgroup\$ – Mels Jan 31 '14 at 12:40
  • \$\begingroup\$ If you need to switch often and your load isn't heavily inductive or capacitive (motors, switching power supplies etc.), a Solid State Relay (preferably one with optical isolation) would do the trick without any moving parts. \$\endgroup\$ – Mels Jan 31 '14 at 12:41
  • \$\begingroup\$ Actually, simple relays driving 230V load but controlled by 5V MCU existed a long time ago, nothing fancy. \$\endgroup\$ – Pyxzure Jan 31 '14 at 12:52
  • \$\begingroup\$ I will be turning heating elements on and off quite a lot. \$\endgroup\$ – Nicolai Jan 31 '14 at 12:56
  • \$\begingroup\$ Several of the components in the schematic @jrtrzeciak linked to are not recommended for 230V so don't buy the 120V one. \$\endgroup\$ – Pete Kirkham Jan 31 '14 at 14:08
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It looks like they used to sell a kit. There is a schematic near the bottom. A relay of some sort is your best bet. Just be sure it can handle the current and voltage requirements. Also, be mindful of how much current the relay coil will need to operate (unless you use a solid state relay). You may need a transistor in between the Arduino and relay to amplify more current.

As always, be extremely careful when dealing with high voltages and current. Do no undertake this project until you have done thorough research of what safety precautions you need to take.

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  • \$\begingroup\$ So, solid state relay is what I will need to investigate further, right? \$\endgroup\$ – Nicolai Jan 31 '14 at 12:56
  • \$\begingroup\$ Correct, as @Mels mentioned, there are no moving parts, so they are less susceptible to wear. I don't have enough experience with them to say whether they are for sure the best bet for your application or not though. \$\endgroup\$ – Justin Trzeciak Jan 31 '14 at 12:58
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    \$\begingroup\$ Solid state relays are generally much more expensive, but also much more reliable. However, a well-selected mechanical relay can also last for years and years. Be sure to examine the datasheet of the relay you're considering very closely, and apply large tolerances to increase life expectancy. For example, if the heating element draws 5A at 230VAC, go for a relay that's capable of switchting an active load of 10A. \$\endgroup\$ – Mels Jan 31 '14 at 13:08
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    \$\begingroup\$ One very important consideration is that when a solid state relay fails, it usually fails in a conductive state. That might make them very undesirable in your case, especially if your heating element is capable of causing a fire. At the very least, put a thermal fuse in series with the heating element such the it would cut the power if the temperature goes above normal levels. \$\endgroup\$ – Mels Jan 31 '14 at 13:14
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    \$\begingroup\$ Here's a great article comparing the two technologies in relatively simple terms: electronicdesign.com/components/… \$\endgroup\$ – Mels Jan 31 '14 at 13:15

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