I’m a newbie and don’t own an Arduino yet. I’m looking for a way to control multiple 120V AC circuits, basically switch them on and off like a timer, but more quickly (every few seconds) and independently following a pre-set program. Don’t need to supply more than an amp or two on each circuit. Would the Uno be able to do this, and what additional items would be needed? Thanks for any info!
How many is multiple ? Something like this combined with an Arduino might be a start.
Sorry, I mean three or four. Thanks for the link!
there are basically 3 approaches. 1) mechanical relay (as in the previous response), 2) triacs or 3) Solid State Relays (SSR).
Use relays if you are switching the circuit on/off infrequently. Use triacs for quicker switching. Also, a lot of relays will make a noise when they switch, not terrible but depending on your application you may want it to be quiet. Triacs are silent. You also want to consider switch ratings of mechanical relays - typically, they are rated for a certain number of cycles (mechanical and electrical). A typical relay is rated for 100K electrical operations at a certain current/voltage and if you switch it once a second, you will use up the life span in less than 2 days. Triacs also allow power control (dimming) if that’s of interest. Here’s a link to a arduino discussion http://www.arduino.cc/cgi-bin/yabb2/YaB … 1276992650
SSRs are basically on/off triacs. Not cheap but pretty easy to use. You get good isolation with them. Here is a sparkfun kit http://www.sparkfun.com/products/10684 but I wouldn’t use it because of the design problems called out in the comments.
I’m not sure I would use the robotshop relay shield though - the thought of putting 120VAC that close to digital electronics makes me nervous.
I agree with all of the thoughts expressed and only note that it's *claimed* that the relay above uses SSRs. I couldn't see the part number on the relays to verify or refute that claim.Philba:
I’m not sure I would use the robotshop relay shield though - the thought of putting 120VAC that close to digital electronics makes me nervous.
I use solid state relay - module with screw terminals that are physically restricted by a cover from accidentally touching them. Lots of these available 'round the 'net and eBay, inexpensive.
Mee_n_Mac:
I agree with all of the thoughts expressed and only note that it's *claimed* that the relay above uses SSRs. I couldn't see the part number on the relays to verify or refute that claim.Philba:
I’m not sure I would use the robotshop relay shield though - the thought of putting 120VAC that close to digital electronics makes me nervous.
I didn’t get that it used SSRs. I saw the “photo coupled” comment but not sure that implies an SSR. It would be overkill to use an opto isolator with mechanical relay so you may be correct. Still, my concern with that board is lack of physical distance between 120VAC and the rest of the system. SSR modules that are separate from the 'duino is a better approach. 120VAC is nothing to take casually. A 120VAC shield is just plain a bad idea.
Personally, I would get an electrical utility box and mount the SSRs in it along with the controlled device connections. I’d put the 'duino in a separate box and use a wire bundle (a length of cat 5, probably) to connect the two. Secure the wire both places where it exits the boxes. Use rubber grommets to prevent wear.