So my bedroom light is a dimmer, and I'd like to be able to externally control it with Arduino in addition to the switch on the wall. So I was thinking, if I replace the main switch with a button that the software uses to toggle an internal relay at each press, and then replace the dimmer slider with sparkfun's motorized slide pot, that would work as long as that kind of pot will work with AC. If not, which I kind of doubt it will anyway, how can I get it to work?
Please do not play with mains. If you have to ask such a question you are not ready to do it.
Wiring up mains electricity without a clue about what you are doing is dangerous and can lead to death or fires.
Well duh... I'm not an idiot; I'm asking advice so that I can know what I'm doing.
Notice how I said I doubted it would work, implying that I already knew I was stumbling in the dark and was planning on not moving anywhere until someone gave me some light to work with, so I don't trip and fall on something dangerous. Like high voltage AC current that I'm well aware could kill me.
Like high voltage AC current that I'm well aware could kill me.
Yes I am sure you are.
What you are not aware of is the sorts of things you have to look for in terms of isolation from the mains to your system. The regulation creepage and clearance and leakage.
That is something that you can't just learn from a few words on a forum, that is something you need experience of or a lot more information / knowledge than you have now.
that would work as long as that kind of pot will work with AC.
If you don't know that all pots will work on AC then you don't know enough to do this project. While the pot will work, how safe it will be depends a lot on the design and construction of the pot, something you can not tell from the description on a sales page. You need to go to the data sheet on the actual pot but even that might not tell you.
What you would have to do is to measure the leakage between the pot and the housing, I suspect you do not have the equipment to measure high voltage leakage, I know I don't.
Hi Squirt,
Looks like someone is a bit more grumpy today than usual.
If all you wish to do is dim a 240V globe, and you want to incorporate an Arduino, why not use a dimmer with the shaft controlled by a servo motor, and you still get to use your 10K pot.
This way there's no risk of hurting yourself.
Ken
If you connected your AC through a 10k pot and then to a lamp, you would get 0.024 amperes.
Not many lamps will work on that, except a tiny led. That circuit would not only be risky and dangerous, but pointless.
Different types of dimmers are required for different types of lamps. Traditional incandescent lamps use a triac circuit. For other types, it is more complicated. Many kinds of lamps have no practical dimming method.
The brightness of leds can also be controlled by PWM, using DC, not AC. That is why most leds used for lighting, have a DC power supply.
First, you need to find out what sort of lamp you have.
Then, I suggest that you visit wikipedia, and read about triacs, and follow all the links at the bottom of the article to further information.
Then, I suggest that you google "triac dimmer", and makes notes of all the images that come up, and follow those images to the websites they came from, and read what they say. And, if they use some words you don't understand, look up and understand what all of those words means.
Then, I suggest you repeat the previous step with the words "arduino lamp dimmer", and carefully study all the links that come up.
This will probably take you several days to absorb.
You might want to then google "arduino lamp dimmer kit", and examine the results of that.
You young folks have no idea how hard this was 30 years ago.
Why reinvent the wheel. There are remote controllable dimmer switches available. Visit the lighting department of your favorite home improvement store. There devices have been availabe for more than 50 years.
I'd say leave your bedroom light alone, its quite boring in comparison to what you can do with LED's.
Cover your ceiling with LED's, grab a DC power supply and a handful or arduino's and go crazy.
Hey; thanks all for the responses!
@neksmerj yeah sorry, I just didn't feel like Grumpy_Mike's first answer was really helping anything and was negative feedback. Through some later thought, I came up with maybe trying to do something similar to what you're suggesting; it could quite possibly be what I'll end up doing.
@oldcoder yes, that was also something I thought of maybe trying to do, but I forgot to mention I don't have a lot of spending money on hand and if I remember correctly, those things are fairly expensive. (Please correct me if I'm wrong though, because they could be very useful if I can afford them!)
@Paul_au Hmmm... I hadn't really thought of just replacing the light with LEDs... I'll give that some consideration as well; thanks for the idea!
@Grumpy_Mike @michinyon @Runaway Pancake yeah I'm beginning to see how complicated this is... thanks for letting me know before I put too much time into such a seemingly simple project. Like I said I'll probably end up dumbing it down by using an external servo or switching to DC LEDs.
Followup question on that: If I do end up switching to LEDs, could I not just have a wall-wart soldered to the wires that the switch would be connected to such that there is always power to it, and put the DC end to the Arduino to have the same effect of being run off house power? (And then just never plug anything into the outlet it controls?)
I'm bumping this because I came back to planning for this project and would like a yay or nay for the followup question I had in my last response, thanks 
Sketch that out, let's see a diagram.
@Squirt_ covering your lights with LED's and controlling them with Arduino's, although cool, is pretty much pointless. It's like putting colored lights underneath your car. If that's your cup of tea then go for it. I like to use my Arduino's and electronics to make my life either easier or add a feature that will be useful often.
I have built a laptop stand with a 120mm fan that runs off 110 VAC... it came off a 460 VAC Baldor 1 HP motor. Someone in Maintenance thought it would be a good idea to put a 110 VAC fan on a 460 VAC motor...(I'm in Engineering by the way,) so I took the fan home and made it useful. I constructed a laptop stand but the fan is so loud, you almost need a potentiometer to control this thing for noise ordinance alone. I have an Allen-Bradley 10K pot and I have tried to add resistance to both the neutral and the hot that goes to the fan motor and nothing happens... so if your looking to dim a light, or something like it, just using a pot will not reduce the current going to your load. If you can get it working, just with those items, please let me know because I just spent 2 hours trying it out and smoked 2 pots and reset my breaker 5 times just trying different configurations and yes I do have a degree in Electrical Engineering and playing around with 110 VAC does not bother me when you know your on a 15A breaker and work with 460 VAC everyday and certified up to 13,600 VAC.