i want to read the electrical appliances state.so i need to convert 230v to 5V dc.Is there any easiest way to convert voltage from 230 to 5V.
I would use a 230 V AC relay.
Hi,
Use a USB power pack, its insulated from 230Vac and most can supply the 5Vdc at 1A if needed.
Tom.. 
anbu123:
i want to read the electrical appliances state. so i need to convert 230v to 5V dc.
Those two statements do not make sense one does not follow on from the other.
What do you want to do and what do you mean by “state”? And why do you think converting the mains to 5V will help you do this?
A series resistor ( 2 x 100k in series ?) shunt diode ( 1N4148?) and optocoupler would allow you to sense the presence of 240vac safely....
Allan
A relay is also a simple and safe solution.
is there any other alternate optocoupler available??
anbu123:
is there any other alternate optocoupler available??
There are many. I just chose that one because the datasheet made it seem like a good candidate for reducing R1 to where it could be a 1W resistor (because it has a nice, high, CTR). Otherwise it was going to be a 2W or even 5W.
How about 4N35, which has a CTR of around 50% for lower IF currents (at room temperature). So, for this one, I would increase R3 to 10k, which should allow R1 to stay the same.
Caveat: (and I should have included this on my original reply) I haven't tested this, so no guarantees -- it's just meant to stir the pot, so to speak.
There are optocoupler specific for AC, es. sfh620a, but don't know if is useful in this specific case.
Ciao, Ale.
anbu123:
i want to read the electrical appliances state.so i need to convert 230v to 5V dc.Is there any easiest way to convert voltage from 230 to 5V.
...
is there any other alternate optocoupler available??
Also, I had nothing better to do, so I went with an interpretation of what you are looking for, but you still haven't elaborated in a way that any of us can be sure of what it is you really want. Grumpy_Mike is correct that your "state" statement is rather vague and meaningless.
I refer you to the "Rules" of this forum: How to use this forum - please read - Website and Forum - Arduino Forum
Use a capacitive/resistive dropper to power an optocoupler, not just a resistor, then you don't have
to dissipate lots of heat.
A 68nF X-class cap in series with 10k 0.5W (fusible resistor) will bring 240V down to 5mA or so with
only 0.25W dissipation. If the cap fails short the resistor will fuse before the opto-coupler is damaged
(it will take 6W or so and pass 25mA). You must ensure the opto coupler is AC or has a backwards diode across it.
Reducing the heat loss is usually important as mains circuitry is enclosed for safety and little cooling
is available. Using the right rated components (like X-class caps) is very important in preventing
risk of fire.
A single resistor across the mains is a bad idea as if it fails an arc could envelop it and cause huge
fault currents - having several components in series limits the chance of heavy arc unless something
like lightning is involved In evaluating safety assume every semiconductor will fail, rely on passive components if you can.
The datasheet for a fusible resistor should explain the circumstances under which it fails (open) without
causing a fire. Typically 10x -- 30x overload or so. For instance http://www.farnell.com/datasheets/2045763.pdf
MarkT:
Use a capacitive/resistive dropper to power an optocoupler, not just a resistor, then you don't have
to dissipate lots of heat.A 68nF X-class cap in series with 10k 0.5W (fusible resistor) will bring 240V down to 5mA or so with
only 0.25W dissipation. If the cap fails short the resistor will fuse before the opto-coupler is damaged
(it will take 6W or so and pass 25mA). You must ensure the opto coupler is AC or has a backwards diode across it.Reducing the heat loss is usually important as mains circuitry is enclosed for safety and little cooling
is available. Using the right rated components (like X-class caps) is very important in preventing
risk of fire.A single resistor across the mains is a bad idea as if it fails an arc could envelop it and cause huge
fault currents - having several components in series limits the chance of heavy arc unless something
like lightning is involvedThe datasheet for a fusible resistor should explain the circumstances under which it fails (open) without
causing a fire. Typically 10x -- 30x overload or so. For instance http://www.farnell.com/datasheets/2045763.pdf
Dang, Excellent idea! I should have thought of that -- it's not like I haven't designed, and built, such things!
So, here's a capture of these ideas:
Be sure to configure the Data Pin, that you connect to the Opto, as INPUT_PULLUP!
Thank you to MarkT for catching the pointless 4k7 pull-up to +5V in my previous diagram. As he pointed out, by using the internal Arduino pull-up (20k to 50k), the Opto's internal LED can be driven at much lower current, and thus C1 and R1 get smaller (and probably less expensive)!
And, because the diagram in my original previous post presents a possible fire hazard -- I removed it!
Capacitive droppers are a clever way to power a small low voltage circuit like this from the mains in a small volume, where isolation of the supply isn't required. Its not obvious indeed, as mains is very low frequency
for a capacitive circuit, but the high voltages make up for this and the capacitance values aren't impractical.
You want to read electric appliance state.
Can you elaborate on that in some meaningful way? People are answering without knowing what it is exactly you want to do or think you want to do.