I want to control brightness of lights (230V) with the Arduino, and I know that relays will just switch the lights on/off. If you have the circuit or any idea about which transistor to use and how to use then please reply.

(Sorry for my English.)

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    \$\begingroup\$ The method (circuit) for dimming 230V lights depends on the type of lights. A transistor connected to an Arduino will not be enough and will likely be a lethal hazard. \$\endgroup\$ – RedGrittyBrick May 7 '14 at 10:29
  • \$\begingroup\$ I'll obviously not connect the transistor direct to the Arduino. Transistor will driven by circuit of other transistors. \$\endgroup\$ – Tanishq Jaiswal May 7 '14 at 10:39
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    \$\begingroup\$ What kind of lights? Incandescent, LED, CCFL? How powerfull it is, or you needed it to be? \$\endgroup\$ – zzz May 7 '14 at 11:02
  • \$\begingroup\$ I want to adjust brightness of CFL, Bulbs and also want to control the speed of ceiling fan. \$\endgroup\$ – Tanishq Jaiswal May 7 '14 at 14:58

Although being quite simple, this circuit is not for begginers. It is connected directly to mains! If not properly designed, dangerous voltages can reach your Arduino and PC.

You will need an optocoupler for proper isolation. Also you will not be using a transistor, you'll need a triac.

Check this schematic from wiki.dxarts.washington.edu

enter image description here

It is using MOC3020M which contains an optoisolator and triac driver.

Similar schematic can also be found on Arduino Playground.

Do not build a circuit without proper isolation!

Do not replace MOC3020 with other parts (optocoupler and transistor/diac) unless you know what you are doing!

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    \$\begingroup\$ You might want to edit this answer to say how well it works with a 230V Fluorescent light tube or with a 230V LED light. Incandescents are somewhat rare in the EU and maybe elsewhere too. \$\endgroup\$ – RedGrittyBrick May 7 '14 at 13:21
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    \$\begingroup\$ @TanishqJaiswal note that it doesn't work for CCFL. \$\endgroup\$ – Cornelius May 7 '14 at 15:52
  • \$\begingroup\$ Then can you give me a circuit diagram or link if I want to dim bulbs. \$\endgroup\$ – Tanishq Jaiswal May 7 '14 at 17:06
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    \$\begingroup\$ @TanishqJaiswal check this electronics.stackexchange.com/questions/68246/… \$\endgroup\$ – Cornelius May 7 '14 at 17:09

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