FAN (220V AC) Speed control

can any one provide me the zero crossing detector circuit...plz..?

AC Fan speed is control by a triac + diac + a VARIABLE Resistor that actually (with the help oa small cap) trigger the gate of Tric at various delay (according to the vale of variable RESISTOR) due to that delay tric get ON for that much time only.U break that variable resistor into= three fix resistor and switch them in to series with the help of transistor that will be control by your logic state. for example....if fan speed is controll fromm full to minimum by 500k resistor= use four 150k fix resistor in series = 600k and across each 150k resistor use (in parallel) a transistor or a opto when a transistor is switched on then 150k resistor is reduce to ~1k and 600k will be reduce to 450k and fan speed will increase...try and inform

PS: normally "NO"zero crossing detector required...only required for very precise design

You may damage your device if you do not have zero cross detector, as improper firing of triac might cause issue in the operating device.