I am able to control the brightness of an LED with a pot and the output via PWM pin..
In the similar way how do I control the speed of a AC 220v fan or light ..??
There should me no humming in the fan
In the similar way how do I control the speed of a AC 220v fan or light ..??
That cannot happen with AC light dimming you have to slice at the right time depending on the frequency and voltage to lower the voltage so as to dim, PWM;s won;t work with AC lighting.
yes I know that it is not possible directly..
So what other parts should I use to do That..
Like in this schematic here
How do I control the R1 with arduino...??
yes I know that it is not possible directly..
It's not the question of directly or indirectly it's basically because you need to ascertain the Zero Crossing and as per that you have to open the traic for that time only that will give you desired dimming.
@NI$HANT
You forgot to tell Joy your tread. 
@Joy
Check this tread. http://arduino.cc/forum/index.php/topic,91274.0.html
I did a schematic and a code to control AC using an Arduino. It is just for a 12 V AC for now ( I am working on it for the 120 V AV version )
You forgot to tell Joy your tread.
First wanted him to learn that why we are telling him what we are telling him?, just wanted to make him work his way out of that previous concept of PWM'ing the A/C line's.
then how do those remote for home lights and fans control the fan speed...??
Go to the link above provided, also learn of zero crossing , google it and then learn how to slice the voltage by using it.
Just found this schematic
it is using an opto coupler and a opto triac driver..
But theoretically how is it controlling the fan speed...??
by switching on and of the fan a number of times and varying that time..??
First, you need to know how a dimmer switch work so you can understand the principle how to control an AC voltage.
Here a link : How Dimmer Switches Work | HowStuffWorks
And go to NI$HANT tread. My design use this principle. Bear in mind it is only one device being control. To control multitude devices is no so easy for me at this time. It is going to be "tricky". It is the sychronization is going to be "tricky" part to control different AC devices at differents "dim" levels.
Thanks for the howstuffworks link! This explains it all!
Ya but then it helps!
Microchip´s Application Notes could help you
hi nishant joy n everyone arduino is kind of new to me 
i know just a little bit about it. i want to control my. ac fan. ohhh i live in India 220 volt 50 hz
i want to control its speed. >:( i have seen n read all the posts but i havent understood any of it. plz plz tell me what hardware and. what hardware device i have to learn about. plz nishant help me. any adive would be highly appriciated. 
The simple advice is you can't. Standard induction motors in domestic appliances cannot
safely be speed-controlled (some can be a little, but its not easy to find out by how much).
Get a DC fan.
Hello All,
This thread has been very useful. I am not sure about one thing - for a 110vAC fan control circuit do I need to use the transformer to get 12V-0V-12V or is there a way I can use the AC supply directly into the optocoupler to drive the MCU. I believe I saw a schematic snap shot which shows AC supply connected directly to OC and then OC talking to the MCU.
Thanks.
there is a simple way to do this.you want some 3 triacs(for 3 speed fan)and hack the speed regulator of the fan.and use digital outputs from arduino to switch triacs.
amsaiyed:
Hello All,This thread has been very useful. I am not sure about one thing - for a 110vAC fan control circuit do I need to use the transformer to get 12V-0V-12V or is there a way I can use the AC supply directly into the optocoupler to drive the MCU. I believe I saw a schematic snap shot which shows AC supply connected directly to OC and then OC talking to the MCU.
Thanks.
Hi,
I dont know how much you already know about triggering a triac for dimming or speed control so i'll outline it here.
In order to get away without a transformer, you can use half wave rectification to create the DC supply for the circuit. That way you can 'ground' one side of the AC.
Note that this can be dangerous. The pot you use for adjustment should have a plastic shaft not metal so it cant conduct to the hands.
The triac works the same in each half cycle of the line voltage, just with opposite polarity. The circuit senses the zero cross of the line, then waits a predetermined time, then sends a pulse to the triac gate to turn it on. So the load only sees part of each half cycle rather than the full half cycle for each half cycle and that is what 'dims' the load.
The predetermined time is set by the user by turning the shaft of the pot, and the circuit detects how many degrees the shaft has been turned and changes the predetermined time delay as required. The delay can be anything from close to zero to a little less than one half cycle time. If the delay is close to the half cycle time then the triac never turn on, so that would be for max dimming.
Some dimmer switches you buy at the store work with fans. Maybe all modern dimmers work with fans but i havent tested them all.
Please note that this kind of circuit can be dangerous because part of the circuit is connected directly to one side of the line voltage. Two prong plugs are often plugged in backwards, and sometimes the outlet is not wired right either so you cant depend on using the neutral lead of the line wire because it might become live for numerous reasons.
ok, Make something clear. RPM of AC motor are determine by: 120*f/pole.
So a 4 pole motor that are connected to 60Hz power line (america)= 120*60/4 =1800RPM.
So AC drive doesn't use duty cycle to manage speed, the change the frequency.
aside of creating a lot of harmonics, playing with duty cycle on AC motor can be hazardous for power line because, when powering up, an ac motor can pump until 6 time is nominal current. So switch on and of could be bad.
Hi,
Yes but what is strange is i have seen people do this and it does vary the speed and works for quite some time. Motors with brushes do work better as far as i know like with power tools.
Good AC drives change the voltage AND the frequency.
I use a DC fan for low speed myself.