I'm having a fine working Fm transmitter circuit in which i can transmit my speech up-to 3Km. I was wondering could i use my iphone's earphone jack's output as a signal input to the circuit so that i can transmit things through my FM transmitter.
Just gonna try with something like this before jumping to my expensive phone
Would be a silly stuff but it would be fun. 
Ok, so you have some illegal broadcasting equipment. Good for your (bad for the people who want to make legitimate use of the frequencies).
So what is your Arduino related question?
mattjackson:
I was wondering could i use my iphone's earphone jack's output as a signal input to the circuit so that i can transmit things through my FM transmitter.
Does your transmitter have a 3.5mm jack as input? If yes then you can.
Be careful long range FM frequency transmitters are only supposed to be used by licensed broadcasters but you can technically (NOT Legally) use very short range FM transmitters if their range doesn't exceed the limits of your house.
Edit:
Also you might already know this, use an unused frequency or your broadcast will interfere and disrupt with the existing FM channel and you get garble. You can kinda avoid this by living inside a Faraday cage.
use an unused frequency
Their are no unused frequencies in the FM band. If you find a channel where you can receive no signal that does not mean that the channel is unused. It means that if you transmit from that location their will be a place that can receive your signal AND the signal that is supposed to use that channel and thus you will cause interference.
but you can technically (NOT Legally) use very short range FM transmitters if their range doesn't exceed the limits of your house.
So you view of legality it that it dosn't matter what is legal as long as their is little chance of getting caught.
Finally that circuit the OP linked to is just a heap of crap. It is a free running oscillator and it will not be stable. The signal will wander all over the band and you have to continually re-tune the receiver. Also the language used in that web page hints at some one who has not got a clue about what he is doing.
a/ it's illegal.
b/ as GM says it's a lousy circuit.
c/ If you want a range of 3kM you'll need a great deal more power than that circuit will generate
Allan
I took the cable of a headpiece and took the 3 wires. Apparently i just gave the one signal and ground to the signal input in my circuit.
well it did not worked for some KMs as i thought but it was good enough to broadcast my iphone music to the neighbors, i tried cutting down the conductor to the half, and more half.
Guess what,
the range is just few meters now. Not even to my neighbor's house. Now i do not suppose that will make any legal offence, however i can manage to make something like a wireless home-theater or thing.
I'll try to shoot a video and surely gonna share link with you guys.
Till then a suggestion from you guys for making stereo sound transmission would be appreciable. Since in this circuit i could either use left ear signal or right ear signal.
!
I'm afraid your ignorance is beyond simple hints.
1/ Don't do it. The power required is at least 1000 times higher than the simple circuit you linked will generate and is totally illegal. And people would soon notice.
2/ Encoding stereo to be compatible with standard FM receivers isn't trivial either.
3/ for short range just buy a standard Bluetooth product.
Allan
mattjackson:
Now i do not suppose that will make any legal offence,
That is where you would be wrong. What country are you in? In Europe any transmission no matter how short is illegal.
Here in the US, before the do-it-all- smartphone /car stereo, they sold a low power transmitter that simply plugged into the audio jack of your phone and could be played over a FM station in your car. I had one. It was horrible.
Yes but those were "type approved". That means the transmitter design and construction had to have a certificate and have been tested. This is not a thing an individual could do due to the cost.
They were illegal in the UK until 2008.
Grumpy_Mike:
Their are no unused frequencies in the FM band. If you find a channel where you can receive no signal that does not mean that the channel is unused. It means that if you transmit from that location their will be a place that can receive your signal AND the signal that is supposed to use that channel and thus you will cause interference.
I was only advising the OP that if he wanted to get a clear reception from his transmitter then he has to use a free channel which his receiver cannot pick up any broadcast.
Grumpy_Mike:
So you view of legality it that it dosn't matter what is legal as long as their is little chance of getting caught.
Grumpy_Mike:
What country are you in? In Europe any transmission no matter how short is illegal.
Not anymore.
BBC - "The new Wireless Telegraphy (Exemption) (Amendment) Regulations 2006 mean that certain low-power transmitters will now be legal.
FirstPost - The new amendments will now apply to the European Union's standards on low-power transmitters. As long as they have the CE mark.
tinman13kup:
Here in the US, before the do-it-all- smartphone /car stereo, they sold a low power transmitter that simply plugged into the audio jack of your phone and could be played over a FM station in your car. I had one. It was horrible.
These FM transmitters are legal in the United States as long as they meet the FCC guidelines and carry the FCC declaration of conformity.
As I said that dose not mean you can build your own transmitter, that is still illegal in the UK.
Fair enough.
Edit: I recommend he should either buy a certified/approved product or apply for an FM broadcast license if building one himself. 
apply for an FM broadcast license if building one himself
He won't get one without an approved design and a compliance ceritificate to eg an ETSI spec (in Europe - FCC in the States) from a recognised test house -eg RFI in Basingstoke.
Done it quite a few times.
I wasn't paying - it isn't cheap.
His (paper) design has no chance of passing any specification because of it's inherent frequency instabilty, and probable high emission of harmonics, plus no means of limiting over-modulation causing adjacent channel interference. For a start.
Allan
A quote from the FCC, in the USA, made in the latest issue of ham radio magazine, CQ, is: "FCC rules permit unlicensed signals on the band (FM) who's signal does not exceed 250 microvolts per meter at 3 meters from the antenna". So, it's not any type approval or any other requirements other than transmitted power.
The ham in question was transmitting 176,526 microvolts on 90.9 MHz.
Paul
Didn't know the FCC permitted small untested unlicensed tx's - presumably only in certain bands. Not true in the UK. Even in the US wouldn't it be wise to have somebody measure the power before using it to avoid problems?
Presumably the ham got a slap - ham bands don't include FM broadcast!
I wouldn't quote a measurement like '176,526 microvolts on 90.9 MHz'. What does it mean?
Even with precision lab gear and calibrated cable connections we're suspicious of anything closer than +/- 0.5dB , never mind an open - air link with possible reflections etc. Anechoic chambers maybe a bit better.
I don't think the OP will get a 3km range with a transmitter that only gives 250uV/m at 3m.
Try the inverse square law - that'll be 10^6 times less...
Not much.
Allan
Didn't know the FCC permitted small untested unlicensed tx's
Yes they do as a sort of sop to "freedom of expression". However in practice the regulations are such that you need to know a hell of a lot in order to demonstrate you are within the limits.
This is the FCC document.
I like this bit:-
Furthermore, if the Commission determines that the operator of such a transmitter has not attempted to ensure compliance with the Part 15 technical standards by employing good engineering practices then that operator may be fined up to $10,000 for each violation and $75,000 for a repeat or continuing violation.
$10,000 ! So much for his Pirate Radio.
Who cares if its illegal? Just buy 1 transmitter, set a frequency, get 30+cm antenna, tell a friend to go a far far away, and test if there is signal. How would care for legality? Its EU here and I dont mean Germany of France or any big country 
Just do your fun.
All i recommend is to buy a more powerful FM transmitter. I doubt that little guy will perform well over distance as ther are many interruptions.
JMD1:
Who cares if its illegal?
Come on, it's not "big brother". The regulations are there to ensure that the valuable resource of the EM spectrum is protected from harmful interference and can be effectively used and shared.
Commercial FM licenses are carefully allocated by transmitter location, so as to minimize interference between stations using the same frequency, or close frequency. The only place where it actually doesn't matter much is in vast rural areas because there are so few stations due to the fact of barely beyond the horizon propogation.