FM transmitter using Arduino

Hi all,

I have a random idea,Its like coding a FM transmitters into an arduino board.

first step is to generate a sine wave with a frequency in FM band.
Then inputting an audio signal to the arduino board using analogRead() .
Now defining the frequency of the sine wave generated as a function of the amplitude of the inputted audio.

The FM output is then passed through a suitable RF power amplifier.
I hope this is a working Idea.

Please tell me your suggestions.
Thanks in advance.

myfaithnka:
I hope this is a working Idea.

Not until you can figure out how to get an Arduino to output an ~88-108 MHz signal (you know, the FM radio frequency band), using only a 16 MHz clock rate...

Now - you could generate an FM (ie, frequency modulated) signal the way you are proposing, it just wouldn't be in the band of FM radio. With AM radio, on the other hand, you stand a better chance. But I think you're going to need to brush up on your RF skills (and start researching on getting your ham license via the ARRL), before you go any further, unless you want big brother beating down your door (depending on how much interference you set up with experiments - maybe if you kept things low-key with no amplifier, you could keep things "inside your house").

cr0sh:

myfaithnka:
I hope this is a working Idea.

Not until you can figure out how to get an Arduino to output an ~88-108 MHz signal (you know, the FM radio frequency band), using only a 16 MHz clock rate...

Now - you could generate an FM (ie, frequency modulated) signal the way you are proposing, it just wouldn't be in the band of FM radio. With AM radio, on the other hand, you stand a better chance. But I think you're going to need to brush up on your RF skills (and start researching on getting your ham license via the ARRL), before you go any further, unless you want big brother beating down your door (depending on how much interference you set up with experiments - maybe if you kept things low-key with no amplifier, you could keep things "inside your house").

I've seen an FM/AM/SW/LW tuner board on sparkfun I was thinking about getting. Alas, it doesn't transmit, but that's not quite necessary anyways. But how can it read the FM without a 1:x frequency ratio?

At my old house, with one of the old radioshack SW/AM radio kits, I taped the wire antenna to our 20 ft flag pole, I was getting stuff in languages I didn't even have a clue how to comprehend. LOL

IMO, Big Brother is too busy with other stuff, than to carry an FM Vu meter around looking for unregistered activity..just saying.

But how can it read the FM without a 1:x frequency ratio?

In data sheet for Si4735: Freq synthesizer with integrated VCO.

Altogether with build-in DSP it's doing the hardest part, demodulation FM / AM and DM.
Probably arduino can work with FM around ~1 Mhz, but UP/DOWN freq. converters would be necessary to push it up to 88 MHz . Heterodyne front end, in other words.

hello everyone,

Well I was too bothered about the frequency range.

I was hoping for two solutions.

  • Use of a clock division.
    Use of boards like Pinguino.

I think here Big brother allows me for academic purposes and at low power.
Please continue to give me suggestions.

Your question was about FM transmitter. But then are you referring to FM receiver (from sparkfun).
Confusing.

You can use a heterodyne converter, the arduino can synth a 75Khz deviated carrier at 455KHz which is mixed with a crystal osc at the desired broadcast rate+455Khz. Remotecontrol transmitters use a similar method, deviate an IF and upmix to the set channel freq. Keep your ERP below 100mW please.

I think here Big brother allows me for academic purposes and at low power.

Where is "here", please fill in your location in your profile.

As others have said you can't use the arduino to directly generate the signals for an FM transmitter all you can do is use it to generate an FM carrier that you then have to apply to a mixer to get to the band you want.
What do you want to modulate, data or speech?

There are many modules and circuit designs out there for building FM modulators, these generate low power FM signal and take an audio input (some have built-in microphone). That then leaves the Arduino to do the audio processing - however it lacks a D->A converter which makes life harder - PWM is good for class D audio output but no use at all for driving an FM transmitter (without a decent multi-pole low-pass filter).

If not already searched for "software defined radio" do so!

Awesome project idea. Want is the application? Personal FM transmitter for audio? I think it would be double awesome if there could be RDS functionality too. Despite "big bother" in the US, there are still many many practical and legal applications of this. I may not be of much help, but will be watching as well :smiley:

I have stumbled upon several Gnu/Linux radio projects. But none that actually implement a modulator, they all use add-on hardware. I think MarkT is on to something.... you may need to find an AVR with a D/A or switch to something like a BeagleBoard. (You could still use Arduino with the AVR) One project that I cant find right now, actually used an RF modulator from old TVs and VCRs of an embedded LPFM station.

Its for GSM base stations and not FM, but there might be some ideas for you over at http://openbts.sourceforge.net/ (similar conceptual problems)

This FM transmitter does not use Arduino , but is a DYI mini transmitter for audio: http://www.openthing.org/products/niftymitter/

For the software defined radio approach you might want to check out a few in production already - the different from Arduinos. I see an Arduino USRP in shield, but not necessarily software defined radio implemented on only an AVR. Universal Software Radio Peripheral - Wikipedia

best of luck, tom

I don't advise the nifty mitter.... Single stage hartley oscillator in which the antenna is part of the feedback capacitive divider....Can we say allover the dial at once?

I found this old thread while doing some research. I thought I would post this link for others that may come across it as well.
FM transmitter using the Arduino: http://www.mikeyancey.com/FM-Stereo-Broadcaster.php

Oh come off it it is NOT FM transmission using an Arduino. It is just using an Arduino to control an FM transmitter. The Arduino takes no part in the signal generation or the modulation which is what the OP was talking about.
Use of this transmitter is still illegal in most places anyway.

Here is a three-component FM-band transmitter using an ATtiny45 as the oscillator and modulator. Plays music! Not Arduino, but a most impressive feat. With a range of a few inches, the FM Broadcast Police Force that is so worrisome to some people probably won't catch you.

Those people at hackaday are very easily impressed you can do a much better job with a transistor, but hey this uses a micro processor as an RC oscillator, remind me why this is not a crap idea.

the FM Broadcast Police Force that is so worrisome to some people probably won't catch you

So your attitude to legality is just governed by your chance of detection? Not the potential life threatening consequences of interfering with emergency services, life support systems and the rest. What a nice chap you are.

Grumpy_Mike:
So your attitude to legality is just governed by your chance of detection? Not the potential life threatening consequences of interfering with emergency services, life support systems and the rest. What a nice chap you are.

Which is what I was trying to get at in my original post; furthermore, "big brother" really meant the ton of HAM radio enthusiasts out there, who, if they detect such interference, etc - might decide to do a "fox hunt", find the source - and then they would alert the FCC (or whatever agency is in your area/country). The government doesn't need to drive around a van looking for violaters - they have a built up HAM operator network composed of many that don't like to see such interference from unlicensed operators.

Don't be silly, folks. In the U.S. such low power transmissions are expressly authorized, and I imagine that a similar situation holds true in many other countries. Specifically, the ATtiny45 transmitter would be a PART 15 FM device under the FCC rules: Low Power Radio - General Information | Federal Communications Commission

Unlicensed operation on the AM and FM radio broadcast bands is permitted for some extremely low powered devices covered under Part 15 of the FCC's rules. On FM frequencies, these devices are limited to an effective service range of approximately 200 feet (61 meters). See 47 CFR (Code of Federal Regulations) Section 15.239, and the July 24, 1991 Public Notice. On the AM broadcast band, these devices are limited to an effective service range of approximately 200 feet (61 meters). See 47 CFR Sections 15.207, 15.209, 15.219, and 15.221. These devices must accept any interference caused by any other operation, which may further limit the effective service range.

and I imagine that a similar situation holds true in many other countries

That is where you are wrong.

As I said, don't be silly. A very quick check reveals that unlicensed, low powered FM transmitters are also specifically authorized in Australia, New Zealand, Canada and Japan. Agreed, low powered FM-band transmitters do not appear to be allowed in The Netherlands or England, but I didn't bother to look much further. Of course, each hopeful experimenter should consult the regulations of his/her particular country.

Example: Australia:

Radiocommunications (Low Interference Potential Devices) Class Licence 2000
(1) This Class Licence authorises a person to operate a transmitter included in a class of transmitters mentioned in item in Schedule 1, subject to the following conditions:
(a) the transmitter must be operated:
(i) on a frequency, or within a range of frequencies, mentioned in
the item; and
(ii) at a radiated power that does not exceed the maximum EIRP
mentioned in the item; and
(iii) within the limitations (if any) mentioned in the item;
(b) the transmitter’s operation must not cause interference to the operation
of radiocommunications services.

Schedule 1 Transmitters
Item 21: Wireless audio transmitters and auditory assistance transmitters
Freq: 88-108 Mhz
Max EIRP: 10uW

Example: New Zealand:

New Zealand residents are allowed to broadcast licence free-of-charge at a maximum of 1 watt EIRP in the FM guardbands from 87.6 to 88.3 and from 106.7 to 107.7 MHz under a General User Radio License (GURL), which is issued by Radio Spectrum Management, managed by the Ministry of Economic Development.

Not impressed you pick two very sparkly populated countries.
It is not allowed in the whole of Europe, or Russia.
Note that all those regulations say they must not cause interference with others even if they comply to all the other regulations.
Also the range of frequencies is tight, which is impossible to control with the free running crap types of circuits lauded by stupid people in articals like those posted.