Control FM/AM Radio Frequency with Arduino?

Hi,

I'm wondering about the feasibility and requesting some guidance in the pursuance of a project that will use Arduino to dictate the radio frequency of old boom boxes. I believe this shouldn't be too difficult but I'm a newbie with electronics and Arduino so I figured I'd ask first.

Basically, I'd like to bypass the potentiometer on the boom box and cycle through stations with the Arduino. I suspect it might just be a matter of replacing the potentiometers wires with those coming from Arduino, but any insight would be great. I'm using older boom boxes so they should all have analog tuners.

If you are confused, here's a video of someone doing exactly what I want to do, but with a digital tuner: http://vimeo.com/20932884

Does anyone have advice on how I would get started?

Thank you so much.

Best,

-LL

I think those potentiometers are actually variable capacitors....

Almost all boom-boxes use a variable capacitor connect to a knob. Your best bet might be to connect a hobby servo to the variable capacitor.

I'm not too well versed in the FM realm, but for AM, the demodulator circuits will typically use a parallel RC filter circuit in order to tune it. Most boomboxes will use a variable capacitor(as the other posters mentioned), however,you could swap out the resistor that it's connected to and change the frequency using the equation f=1/(RC), where f is the frequency that you're trying to tune to. Again, this is for AM, I'm not too sure how to do FM demodulation.

You can also purchase both digital potentiometers and digital variable capacitors, which would make interfacing with the Arduino much more simple.

Edit: I just went through some old notes and it's very possible they would have a parallel LC circuit to tune to the carrier frequency, leaving the RC circuit to filter out the carrier frequency and leave behind the modulating signal. You could still use the digital cap and swap that in for the tank circuit if you wanted to, but the initial filter could be a few different possibilities, so my guess is you'll have to get some filter theory in if you wanted to do it the way you initially proposed, I don't think it'd be too bad, but if you just want to knock it out, it'spossible the servo motor the other poster mentioned would work better.

I just went through some old notes and it's very possible they would have a parallel LC circuit to tune to the carrier frequency, leaving the RC circuit to filter out the carrier frequency and leave behind the modulating signal.

No.

The tuning knob changes the frequency of an oscillator which is then mixed with the incoming antenna signal to give an intermediate frequency or IF. Popular values of IF are 10MHz and 450KHz.

You would have to know what circuit you are dealing with before you could design an arduino replacement. Perhaps one of those signal generators injecting directly into the IF mixer would be the real answer. However getting a motor to move the knob is maybe the best bet.

Thank you all so much for your replies, I really appreciate it!

I think using a servo may not be able to do what I'm after as I'd ideally like to jump through stations at "random" or at least cycle up and down very quickly, giving the illusion of spontaneity.

Do you all think I may be a bit out of my element? My prior experience with Arduino and electronics was very simple, involving tons of "if" statements sending MIDI and LED data.

I suppose the next step would be to take about the boombox I have and see what's controlling the receiver.

Again,

Thank you.

You get one of the digital tuning receiver modules available on eBay and such (AM tuners are not available any more as best I know), use the Arduino to set the frequency, and you add it to the “boom box” in place of the present tuner with the four-gang variable capacitor. That is to say, the only modification to the present circuitry is to disconnect the audio feed to the selector switch from the present tuner and feed it from your new tuner instead.

I very much doubt a servo would have anywhere near the necessary accuracy and resolution to control a tuning capacitor, even if you could resolve the backlash problem.

I remember at the 2011 Maker Faire in New York that Sparkfun had an exhibit that included one hell of a lot of FM tuner modules tuned to each channel in the FM broadcast spectrum. Then they were scanning the channels. Look up the tuner module to see if thy still do it.

There used to be an FM radio designed for plugging into an expansion socket of a PC, I used that to controll the radio with an other computer of the Arduino class of processors, many years ago.

Hacking an existing module like this is probbly the best way to do it.

If you want to replace the tuner there are two FM modules you could use, the TEA5767 and the SI4703. Both tune on commands over the I2C bus.

Have a look at RDA5870M or TEA5767. They both work with arduino, are very small but would need interfacing to your boombox amp or use an external amp if connected to anything other than earphones. When I did tests with them one module type was superior to the other but I'm not sure which. I think it was the TEA5767 that was better as that is the only test code I kept but it could be the same code works on both and that is the first code written.

Thank you all for your incredibly helpful replies.

I’m going to go ahead and try one of these modules and see if I can get the effect I’m looking for. Ultimately, I’ll need 4 total boomboxes for an installation I’m planning for the final of an art class in three weeks. I may do something else as my final project as I don’t know how long it’ll take to get the modules and 3 more boomboxes.

Paul__B:
You get one of the digital tuning receiver modules available on eBay and such (AM tuners are not available any more as best I know), use the Arduino to set the frequency, and you add it to the “boom box” in place of the present tuner with the four-gang variable capacitor. That is to say, the only modification to the present circuitry is to disconnect the audio feed to the selector switch from the present tuner and feed it from your new tuner instead.

I very much doubt a servo would have anywhere near the necessary accuracy and resolution to control a tuning capacitor, even if you could resolve the backlash problem.

Paul,

Would the four-gang variable capacitor be something in the boombox itself, a part of the FM module, or something extra I would need to buy? Sorry I’m such a noob at electronics…more of a computer guy :p.

Thank you all again!!! What a great community.

Currently your tuner will use a ganged capacitor. The modules mentioned don't use one, they use a phased locked loop.