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Author Topic: Two way data over audio  (Read 918 times)
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Monterey, CA
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Hi, my scenario is that I have an arduino onboard a guitar, and one inside my pedalboard. My goal is that I want them to communicate, but keep the standard mono 1/4 cable, and not have to use a special cable. I have the arduino powered by 9v, through "phantom power", which is a dc 9v signal carried from the pedalboard to the guitar over the regular cable (that part is complete).

I have a few ideas how to make them communicate, while sharing the same wire as an audio signal and a dc power signal.
I was considering fm transmission with the nrf24 chip. I wish for 2 way communication, if possible, without interference between the audio/power and the data communication. So far the only idea I have is to use an rf filter, and to seperate the frequencies buy a lot; guitar freq. is around 5khz, and if I used a 315mhz from the guitar -> pedalboard, and a 433mhz from pedalboard -> guitar, with a filter inbetween the data freq. and audio freq. Also, I have read that a modem IC would work well, but I have no idea how to go about that.

Does anyone have any insight on this, or has had experience with anything similar?
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Food for thought.
Nom.

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It sounds like it should be possible, but I've never done anything like that.

To me, it sounds like lots of work just to use a standard guitar cable when there's nothing standard on either end of the guitar cable...   

Standard phantom power for a studio microphone is sent common-mode over a differential (3-wire) connection, so that a standard dynamic microphone never "sees" the voltage across it's coil.    9VDC accidently plugged-into a standard guitar pickup, or into a standard amp or pedal probably won't damage it, but it might be better to play it safe and use a different connector. 

And if you are going to use FM transmission, I'd stick a battery in the guitar and go totally wireless.
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Thanks for your input, I was considering doing it pure wireless, definitely would be more convenient. The only issue, is that on the guitar I have a few rgb led strips that are under the fretboard, that will draw around 2 amps at peak(Its a white vine inlay, and I've routed out the back of the fretboard).
So onboard power will be a matter all its own, and I don't want to have 6-12 d batteries. And a few Giant capacitors, while more doable, wasn't what I had in mind.

The other thing with wireless, I would have to do considerable work to get an adc chip to the rf chip, then vice versa on the receiving end, while transmitting serial data. The nrf2401's datasheet (http://pdf1.alldatasheet.com/datasheet-pdf/view/90046/ETC/NRF2401.html) states on the first page that it is multi channel capable, up to 125 total channels. Could I use a few channels for serial communication, and a few for simultaneous audio transfer? I don't want to pick up and interference while playing live with this rig, which is why I figured a 1/4 cable wouldn't pick up any (shielded), and would be easily replaceable after the cable finally loses connection, rather than doing a custom cable and have to rebuild it every so often. I also didn't want a roadie to plug a wrong cable in to it by mistake, and mess it up. So I figured either wireless, standard cable (idiot proof), or an easy to come by, but more rare for audio applications cable.

On a side note, is there a more efficient way to transmit audio wirelessly without converting to digital at all? I figure air is not much different to a copper wire in the case of audio.

EDIT:
The nRF2460 seems to be a good candidate.
"The nRF2460's 4Mbps bandwidth also provides ample space to support an auxiliary wireless data channel for user control functions such as mute and volume up/down." (http://www.nordicsemi.com/News/Press-Releases/Product-Related-News/New-Nordic-nRF2460-audio-streamer-IC-delivers-unique-class-leading-cost-and-power-optimization-for-mono-wireless-audio-applications)

Any chance of sending simple serial data between the guitar and pedalboard?
It says the chip has a bandwidth of 4mbps, I figured the serial data will be simple; the pedalboard will tell the guitar's arduino to change 4 digital pots, and 3 dpdt relays, and will override the color on demand(the leds will change color depending on its mode that is set from the pedalboard, and when requested will change to a constant update mode[I plan to incorporate a wah pedal; when active, it will fade between red@toe down, and blue@heeldown]).
I think that may end up to < 0.1 of the 4mbps.

My question lies at:
1: Is there a more efficient way to do this?
2. It is a 36 pin QFN package, how do I go about converting this to a DIP or atleast pcb mountable? From my searching the cheapest board I could find was 20 dollars! The chip is only 5 dollars on mouser..
« Last Edit: September 18, 2012, 02:10:57 am by MattiasOfTheMetal » Logged

Food for thought.
Nom.

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