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Topic: Two way data over audio (Read 948 times) previous topic - next topic


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?
Food for thought.


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.


Sep 18, 2012, 07:55 am Last Edit: Sep 18, 2012, 09:10 am by MattiasOfTheMetal Reason: 1
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.

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..
Food for thought.

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