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Author Topic: NRF24L01+ antenna connected to AC audio line  (Read 938 times)
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Monterey, CA
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Hi,

First, I have a few of these:
http://www.exp-tech.de/images/product_images/original_images/b9e551faebe0bf1227bc08d1b19f285e.image.550x550.jpg

http://www.emartee.com/Images/websites/emartee.com/RF24013.jpg

My question, is I plan to put one of these in my guitar, and one in my pedalboard. So the voltage will be +/- 1VAC.
Will there be an issue with having the antenna directly attached to either of the AC wires?
Meaning, will an AC voltage that low mess up the NRF24L01+?

I have considered using diodes to prevent flow to the antenna, but wouldn't that make it so neither chip could listen, only speak?

I think the audio signal would be fine, considering the nordic chip communicates at 2.4 ghz and would be far out of the range of human hearing. I will also put a filter for above 1ghz to save my pedalboard and amp.

Thanks!
-Matt
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Food for thought.
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UK
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You've totally lost me. Why would you connect the antenna of the module to anything, let alone an AC signal?

I don't understand what you are trying to do here.
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North Queensland, Australia
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If you are trying to feed the wireless signal into the guitar signal, I'd imagine the amp or whatever you plug it into would have a band pass/low pass filter which will kill the 2.4 GHz signal. But you said you are adding that in, I'm pretty lost too. Is the guitar cable, or strings supposed to become an antenna?
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Anaheim CA.
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Maybe OP thinks a nRF24XX will handle audio..

Bob

In real time...
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Monterey, CA
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EDIT:

I understand the NRF24 does not transmit an analog signal. A DAC/ADC combo would be necessary for that.

The attached picture shows the diagram.

In the future I plan to make a 2-way wireless guitar adapter. 2-way is necessary for guitar's and pedalboard's arduinos to communicate, while still passing the analog signal.
This would need to be backwards compatible with a regular guitar cable, and work on any guitar.

My idea for the wireless guitar thingy: (any)guitar->ADC->NRF24->air->NRF24->DAC->amp/pedals/whatever.
So with the NRF equipped guitars, it would be: arduino-->nrf24->(in parallel with guitar signal)->guitar cable->pedalboard->(splits to nrf24->arduino and guitar signal->pedals).
In this case, with the 'wireless guitar thingy', I could directly swap out the guitar cable with it.

I cannot have the nrf24's go through the air, it must be through the guitar cable. (will have no interference if I turn and am between the two nrf24s, physical objects in between the two will not affect performance, better asthetics, not having a 4 inch antenna sticking out of my guitar and having 2 of them when I go full wireless, etc.)
Overall, its better for it to be hidden and operate on a specific line, rather than the airwaves.

Does this make sense?
If the signal goes through the guitar cable, there will not be anything in the way of the transmitted signal, and there won't be outside interference due to the cable's shielding.

Sorry for the confusion.

So, my main question: will a very very low voltage AC signal hurt the nrf24s? I would assume not, since it is well below its operating voltage (even if its AC).

-Matt


* Arduino example guitar.png (33.13 KB, 1055x331 - viewed 31 times.)
« Last Edit: January 31, 2013, 11:49:31 pm by MattiasOfTheMetal » Logged

Food for thought.
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NRF's are wireless devices. They are designed to transmit RF.

If you don't want wireless then why are you even talking about using wireless transceivers?
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Manchester (England England)
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Quote
Does this make sense?
No.
Quote
I cannot have the nrf24's go through the air,
Why not that is what it is designed to do.
Quote
it must be through the guitar cable. (will have no interference if I turn and am between the two nrf24s,
If you want it to go through a cable then you have the wrong device your transmitter will not work like this at all. You need a modulation device some what like that used for communications through the mains.

Quote
not having a 4 inch antenna sticking out of my guitar
Why, that picture you posted showed it had a PCB antenna, why do ypu want another one?

Quote
So, my main question: will a very very low voltage AC signal hurt the nrf24s?
Yes it will.
Quote
I would assume not, since it is well below its operating voltage (even if its AC).
There are more ways of damaging an input than taking it over the supply voltage. A 1V signal is massive compared to the signal it is designed to amplify, it would not surprise me if it blew the front end.

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Monterey, CA
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Mike, thank you for answering my question.

Do you know of a better module than to use the NRF24 in this circuit?

I basically wanted a >1ghz fm communication line that wasn't going to cost me an arm and a leg, would work for a good distance(the farther the better), and would work over the guitar cable rather than through the air.
I was only thinking to use the NRF's because I have a few of them lying around, and they are really cheap in price, good distance, etc.

-Matt
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I basically wanted a >1ghz fm communication line ............. and would work over the guitar cable rather than through the air.
Those requirements are mutually exclusive. A guitar cable can not carry a 1GHz signal. It is a shielded cable, and the capacitance of the cable will kill a 1GHz signal stone dead.

If you do want to do this trick then modulating the information at something like 500KHz is what you need to do. However I don't know of anything that does this sort of thing apart from the mains ( AC power or line depending on where you live ) controllers that turn stuff on and off by sending signals through the domestic wiring.
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The issue with antenna size depends on the RF band used.  The issue with cross talk means choosing suitable correct
channels to avoid interference.  The issue with signal dropping out is why you want antenna diversity (2 or more
receiver antennas at difference positions/angles - which with the Nordic module means having more than one
listening.

An RF antenna is a tuned component - place it near some other metal and its efficiency can drop by large factors.
To be honest the PCB antennas on that module are not great - get a module which takes a plug-in antenna and use
a 1/4 wave whip (not very big at 2.4GHz)

There are ways of coupling an antenna to a wire to cause the signal to travel along the wire, but its really not going
to work here as the wire will re-radiate the signal within a few wavelengths anyway (if unshielded), or probably be
mainly absorbed (in a shielded audio cable which don't use suitable insulation for UHF) - and the coupling has to
be tuned for the RF carrier frequency for any efficiency.

Or the far simpler solution:  Add another wire to run alongside the audio cable and carry the data.  CAT5 perhaps?
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Monterey, CA
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Thanks for the input.

I considered running another cable alongside the guitar's cable, which would be easily doable. However, if said cable ever crapped out while playing live, the most common cable on hand is a mono 1/4 cable. I suppose building my own cable would be the simplest.

I could do the fm thing, as long as its above 20khz honestly. 2.4ghz was just more readily available.
Given the circumstance (guitar cables defeat 1+ ghz), if I used a stereo guitar cable, I could have power over the cable instead of only onboard battery power, but could I use that as a two way communication line as well? For instance, on the left channel (tip) would be audio, on the right channel (ring) would be power to the arduino, and communication to and from the pedalboard.

As long as it wouldn't be heard or interfere with the audio signal, would provide reliable power and communication, would this be doable without building a proprietary cable?
It would be nice to be backwards compatible with a regular mono 1/4" cable when I choose to play it like a regular guitar, so I would be limited to using a 1/4" mono or stereo.
Also, I am going for a sleek look on the guitar, so having multiple ports for different scenarios is not my preference.

-Matt
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Food for thought.
Nom.

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