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Wireless Sound

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AtomSoft

Well-Known Member
Hey guys i have a mp3 player and was woundering if it would be wise to use something like:

MRF24J40MA

I want to send the audio from player to this and then send receive it on another. I know i need a pretty fast pic ie: 16bit - 32bit to handle it correct?

So my main question is can i use the above transceiver module and a fast pic to do it all?
 
The data rate will be limited by the module rated at 250kbs, and not by the type of PIC used. If you could do it with an 18f, and a hardware uart at that rate, then go ahead and try it with the modules. Otherwise save yourself the money.
 
Have never messed with mp3, so no recommendation there. But if you could make it work with the uart, there is a shot I would think. I have seen wireless speakers so it must be doable in some form or another.

Only slightly frustrated with the MRF24J40MA, because have not been able to get the slave/node2 to connect up with Microchips precompiled MIWI & P2P demos. Probably something stupid on my part, like trying to breadboard these things, don't know. The demos are based on the 18LF4620 and 24F, 32F 3V chips.
 

AtomSoft

Well-Known Member
cool ! i think the breadboard would not be a good idea but im going to try it too heh... i dont have no modules as of yet but i might order today. or tomorrow ...

Im not dealing with MP3 data. Im dealing with audio from a mp3 player. So ADC is needed but fast... then on the other side DAC...

Since i just want to turn the audio into digital data then send the data wireless to the other one and turn the digital data back to analog audio.
 

AtomSoft

Well-Known Member
so nice audio is about 128kbs (i think) so 250 should be a nice overkill to have :D since i have to do a ADC then send it out then repeat. I should be able to do it fast enough. There may be a small delay in music changing and stuff but heh it will be worth it :D
 

Nigel Goodwin

Super Moderator
Most Helpful Member
so nice audio is about 128kbs (i think) so 250 should be a nice overkill to have :D since i have to do a ADC then send it out then repeat. I should be able to do it fast enough. There may be a small delay in music changing and stuff but heh it will be worth it :D

128kps is MPEG compressed, not plain audio - half that for stereo, you're down to 64kps, which is only 6400 bytes per second. Assuming you're only using 8 bit data, that's about a 3KHz bandwidth - a very poor AM radio.

Do the maths!.
 

Mr RB

Well-Known Member
You can buy nice pre-made stereo FM transmitters made just for this purpose.

I know you said you didn't want to use an FM transmitter but it's looking better and better...
 

AtomSoft

Well-Known Member
Nigel and RB I just hate the noise that it has. Is it possible the ones i dealt with were too cheap and crap.

So if i build one you think it will be better? Any links to some?

Also nigel what kinda speed would i need to send stereo quality audio wireless?
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Nigel and RB I just hate the noise that it has. Is it possible the ones i dealt with were too cheap and crap.

The quality is normally excellent, were you trying to use them over too great a range?.

So if i build one you think it will be better? Any links to some?

Also nigel what kinda speed would i need to send stereo quality audio wireless?

CD quality is sampled at 44.1KHz and 16 bits per channel, so that's 1.76mbs, assuming 10 bit data bytes as per RS232.
 

Oznog

Active Member
And note that 1.764mb/sec is beyond the capabilities of the PIC18F to generate. The DSP chips, maybe not.

Now COMPRESSED data MP3/Ogg/whatever is far more practical. However, even the DSP chips have only limited ability to do the necessary math. There are many decompressor chips for MP3, but compressors are quite rare.

So, you can start with an MP3 file on flash card and beam that to a receiver with an MP3 decoder on board. That's straightforward. It's within the bandwidth of higher performance hardware like Bluetooth. But... starting with an analog input, you've got no straightforward way to compress the data with any useful quality.

I have noted abuse of the term "codec" chip for these compression formats. "codec" means "coder" AND "decoder". Most claiming to be codecs are in actuality decoders. Some have an ADC to encode incoming audio into uncompressed digital data, which may be a useful task to some, but it is NOT MP3/Ogg/etc encoding and it's misleading to term this an "Ogg codec" when it does not encode into Ogg.
 

Oznog

Active Member
heh i might just use some ARM mcu's. Im thinking of some cheap $5 LPC2103's to do that stuff for me
Well, you can look into it, but realtime decoding compressed audio is often beyond the capabilities of a microcontroller. Encoding often takes much more processing than decoding.
You'd think a big, powerful, advanced microcontroller could do that job if a much smaller ASIC could do it, but no it just doesn't work that way. This is one case where an ASIC can usually drive circles around the best of microcontrollers.
 
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