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Author Topic: Reading input from A/V Receiver Audio speaker level output  (Read 809 times)
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Hello all!

I'm wondering how/if it's possible to route the speaker-level output of my A/V receiver through my Arduino Due, then transmit that data via a wireless signal - xbee, nordic, whatever - to another Due, then into the input of another amplifier.. sort of a poor-man's wireless audio network. I'm not expecting super high quality output, but something listenable to would be nice. I suspect Xbee won't be fast enoug.. but I do have a pair of DORJI Transceivers sitting here looking for a project.. (http://www.dorji.com/pro/RF-module/Medium_power_tranceiver.html - I've got the DRF4432D20I ones) I also have a pair of the raw RF modules too..

My A/V receiver outputs 90W per channel @ 8Ohm (125W @ 6 Ohms).

If I understand Ohms Law well enough for this application (Volts = Square Root of Power * Resistance).. so @ 90W, I'm playing with about 27 volts or so.. and I'd need to get that down into the range the Due can sample.

But I'm stuck on how I'd actually DO that. I'd thought about a simple voltage divider network, but I'm not quite sure how I'd match impedance so that I won't burn up my amp, or my due!

Anyone have any suggestions?
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Xbee sends data in packets not continuously so trying to stream audio data is tricky. It involves time stamping the data and un packing it at the other end and serialising it again.

It is not the easiest of projects to do.

The output of your a/v device is not 80 ohms, that is the impedance it can drive into. So that calculation does not make sense unless you terminate the output with an 80 R resistor, even then I am not so sure.
The total resistance in the potential divider should be 80R then work out the ratio. However the audio signal goes each side of ground so you need to increase the bias voltage to take it into the middle.
Maybe the best bet would be with an op amp, but you have some circuit design to do.
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Would something as simple as the following work (Pulled this right from http://www.epanorama.net/circuits/speaker_to_line.html) - the Due's input voltage is 3.3V max, which just "above" standard "Line Level" for audio devices @ 2.192V Peak (See: http://en.wikipedia.org/wiki/Line_level)

Code:
Speaker Out +  -----------
                           |
                           R1 @ 33KOhm
                           |
                           |--------------------------- Line OUT
                           |
                           R2 @ 1KOhm
                           |
                           |------------------------- Line GND
                           |
Speaker GND -------------

The DUE's input caps @ 3.3V.. Though now that I think about it...I'd still wind up with negative voltages here, right? Effectively a 0 reading on the Due.. I think you're right, and an OpAmp probably is the way to go. If you can't tell, I have no idea what I'm doing. smiley Guess I'm going to get to learn quite a bit this week as I figure this all out. smiley

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Effectively a 0 reading on the Due.

Yes and damaging it as well.

You can't get any great power out of a line level signal as defined in that page, so I suspect that is not what you have.
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Effectively a 0 reading on the Due.

Yes and damaging it as well.

You can't get any great power out of a line level signal as defined in that page, so I suspect that is not what you have.

No, Im aware. I have speaker level output on my A/V receiver, not line level. I was wondering if I could just use a divider and bring the voltages down with the diagram above, which is a simple speaker level to line-level circuit I'd found. But I'd still wind up with negative voltage, and so that's probably not going to work.
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But I'd still wind up with negative voltage, and so that's probably not going to work.
Correct.
So have 1K resistors from your analogue input to ground and +5V, then couple in the voltage from that divider to the analogue input using a capacitor.
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