I'd like to connect the audio output from a set-top box (and similar) to a microcontroller's ADC. They all have an RCA connector so I was wondering what sort of circuit may be required to interface the RCA audio output to the ADC on a microcontroller?
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\$\begingroup\$ Yes ,I only want to take audio directly from Set-top box via microcontroller. \$\endgroup\$ – Jignesh Patel Apr 21 '14 at 12:23
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\$\begingroup\$ @user40646, I've removed the confusing RF part and narrowed it down to just the hardware aspect. If this question is re-opened and answered how to take the samples on a particular microcontroller would be best as a new question if you run into any problems on that side (give it a go yourself first though). \$\endgroup\$ – PeterJ Apr 21 '14 at 13:09
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\$\begingroup\$ There are tons of off the shelf solutions to this problem. Why reinvent the wheel? \$\endgroup\$ – Matt Young Apr 21 '14 at 14:16
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Here is something to try:
Audio signals meant to go between equipment but not directly from microphones or meant to drive a speaker are usually at line level, which is usually around 1 V RMS. That is about the right amplitude for driving a microcontroller A/D input, but the DC level needs to be set close to half of the A/D range. This is what R2 and R3 do in this circuit.
C1 decouples the DC level of the input signal from that at the A/D input. R1 provides a little optional attenuation in case the audio level is too high and ends up clipping against the A/D limit too often.
Note that R2 and R3 together provide 50 kΩ of impedance as seen by the A/D input. The high pass filter formed by C1 and this impedance has a rolloff of 16 Hz, which is low enough to pass "HiFi" audio acceptably.
