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ADC for USB streaming AM radio audio
ADC for USB streaming AM radio audio
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Old 23rd April 2011, 03:39 AM   #1
elctrolaw is offline elctrolaw
diyAudio Member
Join Date: Apr 2011
Default ADC for USB streaming AM radio audio


Please forgive my questions as I am still trying to learn how to program for my project.

I'm trying to use a PIC18F2550 to stream AM radio quality analog audio (single channel) through the USB to be played out of the PC's speakers.

So far, I don't think I have the right settings because I have not been able to get any thing resembling audio out of the PC's speakers.

I have studied the 18F2550 data sheet and still have not been able to figure out the following:

1. I'm using a 24Mhz crystal on the PIC with the clock running at 48Mhz. How should ADC conversion speed be set? Right now it is FRC. Other choices would be FOSC/2, FOSC/8, FOSC/32, FOSC/4, FOSCc/16, FOSC/64.

2. What should acquisition time be? 40 program cycles?

3. I'm familiar with the Shannon-Nyquist theorem whereby you have to sample at twice the frequency, so I assume for AM radio quality, the sample rate would need to be around 41Khz?

4. I have tried to play the audio by using Audacity, VLC and several other programs, but have not been able to hear any audio. Is there another program that I should try that would be able to tell me if the audio is coming over the USB bus and is being converted back to analog by the DAC?

5. I have considered changing my design to just use a TI PCM2906B with the radio output going into the analog input of the chip and then over the USB bus to the PC. However, I also need to be able to change the tuning frequency of the radio I don't think the PCM2906B would allow any other commands except volume and moot through HID. Any comments on this idea?

Thanks so much for any comments or ideas.

Thanks in advance if anyone could help me.
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