Audio Input and ouput for the propeller

[Kye]

Hey guys,

I can't seem to find any information on this online and I'm having a bit of a problem figuring it out myself.

I want to get the propeller chip to be able to output audio and input audio. My idea is that if I use operational amplfiers to integrate a pwm wave I can then create a nice DAC for sound generation. For audio input I plan to use a comparator with a sample and check circuit which simply generates a voltage using the audio output technique and then·uses the campator to check if the voltage generated is equal to the input, this is then done very fast to sample the input.

Now, addtionally the point of the operational amplfiers is to produce a level shifted signal for the PC audio. The problem is... I can't seem to find good reference material on what the the PC audio line level voltage is and how it swings. Additonally I'm not sure if a the 5V power supply on the prop proto board can power the operational amplfiers.

I'm not really good at using analog circuits. Help would be appreciated.

Thank you,

Oh, at the bottom are some quick sketches of the circuits.

There would be 3 analog output circuits and 1 comparator circuit. The first two analog output circuits would generate stereo audio and third would be used to drive the analog input for the comparator to sample the input signal.

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Nyamekye,

[Paul Baker]

Kye, Check out Chip Gracey's Microphone to Headhones object (http://obex.parallax.com/objects/57/) in the object exchange. It uses the Propeller Demo Board (http://www.parallax.com/Portals/0/Downloads/docs/prod/prop/PropDemoDschem.pdf) circuits, the input is an AC coupled electret microphone (could be adapted to a line in) and ADC input circuit and the output is a simple RC circuit that is amplified.

I think your circuits will cause too much distortion for the singal to be close to the original.

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Paul Baker (mailto:pbaker@parallax.com)

[Kye]

You do not understand, the analog input is actually the signal from from the propeller chip using pwm.

The idea is that the operational amplfiers integrate (like low pass) the pwm signal to generate a voltage which is then level shifted to the proper level.

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Nyamekye,