PIC Audio

[sougata]

Hi,

If you use an 8 MHz crystal as your oscillator and let your timer0 run free it would interrupt @ 7.8Khz (Thanks to MisterE for the PIC multicalc utility). Enable timer0 interrupt. In the interrupt routine you don't need to reload timer0 as it already rolls over. This assures a solid timebase interrupting at fixed intervals. On the interrupt set the Go/Done bit of your ADC. Use the ADC in 8 bit mode. When the conversion is done. Simply dump the ADRESH value to the PWM duty register. All this happens in the interrupt routine. Let the AD module run continuosly so that sampling (acquisition) actually occurs when you are outside the interrupt. This should be quite simple to achieve. You get enough time outside the ISR to decide whether the ADC is sampling 0 or say 127 (when you are DC offsetting the Audio that gives you a 0 for the most negative peak, and 255 for most positive sort of pseudo signed ADC you loose resolution again, distort more).

[toofastdave]

Hi,

If you use an 8 MHz crystal as your oscillator and let your timer0 run free it would interrupt @ 7.8Khz (Thanks to MisterE for the PIC multicalc utility). Enable timer0 interrupt. In the interrupt routine you don't need to reload timer0 as it already rolls over. This assures a solid timebase interrupting at fixed intervals. On the interrupt set the Go/Done bit of your ADC. Use the ADC in 8 bit mode. When the conversion is done. Simply dump the ADRESH value to the PWM duty register. All this happens in the interrupt routine. Let the AD module run continuosly so that sampling (acquisition) actually occurs when you are outside the interrupt. This should be quite simple to achieve. You get enough time outside the ISR to decide whether the ADC is sampling 0 or say 127 (when you are DC offsetting the Audio that gives you a 0 for the most negative peak, and 255 for most positive sort of pseudo signed ADC you loose resolution again, distort more).

I'll have to look into this..it sounds interesting but it may keep my PIC busy for longer than I'd want it to be at any given time, especially if I have to monitor the start and end of the audio to communicate via SPI to another device. I'll play around with it though... Thanks for the great suggestion!

[toofastdave]

Hi,

If you use an 8 MHz crystal as your oscillator and let your timer0 run free it would interrupt @ 7.8Khz (Thanks to MisterE for the PIC multicalc utility). Enable timer0 interrupt. In the interrupt routine you don't need to reload timer0 as it already rolls over. This assures a solid timebase interrupting at fixed intervals. On the interrupt set the Go/Done bit of your ADC. Use the ADC in 8 bit mode. When the conversion is done. Simply dump the ADRESH value to the PWM duty register. All this happens in the interrupt routine. Let the AD module run continuosly so that sampling (acquisition) actually occurs when you are outside the interrupt. This should be quite simple to achieve. You get enough time outside the ISR to decide whether the ADC is sampling 0 or say 127 (when you are DC offsetting the Audio that gives you a 0 for the most negative peak, and 255 for most positive sort of pseudo signed ADC you loose resolution again, distort more).

sougata,
Do you have any example code of this application? It sounds like something I would like to try but ASM interrupts are over my head...I haven't gotten the whole interrupt concept down just yet...I'd appreciate anything you had to share to help me understand this idea.

Thanks!
Dave

[Sean_Goddard]

Try a precision full wave rectifier feeding a comparator with a reference set by a pot. This will give a logic level output you can poll using the PIC. When it's high, enable the amplifier, when it falls low activate your white noise burst. Try generating random numbers (8 bit) and feeding them to a 2R2 DAC, you could even just switch a diode noise source output into the amp input.

I did somethineg VERY similar for a company as a water leak detector. A microphone listened for a noise in the pipes then activated an alarm if the noise was of a certain type and exceeded a certain duration.

Hope this helps