In SX Microcontrollers, SX/B Compiler and SX-Key Tool, g_daubach wrote:

Kevin,

in the schematic I have suggested, decoupling is done by the resistor in series with the audio signal, and not with the diode.

Using the comparator is pretty easy:

; Configuring the comparator
  mode $08  ; access CMP_B
  mov w, #%01000000
  mov !rb, w  ;enable comparator, do not enable comp. output at rb.0

; Insert a delay to allow comparator to respond

; Reading the comparator (same as above)
  mode $08  ; access CMP_B
  mov w, #%01000000
  mov !rb, w  ;enable comparator, do not enable comp. output at rb.0, and copy comp. result into w

; When bit 0 in w is set (w = 1), the voltage at rb.2 is greater than the voltage at rb.1

When you don't neet port pin rb.0 for other purposes, you could enable the comparator output (write %00000000 to !rb instead of %01000000). You then can directly check the state of rb.0 for the current comparator result, i.e. you don't need to execute the second

  mode $08  ; access CMP_B
  mov w, #%01000000
  mov !rb, w  ;enable comparator, do not enable comp. output at rb.0, and copy comp. result into w

in a loop for reading the result.

Assuming the potentiometer is set correctly, the comparator status would be 1 for no audio, and 0 for audio. You can always exchange the rb.1 and rb.2 pins if you like an inverted result, i.e. 1 for audio, and 0 for no audio.

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