In tympan Rev C schematic there are few resistors termed DIP (do not populate). I did my bit of research and understood where DNP is mentioned that portion of circuit is open. I’am still unclear regarding its significance.
Why is DNP resistor used?
Should those resistors be connected in circuit? If yes, how to arrive at resistor value?
As you found, DNP does indeed mean “do not populate”. These spaces in the circuit are left empty because we did want to make the connection by default. But, because the pads are there in the circuit, it enables others to easily modify their device if they so choose.
For example, as delivered, the Tympan will only provide a microphone bias voltage to one channel of an external microphone via the red microphone jack (ie, it’ll only be mono, not stereo). This was done on purpose. But, if you really want to use a stereo microphone via the red microphone jack, you can solder a 2.2K resistor into the empty space of R16, as described in the forum post below:
So, the DNP are to allow additional hacking of the hardware so that advanced users can further tailor the operation of the device to their liking.