ggedamed

Re: Netduino onboard ADC for audio
« Reply #20 on: April 12, 2013, 06:55:38 AM »
Sorry, man, my cold is gone and my child is on holiday . So not much spare time from now on.

Take a look here.

First, you should keep a resistor between the cursor of P2 and the inverting input of the op amp (BTW, it would much easier to discuss if the op amps would have names), to limit the op amp gain at the ends of the pot travel.
Then replace P3 and R4 with 2 resistors, like this (figure 2):

Let's say Vo is the output voltage of the op amp. Vout from the page linked above would be Vo * R4 / (R3 + R4). Use it in the eqations in the page linked above and there you have it.

I leave it to you as an exercise the alternative blend control from figure 3.

Minds are like parachutes. They only function when they are open. (Sir James Dewar, Scientist, 1877-1925)

knutolai

Re: Netduino onboard ADC for audio
« Reply #21 on: April 12, 2013, 12:45:09 PM »
Quote
Vout from the page linked above would be Vo * R4 / (R3 + R4).

you mean Vin * R4 / (R3 + R4) right?

Quote
maximum gain is 10k / 47k * (10k (the pot) + 100) / 100 ~ 21.48.

This is where you lost me. I cant see how that calculation relates to that simple formula. 100 is the the 100R resistor R4 right (in my schematic)?