This is the second part of the Nexus documentation series. The first part documents the Basic Kit. This time, we investigate the Mixer Module. Eventually, all of this will end up in a single document.
The (optional) Mixer module is a daughter board that sits atop the Main Board (see Basic Kit). This module provides a simple, yet extensible and hackable mechanism for mixing (up to) 12 audio channels down to stereo. Each channel can be mixed to either left or right using the L/R selector configuration headers.
The diagram at the right shows the routing for each channel. The center pins connect to the buffered outputs of channels 1 through 12 via 10K summing resistors. The left and right pins connect to the summing junctions of a dual OpAmp (OPA2209 low noise precision operational amplifier). The mixer gain is -1.