From HwB

Cir OpAmpInvMany2.png

VOUT= -(V1/R1+V2/R2)*RO

This circuit is used to add several signals to one. By setting all resistors to the same value, R1=R2=RO, you get the following formula:

VOUT= -(V1+V2)

You can theoretically add how many signals you like. Here's an example with three in-signals:

Cir OpAmpInvMany.png

VOUT= -(V1/R1+V2/R2+V3/R3)*RO



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