Hi everyone, first post so go easy :) What I want to do is design a circuit to add two square wave frequencies into one output. The use is for a vehicle fitted with a Karman Vortex mass airflow sensor. The MAF sensor has a 5V square wave output of 0~150Hz. The vehicle has been modified with twin throttle bodies currently plumbed back to a single MAF. The idea is to run two MAF sensors, one for each throttle body. So how do I combine the two signals into one output to the ECU? The problem that I see is that even if the two signals are 180 degrees out of phase, they must still add. Ie. 50Hz + 50Hz input, regardless of phase, must = 100Hz output. All feedback appreciated, Mitch.