>Steve, this uses just two lines. Alright. I'll admit it. This muddle headed wombat is still very confused. 1 x Pin to pulse counter in 4017 decade counter to select band pass filter +1 x Pin to reset 4017 decade counter to default known start state = 2 pins 2 pins + 1 pin for controlling the low pass filter selection = 3 pins. vs 3 pins Binary Coded Decimal (BCD) to control *both* low pass filter selection and the output band pass filter selection. Two different ways to arrive at the same level of control. But is it not still 3 pins = 3 pins? So where are we saving an IO line? I'm probably being completely daft and missing the flaming obvious but I just can't see it. Help! 73, Steve.