LPF Switch with gate inverter

The LPF is triggered automaticaly by the dedicated LPF Control from the board and a darlington circuit using a UDN2981 because the logical level at the output of the 74LS145 are inverted. My initial design was using 8 NOT gate transistor design but with the UDN2981 it makes it far easier. you can use also an alternative circuit using a CD4069 with a ULN2804 (the ULN2804 and CD4069 are able to sustain 12VDC logical drive)