VUE32 4CH ANALOG
VUE32 External analog inputs
Special care is needed to operate electronics in a harsh automotive environment. To protect the PIC32's analog inputs, two diodes are used to clamp the ESD pulses to the supplies.
Low Pass filter (LPF):
fc = 1 / (2*pi*R*C)
fc = 1 / (2*3.14*16*1e3*10*1e9) = 995Hz ~ 1kHz
R5 is used to provide a DC path to GND so the input is never floating. It assures a steady "0" when the input is not externally connected. However, as noted on the schematic, 100k is not a good choice. It forms a voltage divider with R3. The DC gain is:
G = R5 / (R3 + R5)
G = 100k / (16k + 100k) = 0.86
Using R5 = 470k is recommended (G = 0.97).
With R1 = 0, IC1A is a unity gain buffer. It's used to lower the impedance of the node connected to the analog input. By changing R1's value, you can add a gain to the signal.
G = 1 + R1/R6 = 1 + R1/1k