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VUE32 4CH ANALOG

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Revision as of 18:46, 10 December 2012 by Jfduval (Talk | contribs)
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VUE32 External analog inputs

ESD:

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

About R5:

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).

Opamp:

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

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