Generic inputs

[tomcourt]

2 inputs with 1% 250 ohm either pull up (resistive sensor such as fuel tanks) or pull down (4-20mA sensor). Or open both for voltage in.

4 inputs with 1% 100 ohm pull up or 1% 1K pull up or open. 2 of these inputs also allow shorting the filter capacitor (D6(A7) and D12(A11) input pins), this would be used to support hardware based fuel flow counting.

2 inputs with 1% 100 ohm pull up or open.

Van's fuel gauge has ~250 ohm pull up. To limit the maximum current flowing to the sensor in the fuel tank and risk a possible spark, any significantly lower value pull up resistor should be avoided.

Over-voltage protection, 15K series resistor protects from -15 to 20 volts. A capacitor after the resistor provides filtering near the 8Hz sample period, 805 ceramic capacitors go to 100µF. 15K and 10µF is a time constant of .15 seconds. The capacitor also improves sampling across the input impedence (when the internal sample/hold is connected, 14pF for 6µS).

Any reason the series capacitor couldn't be 47K for better protection and allow a smaller cap?

Also input a .1 µF cap for high frequency rejection?