Need to block a 2Hz signal to a simple inverter
Assuming that a logic-level MOSFET has a threshold voltage of 2 volts, a circuit like







simulate this circuit &ndash; Schematic created using CircuitLab

will (sort of) work.

The idea is that, with a time constant of .45 seconds, it will take .45 seconds for R3/C1 to charge up to just about 2/3 (e/3, actually)while the input is high, but C1 will discharge through D1 during the low phase, so M1 will never turn on.

This is not a great circuit, though, for various reasons.

1) The turn-on threshold for a MOSFET is not sharp, and varies with temperature, so the output will be neither sharp nor terribly precise.

2) For the components shown, the charge current is very small, so diode leakage may be a problem.

3) C1 will not discharge all the way to ground when the input is low, since the impedance of a diode increases as the voltage across it drops. Using a Schottky will improve this effect at the cost of increased leakage as commented on in 2).