Aspects of the present invention provide a module including an electronic circuit that flags the presence of AC or DC input signals. An AC filter receives an input signal and couples it to a first leg. The AC filter permits an AC signal to pass to produce a first output and prevents a DC signal from passing. A DC filter also receives the input signal and couples it to a second leg. The DC filter permits a DC signal to pass to produce a second output and prevents at least part of an AC signal from passing. A lock out circuit in the first leg prevents the second leg from producing the second output when the first leg produces the first output. The output of each leg may be digitized and coupled to a logic controller to flag the presence of AC or DC input signals.