Performance-Based Assessments for Digital Circuit Competencies

It should be noted that the input states in this circuit are defined by the voltage levels, not by the contact status. In other words, a closed contact equals a “low” (0) logic state.

The choice of diodes is not critical in a circuit where the inputs come from manually actuated switches. Neither is the choice of resistor sizes (10 kΩ) works just fine, especially when the only thing loading the output is the student’s logic probe or voltmeter.

Nothing special to note here!

It needs to be understood that this is an AND gate only if you consider the “0” and “1” states as defined by voltage levels with respect to ground, and not by switch actuation. Many students assume an actuated (pushed) switch is a “1” input and a de-actuated (un-pushed) switch is a “0” input. Not necessarily so! In this circuit, the switches are connecting inputs to ground. This means a closed (actuated) switch provides a low (0) input state, while an open (un-actuated) switch provides a high (1) input state.