Simple BJT not gate pull down

This is a simple logic inverter (NOT gate) using an NPN BJT. An SPDT switch and a square wave were provided to serve as input signals. Switch Ssel selects between these two input sources. Slogic is intended for Interactive mode while the square wave is intended for Transient mode. A base-to-emitter (also base-to-ground) resistor, consisting of fixed (Rbefxd) and adjustable (Rbeadj) parts, is provided which can help discharge the capacitances shunting the base and emitter of the BJT, the base-to-emitter resistance also shifts the switching threshold of the input to a higher voltage. The rise and fall times of the square wave were set so that the threshold can be conveniently observed.