A versatile low-cost interface module that features optical isolation

The complete design and construction of a versatile low-cost interface module are presented. This module functions as a combination pulse lengthener-stretcher with an added feature of optical isolation between the input and output circuits. It is useful in interfacing many behavioral and physiological instruments that utilize different voltage levels and polarities in their respective logic systems. The cost of the components needed for module construction (without power supply) is approximately $15.