This fiber optic data link set includes one transmitter and one receiver, each housed in a small plastic case, along with 5-meter and 10-meter sheathed polymer optical fiber coils terminated with clip housings. The transmitter contains electronics for producing a modulated light source with a choice of modulation: a variable-frequency audio tone (1 Hz to 1 kHz) and a 250 kHz square wave for speed-of-light investigations, which is brought out to 4 mm sockets for oscilloscope monitoring. The receiver contains a variable-gain amplifier with an integral loudspeaker and direct monitoring sockets for an oscilloscope. The wavelength used is in the visible red part of the spectrum. Both units are powered by PP3 batteries (transmitter has an accessible battery compartment).