In this experiment, we measure light delay in 15 meters fiber cable using TDC7201 Time to digital converter. I used common parts you can find any where easily. All fiber cables in here are Toslink optical cable and very cheap. My measurement is 99.2[ns] in 15 meters cable. If it is in vacuum environment, light would travel same distance in 50[ns]. Normally refraction index is 1.3 for fiber cables but this cable might be different I used 10 meter fiber cable in same brand, at that time my measurement was 65.8[ns]. So same fiber cable result is correlated.

Part list:

• Arduino Due or similar micro controller which has SPI and 3.3V logic level
• TI TDC7201 evaluation board [http://www.ti.com/lit/ds/snas686/snas686.pdf]
• Red light laser
• 2 photo diode
• 7404 for basic laser diode driving (or any transistor based driver would be fine)
• OLED or other display [Optional] Because, output is also printed to serial terminal
• 15 meters optical cable
• Optical Splitter

Arduino Due codes: https://github.com/hasanunlu/tdc_7201