Speed of light measurement with the Analog Discovery scope

Measure the speed of light using the Analog Discovery. Digilent donated two Discoveries to the Open 7400 Competition this year, they were among the most popular prizes.

The optical pulse response of the Discovery scope shows a reasonably clean shape with a fall time of ~ 30ns and minimal ringing. With such a clean response, it is quite possible to use the low bandwidth Analog Discovery oscilloscope to measure the speed of light C, using a time-of-flight delay method with this simple gear. To provide sufficient pulse separation for an accuract measurement of C, a delay path of about twice the full pulse width, or 100 ns (or 100′ path-delay distance) is required which is easily achieveable in a modest space, with some collimation optics for the diverging LED and a tilt mirror mount. Alternatively, an inexpensive red diode laser, extracted from a laser pointer, will have sufficient modulation bandwidth to perform the same measurement, provided that the pulse circuit is carefully adjusted to match the diode laser and prevent laser damage. The second response curve below is for a 2ns wide electrical pulse directly from an avalanche pulse circuit…

Thanks Michel! Via the comments.

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