Detecting a Small LED Signal in a Noisy Environment with a Lock-in Amplifier

A light emitting diode (LED) was placed at various distances away from a photodiode detector.
As the distance was increased, the output signal from the photodiode detector became very small.
At some distance, the noise signal became larger than the LED signal, so that the LED signal
was no longer observable. Lock-In Detection was used to maximize the signal-to-noise ratio for
the output of a photodiode detector so that we could “pull” the very small LED signal out of a
noisy environment. The photodiode output signal was connected to a TeachSpin Signal
Processor/Lock-In Amplifier apparatus, which was used to explore methods of filtering,
averaging, and lock-in amplification. The output signal from this apparatus was analyzed on a
Tektronix TBS 1052B Dual Channel Digital Oscilloscope.