Eindhoven University of Technology has made a photodiode with such low noise (<10-6mA/cm2 dark current) and wide dynamic range (<150dB), that it can optically detect a heartbeat at a distance of 1.3m.

In [AM]’s example, he is measuring the intensity of a laser using a photodiode with a crude amplifier, but even with the amplifier it’s hard to see the signal in the noise. By adding a PWM ...

What many of us may be unaware of though is that an LED is also a photodiode, and can even be persuaded to generate usable quantities of power. [Voltative] takes a look at this phenomenon with a ...