Some help please

114

01:43:30

I built this circuit on a breadboard and when I left the capacitor as shown in the diagram and then touched it or moved it slightly the LED turned on. Any explanation for this?

published 6 years ago

Leopy

6 years ago

You are capacitively coupled with the main (120/230V, @50/60Hz) basically everywhere, as long as you are touching the ground (the effect is still present but less pronounced if you are not in contact). So basically you are charged and discharged, even by several volts, at any moment through the environment (not much charge, though. Not even enough to feel it). When you touch the cap, you basically apply that signal to the base of the BJT, that amplifies the current and lights the LED. This effect cannot be simulated in a SPICE, though.

Randomplayer

6 years ago

So this could be used instead of a capacitive touch sensor?

clintdarocha

6 years ago

Leopy

6 years ago

Well, it can work as a capacitive sensor up to a limit. The limits are the output current (consider using a mosfet or a darlington trans), and other limitations like unpredictable behaviour if battery-powered or used in different environments than the ones it's calibrated for.

Randomplayer

6 years ago

Thank you Leopy

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