I connect a piezoelectric material with a LED(positive to positive,negative to negative), pressing and releasing piezoelectric material to produce a sine wave to feed LED ,and i found when i release it,the LED will light.But know i don't know which part of sine wave can let the LED light,is the positive wave part ? or a negative wave part ? I think the positive wave can let LED light,but i am not pretty sure about it.

I am not sure that the first wave is positive wave or not,i just show a normal sine wave.

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  • \$\begingroup\$ Why do you doubt LED specs that clearly state the current for forward Vf and Absolute Maximums for not to exceed -5V? \$\endgroup\$ Mar 7, 2018 at 3:52
  • \$\begingroup\$ Did you leave a comment on the wrong question? \$\endgroup\$ Mar 7, 2018 at 8:21
  • \$\begingroup\$ No. This seems to be a confusion about LED conduction polarity, but you must have Reverse Voltage protection ( ! ) \$\endgroup\$ Mar 7, 2018 at 11:53

1 Answer 1


It depends on how the LED is connected. Since LEDs are diodes, they only allow current to flow in one direction. If you were to reverse the orientation of the LED with respect to the piezo transducer, it would light when you press it down but not when released. In your example, the "negative part" of the wave is lighting the LED. If the poles were reversed, it would be the opposite.


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