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Sound activated light

Discussion in 'LEDs and Optoelectronics' started by Phil H, Mar 4, 2017.

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  1. Phil H

    Phil H

    Mar 4, 2017
    hi thanks in advance for any help
    I'm an amateur musician!
    As a stage prop I'm planning on putting a small red light inside an old dolls head. I would like it to light up only when I press my keyboard to use a voice vocoder. So kind of like a red light coming on as a robot voice sounds. I know nothing about electronics so any help would be much appreciated. The cable the sound carries would be like a guitar lead of which I would like to plug into prop so that the prop is in between instrument and amplifier! I'm sure there must be a small electrical gadget I could build or buy? But I just have no idea what pieces to ask for! Any help would be much appreciated! Thank you
  2. SalRu


    Mar 16, 2017
    May a microphone be enough?
    When it detects a sound it generates a current.
    You connect the microphone to an amplifier and then connect the output of the amplifier to a red led through a 300ohm resistor.

    This way when you make some noyse the red led flashes

    Hope to be helpful!!
  3. Audioguru


    Sep 24, 2016
    A microphone is not wanted and is not needed because the sound signal is in the cable that is fed to the prop.
    The maximum allowed reverse voltage for an LED is only 5V so it needs to have a reversed diode parallel to it.

    The typical current for an ordinary 5mm LED is 20mA then with a 300 ohm resistor the average amplifier voltage must be (20mA x 300 ohms) plus about 2V for a red LED= 8V but the LED is lighted for only half-cycles so the voltage must be doubled. That is 8.45V RMS which is a power of 9W into 8 ohms.
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