The only drawback with this circuit is that it might latch in the conducting state if the load is too heavy or if there is a short at the output, this requires some kind of protection, on the input line, in the form of a fuse or similar.
If you wish to take a picture of a fleeting event which generates a sound, you can do it with this sound activated trigger. It does not require any power supply: it feeds on the high voltage available on the flash trigger terminal. Any economic ceramic microphone is suitable for the purpose. The 68nF capacitor introduces a small delay in the operation of the flash and may help in getting the picture in exactly the right moment although you should expect to take several shots for best results. With this circuit you will be able to catch a cork leaving the champagne bottle or the moment a balloon is punctured. The whole circuit could be assembled in the mike housing making a very compact device.
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