Figure 0 - This circuit will add sound activated control to a camera
This circuit will add sound activated control to a camera

This simple project will add sound activated control to any digital camera by ending a time controlled pulse into a relay board that is connected to the dual stage camera shutter switch. The sound is picked up by a sensitive microphone and then fed into an operational amplifier set up as an adjustable comparator so that the sensitivity can be controlled. The level of sound activation can be adjusted to respond to very faint sounds such as voices or footsteps and also adjusted to only respond to loud sounds such as music or hand claps. As a security device, this project will allow a high resolution image to be captured in response to some type of nearby sound.

This project makes use of a circuit from a previous project called "Camera Trigger Hack", which is a pair of relays and drivers fed into the shutter release switch on a digital camera in order to mimic the original functionality of the switch. You could probably feed the output from this circuit directly into the camera shutter switch, but to be safe, the relay adds a level of isolation from the camera circuit board. Some cameras also have an external remote control jack. This could also be used.

Figure 1 - This is the relay interface that controls the camera shutter switch
Figure 1 - This is the relay interface that controls the camera shutter switch

The small board shown in the left of Figure 1 is a previous project called "Camera Trigger Hack", and it allows any electronic device to issue a focus and shoot command to the camera. I call this a hack because it requires removal of the original switch from the camera in order to hack into the two functions that control the focus and shoot signals on the cameras circuit board. You "may" be able to build this project without the previous project as long as your camera board will accept the 5 volt digital signals from the 74121 one-shot into the cameras board, but to be safe, this previous project adds a level of safety to ensure your camera will not be damaged by any external device or voltages.

The small circuit board shown in the right of Figure 1 is the board that will be presented here, and it consists of a small microphone, an op-amp preamplifier (LM358), and a digital one-shot switch (74121), which controls the pulse time to the relay board that will trigger the shutter release switch. The one-shot is needed as the camera expects the shutter release to be pressed down by a human, and the pulses sent from the microphone preamplifier will be much too short to be taken seriously by the camera. The one-shot takes this millisecond input pulse and then sends out a digital pulse for a duration that is long enough for the camera to respond.

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