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Figure 10 - Adding the two circuit boards into a small project box
Figure 10 - Adding the two circuit boards into a small project box

My sound activated camera was going to be installed on location for some security job, so I installed the two circuit boards into a small project box as shown in Figure 10. The plastic box will also have enough room to hold a 9 volt battery and a power switch to turn it on and off. To run a 5 volt circuit from a 9 volt battery, you only need to include one other component - a 7805 regulator to step the voltage down to 5 volts. If you alter the voltage on this circuit, you will also have to readjust the sensitivity, but this is made easy by using a chassis mounted variable resistor so that it can be set anytime.



Figure 11 - The completed sound activated camera, waiting to spy on trespassers
Figure 11 - The completed sound activated camera, waiting to spy on trespassers

Figure 11 shows how my completed sound activated camera looked after installing the two small circuit boards and battery into a plastic project box. The knob is attached to the variable resistor VR1 to allow easy adjustment of the sound sensitivity, and the electret microphone is installed on the side of the box so that sound can enter through a small hole in the plastic.



I also included an external 1/8 audio connector so that I could activate the camera from an external microphone or some other voltage signal. Since the LM358 op-amp comparator can be set to respond to just about any changing voltage, other devices such as light operated circuits, or motion activated circuits could be used to trigger the camera. Having a high resolution camera responding to some external event makes for a very useful security device, able to pick up the smallest details in a scene, even when placed at a long distance from the subject.
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