Feedback in public address amplifier is something that should be avoided. The ideal solution is by adjusting the microphone and the speaker position, but it`s not always possible in many situation. Using frequency shifter to change the output frequency 10Hz lower than the input frequency can solve the problem, but it`s too expensive for a low cost
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public address system. Voice operated switch is one cheap working solution (see the circuit`s schematic diagram). LM346 is programmable operational-amplifier. According to its data sheet, by pulling the SET pin(s) to V- the op amp(s) shuts down and its output goes to a high impedance state. Using this property, the LM346 can be used as a low speed analog switch for VOX (Voice operated switch) application. The figure below shows the schematic diagram of the VOX circuit. The first op-amp is the buffer for the microphone with gain=2. The second op-amp and the diode 1N914 is configured as peak follower, follow immediately the signal peak but falls down slowly because the charge of the 10uF capacitor can`t be sinked by op-amp output (blocked by the diode) and must be discharged slowly through 10M resistor. This slow discharging ensure the voice signal is not muted at short silence between words and sentences. The third op-amp is configured as a comparator, which its reference is adjustable via 10k Pot. This potentiometer should be adjusted to set the proper level where the sound activate this VOX circuit. The last op-amp doing the voice muting, when the control voltage output drop to zero because no sufficient sound level detected on the microphone. Connect your microphone to MIC IN, and connect the AUDIO OUT to your microphone input of your amplifier. The CONTROL output of this VOX circuit is provided to control other...
This project fits more for custom made battery casing that can have more space to hide things inside. This switch with few alterations can be used for any other project as well but is designed based on e-bike needs! This project use a clever functionality of....
The circuit described here uses ultrasonic oscillations and operates based on the propagation velocity of these oscillations in the air. Thus, we can easily determine the distance of two points if the time within which the wave travels this distance is....
Sometimes the precious metals are hidden too deep and are not detected except with complicated devices. In many cases, however, small pieces of precious metal buried near the surface can be detected by relatively simple means. Everyone is very attractive to....
Many times for various reasons we forget or can not water the plants that we have in our homes. And many humidity sensors units just notify us with a beeping sound or with a flashing light, that the pot needs watering. But what if we are away from home? This....
The principle behind a metal detector is really very simple. Proof of this is the circuit that follows, in which it proves that the construction of a metal detector can be done in the minute, with few components that we find very easily everywhere. With the....
The sub-harmonic bass generator is a sound producing unit for guitars. The sound it produces looks very much like that of the bass guitar. The octave generator is sometimes quite unusual since it does not produce any of the usual ways of coloring the sound,....
In the past the sounding (sea bottom measurement) was done with the "bullet", that is, with a heavy lead object that the seamen plucked into the sea hung from a calibrated rope. As soon as the "bullet" reached the bottom, the depth appeared directly from the....
This Amplifier was designed to have the following specifications: Distortion less than 0.1% at full power of 100W even at 20KHz. Power has to be attributed to an extended bandwidth. The output transistors must be protected against short circuits. The power....
A series of LEDs serve to alert the gardener when plants need water. Using two conventional digital integrated LEDs and a series of LEDs, we make a very useful device for gardening. The device detects the amount of water in the pot and alerts the grower.....
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