6/12/2015

Audio Amplifier Classroom Microphone System Circuit

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This audio amplifier circuit is useful in classrooms to reduce the strain of lecturing ,if the surrounding environment is noisy. It uses the power amplifier IC LM380 that gives 2 watts output which is sufficient in a confined area. The amplifier is portable and the whole circuit and the battery can be enclosed in the Speaker box itself.
The circuit uses a preamplifier stage around NPN transistor BC 548 and a power amplifier around LM380.An external Collar MIC can be given to the input using an audio jack .The voice signals are amplified by T1 and fed to IC1 input through the volume control VR. Capacitor C3 reduce the undesirable howling from the speaker.
LM380 is the general purpose audio amplifier and its gain is internally fixed at 34 dB. Its output is short circuit proof with internal thermal limiting. The IC works between 5 to 22 volts DC and is dual in line version.


Classroom Microphone System Circuit Schematic

Audio Amplifier Classroom Microphone System Circuit
Audio Amplifier Classroom Microphone System Circuit

Assemble the classroom microphone system circuit on a common PCB. A 9 volt PP3 battery can be used to make the unit compact. If the amplifier is used for many hours, a 6 Volt 4.5 Ah rechargeable battery is a nice choice. If it is used, a charger input facility should be provided .Use a small good quality 8 Ohms speaker. If the output is not sufficient, use a high power amplifier IC circuit in the place of LM 380.

LM380 Pin connection

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Audio Noise Filter and Bandpass Filter for Audio Frequency Band

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Audio Noise Filter and Bandpass Filter for Audio Frequency Band

This audio noise filter circuit is a bandpass filter for audio frequency band. It filters unwanted signals that are lower or higher than the audio frequencies. It has 2 filters: a low pass filter and a high pass filter in a cascade configuration. Both filters are second-order filters with a 24 dB/octave fiter capability. The 3 dB cut-off freq. are 11.8 Hz and 10.7 kHz.
Audio Noise Filter and Bandpass Filter for Audio Frequency Band
Audio Noise Filter and Bandpass Filter for Audio Frequency Band


The bandpass characteristic can be changed by changing the values of the capacitors and resistors. If you want to raise the bottom cut-off freq., you must reduce the values of C1 up to C4. For lowering the bottom cut-off freq. you must increase the values. If you want to reduce the top cut-off f you must raise the values of R5 up to R8 and decrease it in order to increase the top cut-off frequency.

Noise Filter circuit diagram



Audio Noise Filter Parts List
R1 = R2 = 56kΩ
R3 = 39kΩ
R4 = 100kΩ
R5 = R6 = R7 = R8 = 3.3kΩ
C1 = C2 = C3 = C4 = 0.33µF ceramic
C5 = C6 = 0.0033µF ceramic
C7 = 0.0047µF ceramic
C8 = 0.0018µF ceramic
IC1 = IC2 = NE5532N
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6/04/2015

Classic Tone Control Circuit with Low Noise Transistor

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Classic Tone Control Circuit with Low Noise Transistor

Tone control is a type of equalization used to make specific pitches or “frequencies” in an audio signal softer or louder. A tone control circuit is an electronic circuit that consists of a network of filters which modify the signal before it is fed to speakers, headphones or recording devices by way of an amplifier.Tone control allows listeners to adjust sound to their liking. It also enables them to compensate for recording deficiencies, hearing impairments, room acoustics or shortcomings with playback equipment. For example, older people with hearing problems may want to increase the loudness of high pitch sounds they have difficulty hearing.
Tone control is also used to adjust an audio signal during recording. For instance, if the acoustics of the recording site cause it to absorb some frequencies more than others, tone control can be used to amplify or “boost” the frequencies the room dampens.
Classic Tone Control Circuit with Low Noise Transistor

This classic tone control circuit uses a low noise transistor model which is interesting. The transistor makes the adjustment more suitable for the person to hear. The variable resistor also plays an important role in controlling the output. In the simulation it was transformed into a voltage divider theory having 50% resistance each. Notice the blue color waveform is the control output while the black is the input. For further simulation please see Project Link.
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6/03/2015

Wireless DIY Hardware Keylogger

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This is a do it yourself wireless hardware keylogger project, consisting of a logging unit with a 2.4GHz transmitter, and a USB-based receiver. The project includes the schematics, PCB design, firmware, software and lots of additional files and data. A wireless keylogger is a perfect solution for monitoring user activity, at very low risk of disclosure, is a purely electronic device, so no access to the operating system is required.
The Wireless Keylogger consists of two main building blocks: the transmitter, and the receiver. The actual keylogging takes place in the transmitter, which is in fact a PS/2 hardware keylogger, with a built-in 2.4 GHz wireless module. Captured keystroke data is transmitted through the radio-link in real-time, rather than getting stored. The receiver on the other hand, is a wireless acquisition unit with a USB interface. All keystroke data received from the transmitter is sent to the host computer via USB. From the software side, this data is available through a virtual COM port, allowing any terminal client to be used for visualizing keystroke data.

If you decide to create your own Wireless Keylogger, you should have some basic experience with electronics and soldering, ideally with SMT (Surface Mounted Technology). The easiest option includes ordering a kit with components from us, and doing the soldering, cabling, and final assembly on your own. This involves having a temperature-controlled soldering iron and quite good soldering skills.
If you decide to design and produce the PCBs yourself, you should have significant experience in this field and proper equipment.
Wireless DIY Hardware Keylogger
Wireless DIY Hardware Keylogger


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