Variable PSU

A variable power supply with adjustable voltage and current outputs made with the L200 regulator. Using the versatile L200 voltage regulator, this power supply has independent voltage and current limits. The mains transformer has a 12volt, 2 amp rated secondary, the primary winding should equal the electricity supply in your country, which is 240V here in the UK. The 10k control is adjusts voltage output from about 3 to 15 volts, and the 47 ohm control is the current limit. This is 10mA minimum and 2 amp maximum. Reaching the current limit will reduce the output voltage to zero.

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Audio Booster Circuit

Small and portable unit, Can be built on a veroboard

The amplifiers gain is nominally 20 dB. Its frequency response is determined primarily by the value of just a few components-primarily C1 and R1. The values of the schematic diagram provide a response of ±3.0 dB from about 120 Hz to better than 20,000 Hz.Actually, the frequency response is ruler flat from about 170 Hz to well over 20,000 Hz; its the low end that deviates from a flat frequency response.

The low ends roll-off is primarily a function of capacitor C1(since RIs resistive value is fixed). If C1s value is changed to 0.1 pF, the low ends comer frequency-the frequency at which the low-end roll-off starts-is reduced to about 70 Hz. If you need an even deeper low-end roll-off, change C1 to a 1.0 pF capacitor; if its an electrolytic type, make certain that its installed into the circuit with the correct polarity, with the positive terminal connected to Q1s base terminal.

Circuit Diagram:

 Audio Booster Circuit Diagram

Parts	Description
P1	100K
R1	47K
R2	470K
R3	10K
R4	560R
R5	270R
C1	0.1uF-25v
C2	3.3uF-25v
C3	470uF-25V
D1	5mm. Red Led
B1	9v Battery
J1	RCA Audio Input Socket
J2	RCA Audio Output Socket
S1	On-Off Switch

 

Source :www.extremecircuits.net

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Hydrophone Booster Amplifier HA2

The HP series Hydrophone Booster Amplifier (HA2) amplifies low-level hydrophone signals over a wide range of frequencies. It has a minimum gain of 25dB and an input and output impedance of 50Ω. The HA2 is designed for use with either Precision Acoustics membrane hydrophone or Precision Acoustics HP Series Hydrophone Measurement System, which is shown in Fig 1.

 

Alternatively, the HA2 may be used when the acoustic signal is provided by a high output impedance hydrophone, such as a GEC-Marconi membrane device, or a conventional hydrophone. In this instance a BNC/MCX adaptor is used which connects directly to the HP Series Submersible Preamplifier, using it as a buffer amplifier, (i.e. the standard Precision Acoustic HP Series configuration shown in Fig 1 is used, but without the interchangeable probe).

The HA2 amplifier is straightforward to use but the following points should be noted:

• The output of the amplifier should be correctly terminated in 50Ω before operation.
• The HA2 amplifier is non-inverting but this is of no consequence when used with the HP Series interchangeable probes as their design takes this into account. However when a submersible preamplifier is used as a high impedance buffer amplifier (as in Fig 2) the system output from the HA2 will be inverted as the HP Series Submersible Preamplifier is inverting.

Before Connecting the unit please read WARNING

To Connect

To  Disconnect

1	Connect Output Load	1	Remove RF Input
2	Apply DC Voltage	2	Remove DC Volts
3	Apply RF Input	3	Remove Load

Specification (HA2 Amplifier Only)

Voltage Gain = 25dB minimum
Bandwidth =  50kHz to 125MHz ±1.0dB
Maximum Output Level = 29dBm for 1dB compression (18.1V pk – pk into 50Ω load)
Input Impedance = Nominal 50Ω
Output Impedance  Nominal 50Ω (VSWR 2:1)
Output Noise Level = Typically 70μV pk – pk (bandwidth 125MHz)
Noise Figure = Typically 10dB
Phase = Non-inverting
Terminations:
Front panel = Input BNC socket BNC Output socket
Rear panel Power Requirements = 28v dc output to supply DC Coupler 100/120/220/240V ac, 50 to 60Hz,
7.5W
Operating Temperature = 0 to 50°C
Size = (90mm × 205mm ×194mm)
Weight = 2.6kg

Copyright : Precision Acoustics March 2004

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Luggage Security System

While traveling by a train or bus, we generally lock our luggage using a chain-and-lock arrangement. But, still we are under tension, apprehending that somebody may cut the chain and steal our luggage. Here is a simple circuit to alarm you when somebody tries to cut the chain. Transistor T1 enables supply to the sound generator chip when the base current starts flowing through t. When the wire (thin enameled copper wire of 30 to 40 SWG, used or winding transformers) loop around the chain is broken by somebody, the base of transistor T1, which was earlier tied to positive rail, gets opened. As a result, transistor T1 gets forward biased to extend the positive supply to the alarm circuit. In idle mode, the power consumption of the circuit is minimum and thus it can be used for hundreds of travel hours.

 

To enable generation of different alarm sounds, connections to pin 1 and 6 may be made as per the table.

 

Select 1 (Pin6)	Select 2 (Pin1)	Sound effect
X	X	Police siren
VDD	X	Fire-engine siren
VSS	X	Ambulance siren
“-”	VDD	Machine-gun sound

Note: X = no connection; “-” = do not care

Author:DHURJATI SINHA Copyright: Circuit Ideas

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Audio Level Threshold Control

This circuit was originally designed for use in detecting discharges from individual neurons, where the infrequent discharges are difficult to separate from dominant background noise. It may also prove useful in other applications that need to detect infrequent low-level audio signals against a noisy background. The audio input signal is buffered by op amp IC1 before being applied to the opposing inputs of comparators IC4 & IC5. Positive and negative offset voltages are generated by VR1 and IC2 and fed to the other two inputs of the comparators. Essentially, the comparators act to produce a negative voltage at their commoned outputs (C) whenever the audio signal exceeds either the positive or negative offset voltage.

The signal at "C" is inverted by transistor Q1 to produce "D". These two signals are used to control a pair of CMOS switches (S1 & S2), which either pass the audio signal to the output or short it to ground. The signal from the CMOS switches is buffered by IC3, which in conjunction with the 10kΩ resistor and 10nF capacitor filters out the switching artefacts. In practice, the offset voltage is adjusted until there is little or no breakthrough of the noise background at the output. Thereafter, only audio signals exceeding the threshold are passed. Inevitably, this produces some crossover distortion but this is of little consequence compared with the benefit of the quiet background.

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