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Electronic Amplifier Circuits-Power amplifier, audio amplifier designs and circuits

May 30th, 2010

Window Foil Burglar Alarm Circuit

Circuit Description

The circuit diagram of window foil burglar alarm has been published here. The main parts of this circuit are SCR H1 (TYN 612) and transistor Q1 (BC 107). This burglar alarm can be fitted in windows to check breaking attempts.

Here the sensing element of break attempt is a network of fine wire element fitted through the window glass. At normal condition, the transistor Q1 will be in off state since its base is connected to the ground. Then SCR will be in non-conducting state since it has not been triggered. When a break attempt of window comes, then the wire elements will break and the base of transistor will connect to positive potential. This turns on Q1 and the output of it triggers SCR.  This turn on of SCR turn horn to blow and the circuit remains on unless power supply is switched off.

Circuit Diagram

Window Foil Burglar Alarm Circuit

Window Foil Burglar Alarm Circuit

Notes

  • To setup the circuit, make switch S1 open and adjust R2 to get a 1V between base of Q1 and ground. Now transistor will be conducting and horn will be blowing.
  • Now, close S1 and reset the power supply .The transistor Q1 will be off and horn will not be blowing. Then circuit is ready.
  • Make a loop of very fine wire through the window glass to make the window foil (two or three lines running in both direction is enough).

May 30th, 2010

Simple Tweeter Crossover Circuit

Circuit Description

The circuit diagram of tweeter crossover circuit has been described here. The advantage of this circuit over circuits of single coil speaker is that it can handle both high and low frequency signals simultaneously. A tweeter circuit can produce a better sound clarity than single speaker circuit if low frequency is filtered out from the amplifier output.  That principle is applied in this particular circuit. Here a low pass filter circuit consisting of elements C1, C2 (25 uF) and potentiometer R1 (100 ohm) is used for filtering high frequencies. This filtered output is given to the tweeter (K2). The existing woofer (K1) is driven with the low frequency.

Circuit Diagram

Simple Tweeter Crossover Circuit

Simple Tweeter Crossover Circuit

Notes

  • The power rating of potentiometer should not be less than 2 Watts.
  • Use electrolytic capacitors for C1 and C2.
  • The tweeter can be a 2 to 3 inch, 4 to 8 Ohm one.
  • Potentiometer R1 is used to adjust the output level of tweeter to that of woofer to match both.
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