Electronics Online

This simple amplifier circuit will be nice for newbie project/junior student. Require an IC LM386N to build a mono channel amplifier. There are few components such as capacitor, resistor, potensiometer and speaker in this circuit, so the students will know the real shape of components.

Parts List :

Capacitors :
C1, C5 2.2 uF / 50Vecap _________2
C2, C9 10 uF / 25V ecap _________2
C3, C7 100 nF mono (104) ________2
C4 100 uF / 16V ecap ____________1
C6, C8 470 uF / 16V ecap ________2
C10, C11 47 nF mylar (473) ______2

Resistors :
R1, R2 10 ohm ___________________2
Pot 1 10k ohm stereo pot ________1

Misc. :
IC 1, 2 LM386N __________________2
8 pin IC socket _________________2

This anti theft circuit uses timer IC 555 to produce the sound. The alarm will keep “silent” when the thin wire is connected the pin 4 of IC to the ground. When the thin wire is broken, the alarm will set to “crying”…

This is a police alarm circuit.  The two 555 timer ICs used as astable multivibrators. The frequency is controlled by the pin 5 of the IC. Actually, the sound is genereted by combination of sound from both IC 555. One timer generated low frequency and the another generated high frequency. By varying VR1 you can set how fast the siren changes from high freq. to low freq. VR2 sets the siren frequency.