Variable Frequency Audio Project
This basic electronic project can be used as a low level alarm generator or a code practice oscillator. It is centred around MC34119 IC which is a low power audio amplifier. It provides a differential speaker outputs to maximize output swing at low supply voltages(2.0 V minimum). Coupling capacitors to the speaker are not required. It has the following features.
a) Wide Operating Supply Voltage Range. (2.0 VDC to 16 VDC)
b) Low Quiescent Supply Current (2.7 mA Typ) for Battery Powered Applications.
c) Chip Disable Input to Power Down the IC.
d) Low Power–Down Quiescent Current. (65 mA Typ)
e) Drives a Wide Range of Speaker Loads. (8.0 W and Up)
f) Output Power Exceeds 250 mW with 32 W Speaker.
g) Low Total Harmonic Distortion. (0.5% Typ)
h) Gain Adjustable from <0 dB to >46 dB for Voice Band.
i) Requires Few External Components.
The schematic below shows the basic schematic of the project. In this circuit, the output of MC34119 at pin 8 is fed back to input at pin 4 through the RC network. This controlled positive feedback causes the amplifier to go into oscillation. The frequency of oscillation can be varied from 250 Hz to 4 kHz using the 50K potentiometer VR1. The chip disable input pin 1 is kept high using the R2 resistor. As long as this pin is high, the amplifier does not operate. Once it is pull to ground by the key K1, the oscillator will turn ON. This circuit can be modified to suit any application that needs to sound an alarm when a certain event happen by controlling the key K1 electronically.
Parts List
