How to Design Schematic Circuit of Audio Oscillator

This circuit can be used to control the amount of current in an incandescent

lamp and also a DC motor. lf you change the amount of current through a

lamp you change its brightness. And if you change the amount of current

through a DC motor you change its speed. lnput voltage can range from 6 to

12 volts and current drain in the output is up to 2A. You can also use this

circuit in the output of a 6V or 12V fixed power supply, converting it into a

variable 0to 6 volt or 0 to 12 volt supply.

The power transistor should be mounted on a heatsink. The circuit can be

housed in a small plastic box and the heatsink with the transistor fixed on the

outside.

This low-power experimental oscillator can generate audible signals in the

range between 100 and 2,000 Hz, driving a smalloudspeaker oa low-impedancearphone. The circuit can be powered by 2 two or four AA cells or a

fixed 6 volt power supply. Current requirements for this circuit depend upon

the power supply voltage and the loudspeaker impedance and range typically from 10 to 300 mA.

Potentiometer P1 adjusts the operating frequency and can be set within a

large range of values. Potentiometers upto 1,000,000 ohms can be used,

changing the frequency range lower limit to about 10 Hz.

C1 can also be altered, and values between 0.01 and O.22uF are suitable for

experimentation. Large C1 values will produce frequencies inthe lower part

of the range.

The circuit can be used as part of alarms, games, toys and to learn more

about transistorized oscillators.

Figure I shows the schematic diagram of the Audio-Oscillator. Q1and Q2

form a directed-coupled amplifier and Rl/Cl is the closed loop that takes the

signal back from the outputo the input.

Figure2shows the layout of the components, using a terminal strip as chassis. All the components and power supply can be housed in a small plastic

box.

The key is atelegraphomemade-type switch, butyou can also use an SPST

toggle or slide switch for continuous operation. A key is recommended if you

wanto use the oscillator as a Morse Code sender in demonstrations or practice. You can wire the points A and B to the contacts of a relay to use the

circuit as part of an alarm.

Parts List - Audio Oscillator

Q1 - 8C548 general purpose NPN transistor

Q2 - 8C558 general purpose PNP transistor

SPKR - 4 or 8 ohm smalloudspeaker

K - Telegraphic key - See text

81 - 3 to 6 volts - two or four AA cells

Ri - 10,000 ohm, 114w,5% resistor

R2 - 1,000 ohm, 114W,5% resistor

Cl - 0.047 uF metal film or ceramicapacitor