This simple circuit has been designed to generate sine waves with a frequency of 1 KHz while featuring low distortion and low output impedance until 1 V RMS as it obtains power from batteries.
Terminology Sine Wave – a smoothly varying wave that repeats itself which can be thought of as a projection on a plane of the path of a point moving around a circle at uniform speed where the frequency is the rate at which the fundamental shape repeats itselfBC238 – an NPN general purpose transistor used for general purpose switching and amplification due to its low current with maximum 100 mA, low voltage with maximum 45 V, and enclosed in a T0-92 & SOT54 plastic packageWien Bridge Oscillator – a type of electronic oscillator that uses an RC high pass filter and an RC low pass filter for setting the frequency of oscillation while generating sine waves without any input source Circuit Explanation
The circuit is adopting an inverted Wien bridge configuration that is comprised of RC circuits R3 & C1 and R4 & C2. In order to acquire a good overload capability, the circuit should feature a variable output, a low output impedance, and a low distortion. An amplitude waveform that is a long term output and stable is being ensured by a small filament bulb LP1 with 12 V and 40 mA rating. The operation of the circuit starts at the closing of the contacts of SPST sliding switch.
A nice long term stability with low distortion is obtained by keeping a low current type of bulb with 12 V at 40 mA to 50 mA or 6 V at 50 mA. If the type of bulb is different than the specified type in the diagram, the value of the resistor R6 should be changed to 220 Ohms or 150 Ohms. This is to make sure of the proper oscillation of the circuit. The frequency generated can be set to 100 Hz if the values of C1 & C2 are 100 nF and for 10 KHz frequency, the capacitor values should be 1 nF. Changing the capacitor values simultaneously requires the adjustment of resistor R5. Also, better performance would prefer high gain transistors.
The sine wave generator circuit may be applied in test equipments such as audio voltmeters and audio power indicator. The amplitude of the sine wave is allowed to be varied by this circuit. It can be acquired by digital to analog converters and serial port controls of personal computers. In the field of education and training, it can be used as a tool in teaching sound-related and wave-related science and physics in primary schools, middle schools, high schools, electronic-signal-related topics in vocational schools, and DSP projects in universities. Additional applications include scientific researches, industrial instrumentation, audio engineering, electronic test and measurement, musical instrument inspection, and medical diagnosis.