Pictured above is a schematic of a sine wave oscillator circuit using a transistor. We use Phase Shifter Oscillator Principal as a basic of circuit. Transistor Q1 is the sine wave generator and transistor Q2 is the buffer. Unfortunately the circuit can be used effectively only for audio frequencies i think. I have succesfully generated 100Hz, 1KHz and 10KHz from circuit above but i have unsuccesfully to generate 19KHz frequency.
There is the part list of the circuit :
| Part Number | Value | ||
|---|---|---|---|
| 100Hz | 1KHz | 10KHz | |
| R1 | 1M | 1M | 1M |
| R2 | 2K7 | 2K7 | 2K7 |
| R3, R4 | 18K | 18K | 3K9 |
| R5 | 22K | 22K | 22K |
| R6 (VR) | 47K | 47K | 47K |
| R7 | 120K | 120K | 120K |
| R8 | 1K | 1K | 1K |
| C1, C2, C3 | 39nF | 3n9 | 1nF |
| C4, C5, C6 | 10uF | 10uF | 10uF |
| Q1, Q2 | C945 | C945 | C945 |
How It Works ?
The first pulse at the collector of Q1 when the first transistor turn-on in the feedback to the base transistor through the series of phase shifter C1, C2, C3, R3 and R4. The results received pulse phase in base being turned 180 degrees. This signal then amplified by the transistor and feed back again continuously so there create oscillation process. In the part list we can see that the value of C1, C2, C3, R3 and R4 is different when we set the output 100Hz, 1KHz and 10KHz.Because output of Q1 is litle enough, so we need a buffer circuit that given by Q2. And then we also put some level adjustment that doing by R6 (variable resistor) to set the output level of oscilator. The maximum level is between 2.5 volt to 3.5volt, according fo the working frequency of the oscillator.
Error during my practice
When i try the circuit i found that different type of C945 transistor can make waveform of sine wave not perfect, it's look skewed to the left or to the right. To correct this error, i modify the base bias circuit to get to value half of vcc at the collector Q1. I hope it my help.
Download Schematic File
I made a circuit with DipTrace which can be downloaded from this link.
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