If you're an electronics student or hobbyist, who has done some basic work with op-amps, you're ready to tackle a simple oscillator. The oscillator uses the op-amp's gain and feedback to produce fairly pure sine waves at a fixed frequency. Engineers call this a Wien-bridge oscillator, and while more complex designs have better stability, the Wien-bridge makes the most of its few parts. Once you have the components in front of you on a workbench, you can easily put it together in under an hour.
- 741 op-amp integrated circuit (IC), dual in-line package
- Two, 1K ohm resistors
- 2.2K ohm resistor
- Two, 1 microfarad 50V capacitor
- Two, .1 microfarad 50V capacitor
- Assorted lengths of #22 insulated jumper wire
- 12 volt DC bipolar power supply
- Prototype breadboard
Insert the 741 op-amp IC into the prototype breadboard, which is an electronic circuit. Notice that the breadboard has channels spaced to accommodate integrated circuits, so one set of legs fit on either side of the channel. Make sure to orient the 74, so the notch or dimple faces to the left. Pin 1 of the 741 will be toward you on its lower left.
Insert one lead of a 1K resistor into the breadboard, so it connects to pin 3 of the 741. Insert its other lead into a free column on the breadboard. Insert one lead of a .1 microfarad capacitor connecting it to pin 3. Insert its other lead into the same column you used for the resistor, putting the resistor and capacitor in parallel. Insert one lead of another 1K resistor so it connects to pin 3, and connect its other lead into a new free column. Insert one lead of another .1 microfarad capacitor into this free column, and insert its other lead so it connects to pin 6 of the 741.
Insert one lead of the remaining 1K resistor, so it connects to pin 2 of the 741. Insert its remaining lead, so it connects to an unused breadboard column. Insert a jumper wire, so it connects this column to the first free column you used, which now connects the first 1K resistor and .1 microfarad capacitor. Insert one lead of the 2.2K ohm resistor, so it connects to pin 6 and connect the other lead to pin 2.
Connect all three lines--positive and negative ground--of the 12 volt DC power supply to the breadboard. Make sure each line goes to a separate free column on the breadboard. Insert a jumper wire, so it connects the power column for ground to the column you used to connect the first resistor and capacitor. Insert another jumper wire, so it connects the +12 supply column to the 741's pin 7. Insert another wire so it connect the --12 column to pin 4. Insert one lead of a 1 microfarad capacitor into the +12 supply column, and the other lead into the supply ground column. Insert one lead of the remaining 1 microfarad capacitor into the --12 supply column, connecting the remaining lead into the ground column.
Insert a jumper wire, so it connects to the 741's output pin 6 and leaves its other end dangling. Double-check all connections. Turn your oscilloscope on and clip its input probe to the free end of the wire connected to the 741's output. Clip the input probe's ground to the power supply ground. Set the oscilloscope sweep rate to about 10 milliseconds per division, and set its vertical scale to about .5 volts per division.
Turn the power supply on. The oscilloscope should display a nice sine wave.
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