A 555 timer forms the basis of a simple frequency generator.
If you're studying electronics, making a frequency generator is a great introduction to circuit building. The versatile 555 timer integrated circuit, or IC, provides most of the workings of a generator circuit, needing only a few outboard parts. A resistor-capacitor, or RC, timing network determines the circuit's frequency, ranging from under one cycle per second to over 500,000 hz. You can use it as a line level signal source, tone generator or as the basis for a light emitting diode, or LED flasher. The circuit parts are all inexpensive, and you can assemble it in an hour or two.
Instructions
1. Orient the 555 timer on the breadboard so that the IC's key notch faces to your left. Insert the 555 timer IC into the breadboard so that it straddles the wide groove in the middle of the breadboard. Be careful while pressing the IC's pins into the breadboard holes and make sure none of the pins bend under.
2. Insert a short jumper wire into the breadboard so that it connects pins 4 and 8 of the IC. The breadboard is wired together by column, so you can use any free hole in the same column. Insert a short jumper wire into the breadboard so that it connects pins 2 and 6. Insert one lead of the 1000 ohm resistor so that it connects to pin 8 of the IC. Insert the other lead so it connects to pin 7. Insert one lead of one .01 microfarad capacitor so it connects to pin 1. Insert the other lead so it connects to pin 2. Take the other capacitor and insert one lead so it connects to pin 5 of the IC. Insert the other lead so it connects to pin 1.
3. Take one 1 to 2 inch jumper wire and crimp one end to the wiper -- center -- lug of the 1M ohm variable resistor. Crimp a second short jumper wire to either of the other 2 free lugs. Solder these connections and give them a moment to cool. Insert one lead so it connects to pin 2 of the 555 IC. Insert the other lead so it connects to pin 7.
4. Insert the bare end of the battery clip's positive -- red -- wire into the breadboard so it connects to the 555 timer's pin 8. Insert the bare end of the negative wire so it connects to pin 1. Insert a jumper wire at least 8 inches long so it connects to pin 3. Insert another long wire so it connects to pin 1.
5. Clip the oscilloscope probe to the long wire coming from pin 3. Clip the probe's ground connector to the long wire coming from pin 1. Turn the oscilloscope on. Set its horizontal sweep rate about 10 milliseconds, or thousandths of a second, per division. Set its vertical gain to about 1 volt per division.
6. Press a fresh 9 volt battery into the clip. You should see a pulse waveform on the oscilloscope screen. Turn the shaft of the variable resistor and observe that the frequency of the pulse changes.
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