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<title>555 Sawtooth Oscillator</title>
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<p>
This is a simple
<a href="http://en.wikipedia.org/wiki/Sawtooth_wave">sawtooth</a>
<a href="http://en.wikipedia.org/wiki/Electronic_oscillator">oscillator</a>
using a
<a href="http://en.wikipedia.org/wiki/555_timer_IC">555 timer chip</a>.
<p>
A timing interval starts when the trigger input ("tr") goes lower than 1/3
V<sub>in</sub>, or 3.33V. When this happens,
the 555 output goes high, and the 555 waits for the threshold input ("th") to
reach 2/3 V<sub>in</sub>, or 6.67V. A PNP transistor acts as a
<a href="e-currentsrc.html">current source</a> to steadily charge
the capacitor. The threshold
input slowly rises until it reaches the
required level. Then, the timing
interval ends, and the capacitor is quickly discharged through
the "dis" input.
<p>
When the capacitor is discharged enough so that the trigger reaches 3.33V,
then a new timing interval begins. The end result is a sawtooth wave.
<p>
Next: <a href="e-555lowduty.html">555 Low-duty-cycle Oscillator</a><p>
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