Saw tooth Wave Oscillator
When you connect the signal from this oscillator to an oscilloscope, it makes a pattern that looks like the teeth of a saw (as shown below).
The shape of this wave comes from the slow charging of the 0.1 μF capacitor through the control and the 100K ohm resistor, and the capacitor's quick discharge through the PNP and NPN transistors.
The voltage divider-the 470 ohm and 100 ohm resistors-provides about 1.6 volts to the transistors. The current flowing into the 0.1 μF capacitor from the 9V supply (through the control and the 100K ohm resistor) causes the charge of the capacitor to slowly increase.
When the charge of the capacitor exceeds the voltage of the voltage divider (1.6V) the transistors turn on and provide a path for the 0.1 μF capacitor to discharge quickly. Now, the transistors turn off again, and the capacitor begins to slowly charge to repeat the cycle.
You can change the oscillator frequency by changing the values of the components in the timer circuit-the control, the 100K ohm resistor and the 0.1 μF capacitor.
Try a 47K ohm resistor or a 220K ohm resistor in place of the 100K ohm resistor, and try several different capacitors. If you connect one of the electrolytic capacitors, be sure that you use the proper polarity (+ and - ) .