... with an operational amplifier. I often build this circuit when i need some clock signal for a digital curcuit, but more often if I need a type of triangle signal to build a pwm circuit (yes, it isn't a real triangle, but good enough for pwm where it is only important that the signal is symetric).
+ only a few components
+ nearby supply voltage independent
+ never gets broken (my circuit for light regulating works since 5.2013)
+ drains not very much current
+ max. frequency is only limited by the speed of the amplifier
+ you can adjust the frequency while operating by replacing the resistor under the opamp with a potentiometer
- not suitable for real triangle wave generation
