Capacitor help (sawtooth signal)

Hi guys, I am using a PIC Micro to generate a signal of 11hz per second (i.e. it pulses 0 and 1 eleven times per second), which will generate a squarewave signal.
I want to modify the signal to output a 'sawtooth' signal. How do I calculate the capacitor value to use?

Is there a formula to use where I input Voltage, frequency etc.

Thanks

A resistor and a capacitor (LP filter) will generate an exponential sawtooth (some curvature in the slope of the sawtooth) with a square-wave input. The higher the amplitude of the sawtooth in relation to the square-wave amplitude (determined by the RC time constant), the more slope you will see. If you select the time constant to give a small amplitude sawtooth and then amplify it to the desired level, the slope can be fairly straight.

If you want a perfect sawtooth with straight slopes, you will need a current source driving the cap, or use an integrator circuit (op amp or transistor).

Three circuits: