I have seen countless times the following diagram for a Schmitt trigger oscillator.
As shown in the picture, the slow-rise wave-form generated by the charging and discharging capacitor is translated to a square wave-form at the output, as a result of the Schmitt trigger. However, I have no idea how the capacitor even charges up in the first place. I don't see any "input voltage" other than the upper and lower bounds on the actual Schmitt trigger. How is the capacitor charging up in the first place?
I'm sorry if this is a very dumb question.