A previous Design Idea describes an astable multivibrator that gets hysteresis from the positive feedback stage using a technique you can characterize as positive-capacitive feedback (Reference 1). It ...

produces standard 60-Hz power and 180-Hz power for "high-cycle" concrete vibrators. According to Multiquip, the unit typically can handle up to three of the company's 2-inch high-cycle vibrator heads, ...

A free-running generator built on the standard configuration of the 555 timer can't provide a duty cycle of exactly 50%. That's a well-known fact. Fortunately, there are several ways to get around ...