This circuit oscillates in the fifth harmonic of the crystal frequency. The circuit is from a 90's documentation. L1 must be according to the desired frequency.
This metronome configuration with the 555, quite common was found in a 90s Hands On Electronics. The...
We found this circuit in a 1964 Electronic Design. Transistors can be modern general-purpose...
As monostable we have a proximity switch that can be used as a shield, since the capacitance of...