We found this circuit with duty cycle adjustment in the May 1988 Radio Electronics magazine. The source must be symmetrical, and the frequency given by R3 and C1.
This circuit was found in a Electronics Handbook (1989). The shown amplifier provides a few...
This circuit was found in the October 1993 Electronics Now magazine. The output transistors form...
Several types of OSEPP sensor modules can be obtained from Mouser Electronics for Arduino...