We found this circuit with JFETs in a Radio Electronics magazine from June 1969. The circuit has its assembly described in a complete article. Equivalent transistors can be used.
This circuit, obtained from old documentation, doubles the frequency of the pulses applied to the...
The passage of an object in front of the LDR, producing a shadow or even turning off the ambient...
The CMOS TLC555 [equivalent to the bipolar 555] can be used as a monostable in the configuration...