This circuit was found in a documentation of the 80s, having didactic purpose. For R1 values between 10k to 1M can be used. Transistors are general purpose types.
The duty cycle of a Schmitt Oscillator can be programmed by R1 and R2 in this circuit. The...
This circuit is from a Popular Electronics from 1992. It uses two SCRs and can be triggered by...
This simple SCR alarm circuit was found in an old Poptronics, but can be easily assembled as all...