Of course, the current is extremely small, but a voltage of 300 V can be obtained from 9 V of a battery. The circuit is from an Electronics Now of May 1994. C1 adjusts the operating point.
This highly sensitive light sensor was found in a 1970 General Electric documentation. The circuit...
The given number circuit is used to activate the relay by interrupting the light beam that hits...
This alarm circuit with sensors in series was found in the Electronics Now magazine of June 1994....