This circuit was found in an old Poptronics. Operational amplifiers can be replaced with equivalents. The power supply must be symmetrical.
This circuit, for older machines, fires a second flash with the light received with the first, thus...
This circuit was found in a 90s Popular Electronics. The circuit indicates if a transmitter is working,...
Here is another project that is based on an astable multivibrator, in a demonstration of the...