This Schmitt optical trigger with LDR was found in old documentation. The relay must be sensitive, or an additional step must be used to trigger it.
In the figure we have the way to trigger a 7555 CMOS monostable with a positive pulse. The time...
This circuit is from a 1968 documentation. It generates a non-symmetrical signal with the waveform...
This circuit is from the manual of the used operational amplifier itself. The same setting can be...