This setting applies to virtually any photo transistor and any operational amplifier. The power supply must be symmetrical, and the gain is determined by the relationship between R2 and R1.
This circuit triggers a relay when the detected humidity falls below a value. The system can be...
We found this circuit in an old General Electric documentation. In fact, PUTs are not common...
This alarm circuit was found in a 1997 publication. It uses two reed-switches to arm and disarm the...