This circuit indicates when a rain is acidic by monitoring its pH. The circuit is from a 90s RE Experimenter Handbook. Some components used can be difficult to obtain today.
In the figure we have the way to obtain an adjustable 1 to 10 mAconstant current source. The...
We found this circuit in an old General Electric documentation. In fact, PUTs are not common...
This alarm uses several sensors that directly trigger a sensitive relay. A larger relay can be...