For measurements between 30 and 40º C this circuit was found in the documentation of 1968. The sensor is a difficult component to obtain today.
Found on 90's Popular Electronics, this circuit triggers when the microphone picks up a sound. The...
Found in a publication from the 60's, this circuit uses the CK722, germanium transistor of the...
This simple circuit can use any general-purpose transistor. The power supply must be isolated. The circuit...