We found this circuit in a 1980s documentation. Equivalent components can be used. The circuit senses temperatures in the range of 0 to 50º C and uses a transistor as sensor.
In the figure we have the way to increase the current capacity of an operational amplifier. The...
We found this circuit in a 1982 documentation, but the circuit can still be easily assembled, as the...
Found in an Electronics World of 1968 this circuit can use any SCR and diodes depending on the...