The 1: 1 transformer on this circuit found in a 1967 Electronics World can be wrapped around a small ferrite rod. The circuit operates with 600 to 6 000 Hz control signals.
This circuit was found in a 1987 publication, but it can still be easily assembled today as the...
This circuit uses a common diode as sensor. The output goes from 0 to 10 V with the temperature change in...
This circuit, from an old publication, can also use modern transistors. Note that the unit is...