This circuit was found in an English publication from the 70s, an article that teaches how to calculate instruments. The circuit is still current and can be built with an analog indicator of 100 uA.
This circuit of a 1978 American publication monitors a telephone line by triggering a relay. The...
Found in 1965 General Electric technical documentation, this half-wave circuit controls shunt type...
The power supply shown in the figure provides voltages between 0 and approximately 15 volts, with...