Using an RCA integrated circuit, this instrumentation amplifier was found in a November 1970 Radio Electronics magazine. The instrument has a full scale of 100 uA.
This National Semiconductor circuit appears elsewhere on this site. The circuit must be powered by...
In this circuit the frequency is determined by the coil and the variable capacitor. Transistors like the...
This circuit is from old American documentation, but the transistor used is still very common...