This Linear Technology circuit can measure currents from 100 pA to 100 uA. The circuit is from the 80's, using a component of the era. Transistors are general purpose types.
In the figure we have a sensor circuit that makes use of common transistors and a photo diode as...
This unusual configuration, but which has already been explored in other articles, uses diodes in the...
This circuit uses a modulated signal from a PLL 567 to operate safely with an infrared emitter. The...