This circuit uses a crystal phone and can be built with more modern transistors like the BC548. The original circuit is from a 1979 publication and is powered with only two AA or AAA batteries.
This simple photometer uses a 1 mA milliammeter and a common phototransistor. The circuit has its...
The component values depend on the current, which in this case has a maximum value of 5 A. The...
I found this circuit in an article in a 2003 publication. The circuit is an example of how to...