This circuit was found in the July 1994 issue of Electronics Now magazine. The relay can be rated at up to 12 V and 100 mA. The transistor is a general purpose transistor.
A constant current source can be built based on one of the LM3900 or LM2900 amplifiers, as shown in...
This circuit was found in a 1973’s Japanese magazine. It uses transistors of the time and is...
We found this circuit in a 1980s General Electric documentation. It appears from other sources in this...