This circuit is from a publication from the 70s. The operational amplifier is from the period. Modern equivalents according to the motor current must be used.
The figure shows how to use an LM3914 with a variable range moving point. The circuit has an...
This circuit was found in a 90s Popular Electronics. It uses a varicap that admits equivalents. The...
This circuit is from an Electronics Now from 1998 and can be easily assembled with other JFET...