The current limit circuit (see diagram) compares this voltage to an adjustable negative voltage using an op-amp wired as a comparator – unlike many op-amps, LM324 op-amps can be used as comparators ...

I was planning to use the opto-coupler speed sensor as part of a motor speed control - making the motor ... due to dc resistance in the motor (see diagram). So that any speed droop when loading the ..