Centrifuge setup with circuit logic controlling uranium enrichment (Kovarex Enrichment Process recipe, level 2 productivity modules).
Manual startup required: To get the process running, you need to insert 40 units of uranium-235 into the system (via the requesting chest / input buffer). Only once this threshold is exceeded will the circuit logic unlock the inserters and let the centrifuge start working on its own, continuing to produce U-235 with a net surplus through feedback.
Below the 40 U-235 threshold, the setup stays idle (no "signal-check" output from the comparators).