Sewing machine safety mechanism

Jimmy was tired. It was the night before the county fair, and his quilt was still unfinished. Only the topstitching was left, and it was fast freehand work. Closing his sore eyes for a mere moment, he contemplated how nice it would be to finally win the blue ribbon. His hand slowly drifted under the needle...

He heard it before he felt it. The machine made an eerie grinding sound, emitted a series of angry beeps, then fell silent. Quickly flicking his eyes open, Jimmy reflexively withdrew his hand. With the dawning realisation of what had happened he slowly, nervously, examined his hand; he feared the worst.

There was no blood. No gouge, no puncture. There was a tiny scratch near the second knuckle, but Jimmy wasn't sure if was there before or not. He was a little shaken, but otherwise perfectly fine. It had worked.

The sewing machine was equipped with a new safety device, designed to prevent fabric from being ruined by messy blood stains caused by needle punctures. The needle driver mechanism was electrically insulated from the rest of the machine with plastic bushings, and connected to a capacitive sensor circuit. With proper calibration, the sensitive system could detect the dielectric presence of flesh.

Once the software determined danger is imminent, it immediately switches into full reverse, retracting the needle. On higher powered models, the safety device engages a emergency clutch as well, almost literally throwing a monkey wrench into the works. It might damage some gears, but repairing a machine is much easier and cheaper than repairing a human.

With this nerve-rattling incident, Jimmy wisely decided he had enough for the night; he had no intention of testing the safety again. There would be plenty of time to finish before the fair, and this time he was sure to win.