I need to feed a very fine nylon thread in a process by controlling a spool motor. There is not enough pull on the thread from the process to have the thread activate a push-button, even with a 1"-long lever on the button. Anyways ideally there should be no tension on the thread, so I guess you can say I want "slack management".
The system is controlled with an MCU but it doesn't really matter, all I want is a signal when the thread begins to tension to activate the feed motor for a few seconds (it is a 1/3 RPM 120VAC synchonous motor controlled by a SSR relay). I am not very well versed in mecanical things, perhaps there is a mecanical solution to this. I checked sewing machine-type thread tension regulator principles but these rely on a strong pull from the needle mechanism to regulate via springs, as I stated earlier the process can't and shouldn't pull on the thread.
As far as electrical detection goes, I am too newbie to know many solutions. I was thinking perhaps when the thread is slack it could rest on a plane with two contacts, shunting the gate of a mosfet to ground in a (very) high impedance input circuit, kind of like a "touch button" circuit. I'm not sure the thread has enough conductivity for this, I'll go now and check that, but perhaps someone can already tell me that can or can't work.
Of course all solution suggestions are welcome. Thanks in advance, J.