# Switching a Circuit on-and-off In-step with the Rotation of a Drive-shaft (Mechanically)

I'm working on a project. The Salient part here is a drive-shaft connected to a bearing, onto which a simple circuit is mounted. I want to switch the circuit on every $$π$$ and off for the other $$π$$ of a full $$2π$$. In other words, I want it on for every half rotation. I want to do this mechanically because non-mechanical solution seem like they might be hard to sync. Also, the solution needs to interfere with the machine's operation as little as possible. It is a complex machine that will be subjected to high moisture and so forth, so ideally, the switching system would entirely co-rotate with the shaft.

I don't know if there are any 'ready made solutions,' or not, but i'd be thankful to be pointed in the right direction (towards something plausible), or told I should wing it and create something from scratch (presumably because there isn't any solution that can simply be bought at a hardware shop).

thanks.

• Does your simple circuit have have a micro-controller. A micro-controller will solve your problem. Commented Jul 17, 2020 at 1:20
• @MahendraGunawardena Thanks for the answer, but I would think that would have issues because the thing involves variable RPM. Commented Jul 17, 2020 at 1:41
• @MahendraGunawardena In addition, I'd rather not complicate things too much with sensors, ETC... Commented Jul 17, 2020 at 1:43
• 2 magnets, a sensor and a relay that stays on until the next pulse. Commented Jul 17, 2020 at 7:15
• How fast is it spinning? Commented Jul 17, 2020 at 7:20

Without a sketch your setup is difficult to visualise. A typical industrial solution would be to use an inductive proximity switch. These are non-contact, fast switching, water-proof, etc.

Figure 1. A selection of inductive proximity switches.

You seem to suggest that the switch and circuit will rotate. This means that you need to consider those forces applied to the sensor and any rotor imbalance that the switch may cause.