Quote Originally Posted by boldford View Post
As I've no need to machine metals I'm thinking of Hall Effect devices. I'm concerned mechanical switches or slotted opto devices might be affected by dust. No firm decision made yet.
No need to use hall effect... simple magnetic reed switches work well although need debouncing just as a microswitch would. A hall effect device might just be too sensitive. With modern high-strength mini-magnets I found for one application I needed the hall effect device over 5cm away from the magnet before it stopped recognising it. Also the reed switches in burglar alarm sensors are ideal and not expensive £3.99 from maplin or £1.45 on ebay