Well if you have a brass crank, why not just a rotary encoder on its shaft and a zero position sensor at one end of the travel of the pointer. -- Bob Ammerman ----- Original Message ----- From: "ivp" To: "Microcontroller discussion list - Public." Sent: Friday, February 05, 2010 6:29 PM Subject: Re: [EE] Material suggestions for slide switch >> You may have already thought of using a rotary potentiometer with >> a ~100mm diameter pulley on it, and use a string attached to the slide, >> in the style of a dial cord in old radios. > > If it's robust enough in the long term (got a bit of a downer on carbon > pot > tracks but you can get conductive plastic, at a price) that might be a > goer > > The client has indicated he'd like the slider moved by a brass crank. !!!! > This probably means that the slider will be on a lead screw and several > turns of the crank will move the pointer from one item to the next > > The reason being that this is a museum exhibit of a 1906 Edison cylinder > player, which has been motorised but originally was wound up with a > crank, so he wants to keep some of that feel to it. The selector is to > pick > a song to play from a bank of WAV files > > If the resolution proves too fine for the ADC to differentiate 20 > positions > reliably I should be able to come up with a scheme to divide the pot > travel > across more than 1 ADC > > As the slider has to move a great deal further than the pot shaft some > step-down gearing would be needed to convert 200mm linear movement > via a lead screw to 270 degrees of pot rotation > > I even thought of a stepper motor as a pulse-emiting encoder but can't > guarantee that it will keep track or be returned to an end stop to reset > the > pulse count > > My idea with a long PCB is that it would have fixed resistors and solid > detentes, thus turning the crank is a WYSIWYG. It's for public use and > something I'd rather not have to service or field complaints about > > wbr > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist