On 17 October 2013 09:26, Carl Denk wrote: > Have to agree on hall effect, but I don't think it's practical at this > point. A Hall sensor could definitely be made to work. Hall sensors with digital outputs and on/off response are common. 12 VDC supply is acceptable in some cases. You can wire a 3 wire (Gnd, Vdd, Out) Hall sensor in a two wire mode so that it is supplied with power via a resistor and 2 wire lead and draws substantially more current when activated so that the drop across the resistor increases substantially. Low current Hall sensors are available that only draw 10's of uA but can switch 10's of mA so that the swing in Vdd when resistor fed can be a large proportion of rail to rail. Russell --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .