On Fri, Jun 17, 2011 at 10:19 AM, james tornes wro= te: > I have an interesting problem. I have a mains circuit that looks like thi= s: > > mains---110VAC--+ on/off switch +-------------------+ load > +----------mains return > > The load is a regular incandescent light. I need to insert a 5V device > in series with the switch. The problem is that when the switch is off, > then the device also goes off. I have heard that leakage current could > be a way to still have a mostly functional switch and still be able to > provide power to the 5V device. But I haven't been able to find any > designs/circuits that show this. Anyone have any advice? Typical design is to use a SCR or IGBT. Actually all the 2-wire AC proximity switch work like this from what I see. I worked for Pepperl+Fuchs before and it has quite some such AC sensors. Same for Omron, SICK and other sensor vendors. An example: Inductive sensor NBB2-F1-US. http://files.pepperl-fuchs.com/selector_files/navi/productInfo/edb/188298_e= ng.pdf You can see that it actually works from 20 ... 253 V AC/DC Within this type of sensors, there are of course lower voltage based circuit (say 5V or 3.3V MCU or others -- I think there are no MCUs in this particular sensor but there are others which may have one). Whether this will work or not depend on the load. But if you follow the design, maybe you will have to combine the AC switch into your design. --=20 Xiaofan --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .