On Mon, Mar 15, 2010 at 10:05 AM, Bob Blick wrote: > The LM358 has a PNP input stage and is fully valid to the negative rail. > Input voltage is only limited near the positive rail for this opamp. Yeah it is okay to run with negative rail. But the circuit the OP mentioned does not have a negative power supply. http://www.edn.com/article/CA6451249.html It connects V- to Ground. But anyway, this may not be a real issue since the accuracy requirement is not that high. -- Xiaofan http://mcuee.blogspot.com -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist