How about a series PTC then a shunt diode. The diode will conduct if the batteries are put in backwards, opening the PTC. Harold On Mon, 8 Nov 1999 05:26:07 -0800 mazzoni michele writes: >Hello List, > >I have realized an alarm for my bycicle using a 12C508. It is powered >by two AA >size alkaline battery. > >I would like to know if there is a simple (and economic!!) solution >which >I can use to protect my circuit against polarity inversion during >battery change. >(I know it's a remote possibility, but it exists) > >I thought to use a serie diode, but the voltage drop bring the PIC >power voltage >near the power supply limit of the MCU. > >Thanks. > > >Best regards, >Michele > >_______________________________________________________ >Are you a Techie? Get Your Free Tech Email Address Now! >Many to choose from! Visit http://www.TechEmail.com ___________________________________________________________________ Get the Internet just the way you want it. Free software, free e-mail, and free Internet access for a month! Try Juno Web: http://dl.www.juno.com/dynoget/tagj.