Dwayne, the reference you mentioned cannot be traced down for some reason, so could you please elaborate a little about what you used in the practical circuit ? Like, what is the expected AC pk-pk level (approximately) on the sensor at room temperature ? And do you tie C and B together on the transistors used for sensors ? Peter -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics