Hi All, For some of the optocoupler chip, e.g. 4N27, there is a pin coming out from the base of the phototransistor. The phototransistor senses the light coming from the photodiode to turn itself on or off, so what is the base used for? Thanks in advance! John -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist