I remember the old mouse use a 555 to convert negative voltage to a positive voltage power supply, this maybe what you are looking for. NS may still have the application sheet available online. Funny N. New Bedford, MA http://www.AuElectronics.selfip.com ----- Original Message ---- From: Peter Feucht To: Microcontroller discussion list - Public. Sent: Friday, November 16, 2007 7:38:41 AM Subject: [PIC]: RS232 to 5V interface without supply voltage Dear Piccers, I remember, that a long time ago I saw an application note for a RS232-to-PIC(5V) interface which worked without any external power supply, but it took the needed voltages from some pins of the serial port. It had just a RS232 9 pole Dsub and 3 Pins (Rx,Tx,GND) on the PIC side. I just googled but wasn't successful. Does anybody remember such an application? Thanks for any help and best regards Peter -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist ____________________________________________________________________________________ Get easy, one-click access to your favorites. Make Yahoo! your homepage. http://www.yahoo.com/r/hs -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist