At 06:55 PM 4/19/2007, Vitaliy wrote: >Second, and I should have probably >mentioned it, I would like to affect the lines as little as possible. We >have designs which are powered from the port, and it's not a good idea to >add more load to the port (voltage drops below threshold). > >Any other ideas? Not sure if this will give you the results that you want, but similar to what Rob described but with NPN & PNP buffer transistors. Series R from signal line into both bases, both emitters tied together and to one end of bi-color LED, other end of bi-color LED through resistor to ground. PNP collector to -4.5V, NPN collector to +4.5V. One more (high-value) resistor between bases and emitters keeps the LEDs off when not in use. You can get a dual PNP & NPN transistor in what looks to be a sot-23-6 package (BC847). Of course, you can have lots of variations on this theme but I'd try to stay with emitter-follower topology for highest input impedance. Small and darned inexpensive. dwayne PS - This Canadian seller has reels of 3000 pcs of BC847 for US $30. dwayne -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 22 years of Engineering Innovation (1984 - 2006) .-. .-. .-. .-. .-. .-. .-. .-. .-. .- `-' `-' `-' `-' `-' `-' `-' `-' `-' Do NOT send unsolicited commercial email to this email address. This message neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist