I can't use a pull up. The line I monitor is the A/D convertor line. I'm getting much better results with a 2n2369, but it's still not switching consistantly. The base is connected to the A/D line via a 5818 schottky and a 47k resistor and a 6800pf bypass cap. The collector is tied to my +5v rail via a 4k7, and the emmiter directly to GND. I've tried using formulas I've found on other sites to calculate the resistor values, but my problem is I just cant be sure what the voltage is on the line when it's tristated, so I used these values based on experimentation. I'm only concerned with detecting the negative edge on the line, is there a better way to do this?