optoisolator interfacing questions i am interfacing some simple circuits that run on v to my cpu board which runs at v the optoisolator is a n on the led side i put the signal i want through a k resistor to the base of a n on the transistor side i tie my cpu input line to the collector which has a pull up resistor of k it functions ok but seems very slow i can detect pulses that occur at about khz but not much faster isn t the rise fall time of this device something like us i should be able to detect my target of khz but i can t get khz this is done using wire wrap and the wires going to the cpu and to the test pin are about inches long but i m not doing anything high speed in the art of electronics it mentions tying the base of the phototransistor to ground through a resistor to improve the speed is that what i need to do how do i calculate the resistor value paul malenfant pmalenfa kitkat webo dg com
