Hey, I have a few questions for those knowledgable about building circuits using basic electronics parts (ie available at radioshack, digikey)
Two unrelated questions :
1) I have a hobbyist project that uses a matching IR LED/phototransistor pair to detect the blocking of a pathway. The detector is tied to a pullup resistor and drives an indicator LED. I was having problems getting enough distance/sensitivity from the detector, so I added a 2N2222 in a darlington configuration to the photoT to increase the sensitivity of the detector. This worked wonders, tripling the beam distance I can use, but it also added a somewhat annoying slew rate to the detector. By that I mean, instead of the very quick on : off switching action of the 1T configuration, the darlington config output rises fairly slowly (0.25s from .7->4.3). It's behavior is almost as if there is a (large) capacitor that is discharging. Is there any way to remove this response lag?
2) Are there any cheap, easily available inverter/buffer DIP ICs capable of sustained sink currents of 20-40ma? All the datasheets on the likely suspects I've seen so far give abs max values of 20ma, and sustained currents of far far less than that.
Previously I've had to create my own driver by using a PNP transistor and a couple pullups from the logic outputs of my circuit, but that's becoming annoying for the dozen output lines I need to run now.
Two unrelated questions :
1) I have a hobbyist project that uses a matching IR LED/phototransistor pair to detect the blocking of a pathway. The detector is tied to a pullup resistor and drives an indicator LED. I was having problems getting enough distance/sensitivity from the detector, so I added a 2N2222 in a darlington configuration to the photoT to increase the sensitivity of the detector. This worked wonders, tripling the beam distance I can use, but it also added a somewhat annoying slew rate to the detector. By that I mean, instead of the very quick on : off switching action of the 1T configuration, the darlington config output rises fairly slowly (0.25s from .7->4.3). It's behavior is almost as if there is a (large) capacitor that is discharging. Is there any way to remove this response lag?
2) Are there any cheap, easily available inverter/buffer DIP ICs capable of sustained sink currents of 20-40ma? All the datasheets on the likely suspects I've seen so far give abs max values of 20ma, and sustained currents of far far less than that.
Previously I've had to create my own driver by using a PNP transistor and a couple pullups from the logic outputs of my circuit, but that's becoming annoying for the dozen output lines I need to run now.