I am working on a application which can monitor zones with sensor which produces +5 volts in normal conditions but the output floats when there is alarm condition detected. floats means that the line is not at 0V or sinking any current nor any voltage.

I am using a NPN transistor as suggested by mahmood Elnasser. (His suggestion is given below). This has solved my problem that when there is +5V in sesnor... transistor output near 4V's other wise if there is 0V or float then transostor produce 0V.


Now the problem is that i suspect that there will be very long lines between sensor and the device with this interface. i do not want that a false alarm be generated by the system because of long line in potentially noisy environment. please give me suggestions

thanks
Shahzad






mahmood Elnasser's suggestion from previous posts which i am using
"use any NPN transistor with base pulled down to ground by a 10k resistor and 10k resistor between your sensor and base of transistor.
Now you can have your output to port pin of microcontroller inverted ( with 10k pullup resistor between collector and +5v) where collector of transistor goes to port pin, emitter goes to gnd. Or not inverted with 10k between emitter and gnd, Emiter goes to port pin and collector of transistor goes to +5v
Regards"