I am attempting to wire up limit and spindle index sensors using some small honeywell opticals. I have a 10K pull up in the circuit. My issue is that it does not seem that the circuit will draw the port pins low consistently. It will draw the port down to ~1.4V when bread boarded and 1.8V when soldered to a piece of PCB.
When first connected it work fine, when I block the sensor, it drive the output high (~4.5v) when I unblock the sensor, the voltage does not go low enough to reset the LED on the Mach 3 Diagnostics screen.
Basic schematic
to LPT Pin
l
10K l NPN
+5v-----^^^^^-------l------------\_/-------- Gnd
I have tried using larger pullups , up to 1M, it doesn't seem to make a significant difference.
Any thoughts?
Randy