ktmodelshop
Newbie level 3
I am setting up a cnc router. Stepper drive board appears to be ok. Control signals come from a pc running a program called Mach3. This program creates step pulses and inclludes a driver for the pci port (parallel, d25). This pc runs a 3.3 v board. and all outputs from the port should run rail to rail which is the case for various direction and enabling signals. The pulses, however, run about 500mv. No one, including the software designer, seems to know why this is so i put it down to some pecularity of this pc. I thought the easiet solution would be to pass these pulses through a comparitor to be switched to full voltage so i put an LM139 on a breadboard, set up a voltage divider pot for reference and onother one to test the input and it worked perfectly down to 10mv or so. But here is the mystery! The signal pulses pass directly through from input to output unchanged, no swing to vcc. The pulses are set to have a length of 5us, well with the capacity of the LM139. I have no clue. Any thoughts?:?:
thanks, Ralph
thanks, Ralph