Quote Originally Posted by martin54 View Post
A lot of bobs have a seperate 5v power connection so if your parallel port runs on a reduced voltage then you can supply the 5 volts from a separate power supply. One of the main reasons for people switching to smooth steppers is not so much the problem with the parallel port voltage but the operating system they are running, you need a 32 bit system for mach3 to work with a standard parallel port bob, those with 64 bit systems have problems with the parallel port drivers which is why they go down the smooth stepper route.
No your wrong Martin.? It doesn't work like that and is a common mis-understanding of BOB's and the PP.!

The parallel port (PP) voltage relates to signal voltage and has completely nothing to do with the powering the BOB.
When you see BOB's stating can be run from 5V that doesn't mean it comes from the PP and actual doesn't. Often they take it from either a USB port or a separate external supply.

Regards the low power parallel ports the problem comes from the way drives and control system deal with the signals. Drives/Control sys expect or watch for the signal to have only 2 states.? ON and OFF also known has HIGH or LOW.
The way the system distinguish's between HIGH / LOW state is by watching the PP signal voltage and setting a threshold IE: 0-2.4v = LOW 2.6 - 5v = HIGH. I'm genralising the voltage has it fluctuates but a good system will have a clear separation with LOW being close or = to 0V and HIGH nearer 5V.
So if you have a 3v or 3.5v PP the system still expects LOW to be in the 0 -2.4V range and HIGH 2.6 -5V but with a 3V PP you only have 0.5v margin left to distinguish HIGH from LOW and this low margin is what causes the problems.
It's just not enough margin to keep a clear line drawn in the sand so to speak and makes for a very unstable system.!! Just the slightest electrical noise can flip the signal either way and cause mayhem.!!

I can tell you now 90% of smooth stepper users buy them to get away from the PP or because there PC is modern and doesn't have a PP more than to use 64bit PC's.