CNC is an exiting field. You program your parts in a computer and then a computer builds the parts for you. What could be cooler than this? We may not be
as close to the Star Trek’s replicator as we would like, but we need to get started somewhere, right? In that case let me help you!
I have been delving into CNC field for quite some time and although it took some time to realize all that is needed to build a CNC machine, today I can
easily summarize this in a few words: a computer, a parallel port interface card and a bunch of stepper drivers. Well, I can not build a computer into a single board much cheaper than computers are today, but
what I can do is integrate the parallel port interface card and the stepper drivers into a single unit. That is what CNCPRO25 is.
The board revolves around 4 DRV8825 bipolar stepper drivers capable of driving up to 2.5A sine wave peak. Enough to strongly move your NEMA 23
steppers! Each driver can be configured to operate either in full step or some form of microstepping ranging from half step to 32 degrees of microstepping (much more than any CNC machine will ever need),
by flipping switches on its respective DIP switch. Possible configurations are carefully documented on the board’s silkscreen.
A potentiometer selects the current the motor will operate at. A test stake is provided to measure the VREF voltage which selects the maximum stepper
current. The silkscreen shows the equation used to compute said current.
The board will accept control signals from the PC parallel port and relay them onto the output connectors, or drivers. Available
signals are that for home sensors and Emergency Button. 5V power is distributed across all sensor connectors so that a switch or optical sensor can be directly connected without the need of external components.
Sensor connectors are internally pulled down. The following table shows the signal ordering: