I have been studying the schematics of drivers and interface boards on your site. This has been a tremendous help and I have learned a great deal. However, I have some basic electronics/setup questions.
First, I noticed on the joe version of the ss3977, he has connected pin 9 to +5v. On your version, pin 9 is not connected. Is the pin 9 connection redundant, since logic devices (the 74HC14 inverter on the ss3977 driver, and the TLP627 optoisolator on the 3 axis bob) have their own power sources and internal pullups? Same thing with the driver's 74HC14 and the direct connection into the computer's parallel port in the 4 axis bob? Both sides of the connection have internal power and pullups?
Another question about optoisolation: If the 8-35v power supply is powering the interface board and the drivers they are sharing ground. Is this okay? Is it considered optoisolated - if the power and ground is coming from the same place, but vreg'ed in different places? It seems that for true isolation, two separate ac-to-dc power supplies with separate transformers drawing power from the mains need to be used.
I also noticed the inputs to the computer are not isolated on the 3 axis bob. Could that be isolated by just reversing the same methods used with the computer outputs - using TLP627's? They probably do not need isolation since they will only be connected to switched or photointerrupters.
I am learning pic programming, so I am also interested in the picstep. On your picstep page, you write:
4. On the opto isolated interface board, you will need a separate isolated 5VDC source to power the opto isolator output and the PIC.
5. On the opto isolated interface board, depending on opto isolators you may need to remove the 2 10K pullups on the Step and Direction signals.
A small board inserted between the opto interface and the picstep, which has a vreg and some filtering, would do the trick in powering the picstep. Correct? Again, if ground and power for all boards and their vreg's is coming from the same primary power supply, is that considered isolated?
In reguards to line 5., the 3.3k resistors on the interface and the 10k's on the picstep are redundant and just draw extra current, by being in parallel, correct? Removing the 3.3k's on the bob or the 10k's on the picsteps would do the trick, right.
Thanks for any advice or comments, and your site. The 3 axis computer/interface/drivers/switches picture was definitely worth a 1,000 words!