Stepper motor (3)

Hello,
In context of my previous, now outdated post...
I have found what I think would be the simplest implementation:
http://dustworld.dyndns.org/dustwolf/circut.gif
The LPT port is displayed as a set of switches which are otherwise programmatically controlled. Next to the LPT port I also have a 12 V supply from another scarped power supply unit.
Would it work or would it fry my LPT port?
Thanks in advance.
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I'd say that if the stepper coils can handle 12 volts without cooking they will probably be high inductance and the transistors will explode as soon as you switch them from on to off and the volts go through the roof. Some form of eye protection could be advisable :o)
Just my .02p
Robin G Hewitt
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The PC port was orginally driven by 74LS374 octal latch, which can source 2.6 mA and sink 24 mA. If the load pulls these lines to ground, excessive current may easily be sourced. Today, ports /should/ provide at least that or more, however some PC printer (parallel) ports only put out 3.5v when at ogic "high".
I would really suggest you look carefully at figure 3.7 at http://www.cs.uiowa.edu/~jones/step/circuits.html
Note the use of the 5.1 zener diode in the right hand circuit and the resistor in series. This limits the amount of current that can flow back into the PC port but is probably only minimal protection. In the linistepper design, the PIC microcontroller is actually the "sacrificial" protection between the motor and the PC and is protected by resistors, etc... itself. http://www.piclist.com/linistepper Without something like that, with only a resistor or without even that, your PC is probably going to be toast.
Try an old, disposable PC first.
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Use small MOSFETs for the transistors (e.g. 2N7000 series), or add base resistors to the trannies (and ensure they're high-gain types). Put pull-up resistors (around 4k7 should do) on the LPT port outputs. Put a reverse-biased diode (e.g. 1N4001 through 1N4005) across each stepper coil. Read up on how to drive steppers (phase and timing).
Steve http://www.fivetrees.com
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