At 08:44 PM 2/28/2004 -0500, you wrote:
> > At 03:49 PM 2/28/2004 -0500, Spehro Pefhany wrote:
> > Gustaf:  Connect the zener to GND rather than 5V. Other than that, it
> > looks good. Why the LS244?
> >
>
>I don't understand sending the zener to ground.  If I go from 5v to
>the motor commons, and then to ground, that's just a zener diode between
>5v and ground. On the other hand, if you mean I should put the zener
>going to ground on pin 9 (gnd pin of ULN2803) then I sort of see what
>you mean.  Which is it?

Cathode of the zener to pin 9, anode to ground (or +12 is better,
actually, provided the zener voltage isn't too high). You could just
connect pin 8 to 12V, but that would reduce the performance of the
motor.

>By the way, the wiring I have used is based
>on this wiring of a ULN2003:
>
>http://www.doc.ic.ac.uk/~ih/doc/stepper/control2/connect.html
>
>Is the diagram on that page incorrect?

No, it's fine. The problem with connecting it to +5 when the motor
is running off 12V is that you're pumping energy from the motor
inductance into the 5V bus. This could be bad, as voltage regulators
don't sink current only source it. The 5V bus will then increase
until the PIC or the LS244 dies.


>Why the LS244...
>I put the LS244 in for paranoia; I don't want to blow up my computer's
>printer port.  So, I thought that I would try to not sink current from
>the printer port to drive the PIC.  Of course, I don't know if it's
>actually doing anything.  I used the LS244 to send data into input
>pins on the parallel port on another project, to buffer the lines going
>into the printer port and offer some protection to the computer from my
>circuit (or something connected to it).

Mm. Okay. You could just use some resistors too. With 12v on the circuit
you have more reason to be concerned.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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