>KUscroft@aol.com wrote:

>> The way we drive stepper motors at work is to take the output from a
>> PIC or other microprocessor and sent it into a 74LS374 then take the
>> output from the latch into a ULN2804.  The 74LS374 is used so that you
>> can shift out the 8 bits to be used (4 bits for one stepper, hence one
>> 74LS374 for two stepper motors + 2 ULN2804) via 2 pins from the PIC.


>OK, now you could use a 74HC164, which is designed as a shift
>register, instead of the 374.  And isn't a ULN2804 an octal buffer?  Why
>do you need two for two steppers?

No a ULN2804 is an Octal Darlington Driver array with an output (max) voltage
of 50V @ 500mA.  By tying two outputs together you get 1 Amp.  This means that
one array has four 50V 1A outputs, which can drive the steppers at work.  Also
in the IC are the common free wheeling diodes so no flyback problems.  By
using one 8 bit register ( ok a 74HC164 would do nicely ) and connecting them
to two ULN arrays you can control two steppers.

But as you say the above has nothing to do with what you were really pointing
out.  Sorry I can't help you on that one.