At 07:24 AM 8/29/2010, you wrote:
>Had another look at data sheet - pin 3 specifically says that it is open
>collector.
>So your circuit could be
>
>pin3 - 10k - *** +5 *** Volts
>PIC connects to pin 3.
>Note that tere is an internal divider.
>Divider can be 323, 64 or 128 (see page 2 rhs to see how divider is set).
>SO pin 3 changes state at least 32 times faster than the stepper motor lea=
ds
>do. No problem for PIC but needs noting.
>
>Note that my pin 4 / pin5 suggestions may still work OK as their current
>source appears to be simply (the supply voltage) /  (meter resistance +
>resistance from pin 4 to ground).
>This is PWM modulated by the IC, providing the meter drive. Note that the
>mark-space ratio on pin 5 varies with meter drive level - frequency may/wi=
ll
>also vary.
>
>Nathan - this may be starting to sound all a bit complex. t isn't really b=
ut
>there are a range of options and the IC does some interesting things.
>
>The original suggestions of either a resistor plus zener or my two resisto=
r
>divider (plus small capacitor) seem the simplest easiest and cheapest.
>
>
>
>           Russell

If there is any distance between the grounds (of the PIC and the tacho chip=
)
a series resistor of ~1K - 10K would be highly recommended in the case of
using a pullup to +5. (view with fixed-width font).



                         +5V
                          |
                         .-.
                         | |
                         | |
                         '-'
         .--------.       |  ___    .---------.
         |        |--\\---+-|___|---|         |
         |        |                 |         |
         |        |                 |  PIC    |
         |        |                 |         |
         |        |                 |         |
         '--------'                 '---------'
             |                           |
             +--------\\-----------------+------------ GND



>Best regards,

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



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