Drew Vassallo wrote:
>I'm using a 16C71 on a project, but as it is a very old project, I have some
>instances of poor electrical design :)  One instance of this has RB5
>directly driving a normal radio control servo, which consumes much current
>(I believe somewhere around 300mA, but I haven't measured it).  It seems to
>work fine with the 16C71, but when I switch my code over to a 16C715, the
>chip itself becomes VERY sensitive to lower supply voltages, somewhere
>around 5.10V and below.  If I move the servo too fast, the chip often
>resets, or sometimes just pauses for a moment, then continues with normal
>operation.  I think this is because the servo draws more current when it is
>in rapid motion.
>
>I guess my question is more of a request for affirmation, but could the high
>current draw directly from the pin be causing this intermittancy?  Have I
>possibly damaged the PIC in any way permanently?  I will, of course, add a
>transistor to drive the servo, but I guess if there are other problems, or
>if this isn't the cause of the intermittancy, I'd like to know what they
>might be, anyway.
>


Drew, it sounds like your problem is not excessive current draw from
the PIC, but more likely noise from the motor is resetting the PIC.

Servos usually have 3 pins, gnd, power, and signal. You apply a
pulse train to the signal pin to move the servo, but the actual
high current for the motor comes from the power pin. A PIC pin
could not drive enough current to spin the motor, I would think.

You probably need more filtering on the servo power/gnd pins.
Also, it's possible you need filtering on the signal pin too,
and maybe /Mclr on the PIC.

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