Re: noise on microprocessor data line



Josh wrote:

Eeyore wrote:
jsutinen@xxxxxxxxx wrote:

I have a pair of Hall sensors (Allegro A1101's FYI) feeding into a PIC
microcontroller (16F505) (directly into data ports) and I am having a
terrible noise problem. The noise arises from the fact that a single
DB9 serial cable carries both the sensor signals and power for an
electric motor. There is nothing I can do to separate the motor power
from the sensor wires so I need to do something at the microprocessor
board.

Are the hall sensors open collector ?

Graham

Yes they are. The previous revision of the controller had pullup
resistors on the data lines to the PIC but I noticed the PIC has its
own internal pullup so I'm going to try leaving them off this time
around (also to help determine why every couple months the PIC would
burn out).

The use of open collector outputs is the reason you're picking up so much noise.
Try sticking 470R in as an extra external pull-up.

Graham

.

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