Rich Ottosen wrote:
>
>Good to here that your board is mostly working.
>
>Roman mentions checking if there are back EMF diodes on both the supply
>and ground sides. Even more important is to check if there are diodes at
>all. I seem to remember that not all versions of the L293 have the
>diodes.


Hi Rich,

The pic-o-board is working fine - I am just trying to nail down
operation for the worst case situations. The Handyboard, which also
uses the L293D chips, swears people off using it with the little 3v
motors, but I think it's a layout and ckt design problem in their
case. One msg I ran across indicates that cutting some HB gnd trace
and rewiring it elsewhere cures the problem.

With a nice [expensive $20] 12vdc 100mA gearmotor, there is no noise
problem at all with my board - must be good brushes. The little 3vdc
motors cost $1, and I guess it shows.

However, with everything I have on the board, the 3v motor noise is
manageable I think - diodes in L293D chips, transzorb + bypass/reservoir
caps on motor buss, isolated gnds/busses between logic and motors,
snubbers on the motors, etc.

I also have small series Rs in all control lines leading from the PIC
to the motor ckts - as past experience had convinced me these Rs are
the single best way to protect PIC pins from many hazards.

best regards,
- dan michaels
www.oricomtech.com
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