Re: Pull Up Resistor Sheridan Edward Ethier wrote:

> I checked the ECHO signal and found it to be at 2.0V when plugged into
> TIC3 on the HB.  I also applied a pull-up resitor which did send ECHO
> to 5V when not pinging.  However, in both cases, I still had seemingly
> random positive and negative values returned from the sonar.
>
> Any insight would be appreciated.

 I just checked my copy of the Polaroid Sonar Module documentation, and it does in
deed state that the module can sink up to 0.1 mA when ECHO is pulled high.  It
sounds like your module is drawing around 0.064 mA = ((5V - 2V)/47Kohms), so it is
in spec; but even so 2V is *not* a valid CMOS level (anything between 1V to 3.5V is
not a valid input according to my 68HC11 doc).

So first thing, I would use the 4.7K pullup!

But that said, it sounds like you have something else wrong.

Do you have access to an oscilloscope?  If so you could verify the timing of the
interface pins.

Later,

    Rick


