Issues w/ My Scales and Mixed Scale Controller

[s_prows]

Yuri,
I've just finished putting together the mixed scale controller kit, and I'm having some trouble with my scales.  I'm using two good quality "Chinese' scales which are both rock solid on my Shumatech DRO-350.  On the mixed scale controller, both scales work fine when the displayed value is less than (about) 6.000-in.  For larger readings, the scale is jumps back and forth between the correct value and 408.xxxx-in.  

I don't think it's a problem with the scales as they are still working fine on the Shumatech.  Also, when I inverted the scales, the problem "switched ends", that is, it doesn't correlate with a particular location on the scale.

Also,
Is the mixed scale controller supposed to work with the scales in "fast mode"?  When I set fast mode on my scales (using a switch) the touchdro readout freezes/doesn't change.

Thanks for your help,
-Steve P.

[Yuriy]

Yuri,
I've just finished putting together the mixed scale controller kit, and I'm having some trouble with my scales.  I'm using two good quality "Chinese' scales which are both rock solid on my Shumatech DRO-350.  On the mixed scale controller, both scales work fine when the displayed value is less than (about) 6.000-in.  For larger readings, the scale is jumps back and forth between the correct value and 408.xxxx-in.  

I don't think it's a problem with the scales as they are still working fine on the Shumatech.  Also, when I inverted the scales, the problem "switched ends", that is, it doesn't correlate with a particular location on the scale.

Also,
Is the mixed scale controller supposed to work with the scales in "fast mode"?  When I set fast mode on my scales (using a switch) the touchdro readout freezes/doesn't change.

Thanks for your help,
-Steve P.

Steve,
I have only one "Chinese" scale that I test with. It's 12" long and works along the whole length. If you can point me to the make/model of the scale you have, I can buy one (if it's not horribly expensive) and test the firmware with it. 
As far as the fast mode goes, the firmware *might* work but I haven't tested it in the fast mode. 
In either case, I will try to make it work...

Thank you
Yuriy

[s_prows]

Yuriy,
I think maybe I've tracked down the problem.  Take a look at the attached oscilloscope trace.

My scales are using the protocol documented in figure 6 of [url=http://www.shumatech.com/support/chinese_scales.htm].  For the oscilloscope trace in the attached file, I read a binary value of:

1001 0010 1000 1000 0000 0000 0000 (least significant bit first) = 329 (329/20,480 = 0.016-in)

for the second 24 bit word (scale relative position) with samples taken on the falling edges of the clock.   However, sometimes the data line is high during the pause in the clock signal at the end of the second 24-bit word, as shown in the attached trace.  If the least significant bit is ignored, and a sample is taken on the falling edge of the clock's ending pause, the binary value is:

0010 0101 0000 0000 0000 0001 (least significant bit first) = -8,334,069 (-8,334,069/20,480 = -409.59s)

Can you confirm that the mixed scale controller firmware transmits the second (relative position) 24-bit word? Is the data line sampled on the falling edge of the clock?

[s_prows]

Yuriy,
Some additional information that may be of use -

The data line is unpredictably low/high during the clock pauses following both the first and second 24-bit words.  However, the value during both pauses is always the same (both high, or both low).  The display skipping is positively correlated with the value of the data line during the clock pauses, but only happens for negative values of the first 24-bit word.

If I set the scale at 6-inches and remove/reinsert the battery (resetting the absolute scale zero), the value displayed on the DRO skips between small negative and large positive numbers (i.e. -0.024 / 409.576) for scale values smaller than 6".  For larger values, reads as it should.  The behavior seen on the oscilloscope does not change.  If I set the scale at zero and remove/reinsert the battery it works just fine over the full length of the scale (so, a good work-around if "fast mode" can be made to work).

So, maybe the problem isn't the "reset" alone.  Is there something special about execution of the reset associated with negative values?


- Steve P.