The DAXD-1 is a dual axis quadrature encoder position display
unit. It takes two sets of quadrature encoder inputs
(for example, X axis and Y axis),
and displays the current encoder position
on two 6-digit LED displays. For applications which need
higher counts, it can also function as a single axis
12 digit display. There is a switch to zero each axis, as well
as a contact on the terminal block.
The default operating mode is 12 digit single axis mode, until the X
zero button is pressed, at which time we switch to dual 6 digit
mode. To return to 12 digit mode, press the X reset while holding
down the Y reset. When switching from 12 digit display mode to 6
digit display mode, the lower order 6 digits in the current count
for the Y axis are preserved. Twelve digit display mode uses the
Y encoder inputs, and is zeroed with the Y zero button.
This device is great for tracking down problems with poor
encoder signal quality, or encoder noise. It has 2 error
indicators, which warn of possible signal problems. It
reads the encoder phases 14 million times per second. It
expects to see only a single phase change at one time, and
the signals to change state at a rate of less than 7 million
times per second. This means, that at most, there should be
no change in the signals every-other read. If the input signals
change on 2 consecutive samples, then an error is latched. This
condition is displayed as the ones digit decimal point.
The other error flag is tripped if both encoder phases are cought
changing in the same sample. In this case, the 10s digit decimal
place is turned on to indicate the error. In either case, once an
error flag is tripped, it remains on until the axis zero button is
pressed. This allows for the detection of these errors, even if
they are rare.
The board requires 400 mA of 5 volts. The power supply
should be sized larger to allow for powering the encoder.
A user provided 5 volt encoder with differential outputs
should be used. The encoder count rate can be as high as 1.75
million quadrature cycles per second. Since each quadrature
cycle is 4 encoder counts, that is 7 million counts per