Re: Height Gage DRO

Hi Joe,

I've held back from commenting since my DRO experimenting tips have
been met with lukewarm acceptance. I've currently figured out several
of the cheaper caliper and scale interfaces. Wilfried Fedtke has
taken the information and built up a PCB for them. I wrote some Pic
code for it to do a simple serial and parallel interface to a PC.

By using 3-5volts and a 1K series resistor, you can find the LED
polarity safely, a variable bench supply with current meters always
helps, don't exceed the current you'd expect for a standard single LED
(10-20mA ). If you monitor the voltage across the LED leads it should
act like ~1.6-2.7 volt zener when illuminated. If it has an integral
series resistor this will affect the readings and lower the expected.

The output on the other side of the encoder reader will probably have
photo transistors (or maybe photodiodes). If they are accessible,
there probably will be a pullup on the collector side to the logic
rail (another hint at where the power is routed might be pre or post
a regulator.)

As you slowly move the carriage, the Nphase may be read at the
collector/pullup junction on a scope or meter if your patient.

I don't know about the 2 sets of lines, but I think your assumptions
are on the right track, there may be a rough scale and a fine scale
that are combined for greater accuracy..?. An absolute reference
scale would probably have some binary pattern..?. (or be a width
variation for intensity, but that would be hard keep calibrated
over temp, so probably not the case)

Are there any IC's with markings inside. Or polarized capacitors with
voltage ratings? I would guess 5Volts is in the ballpark initially
since this sounds like an older unit. Probably TTL or cmos logic.
These can be a basis for figuring out power connections and polarity.

Lee Studley
Lead Software Engineer Intersil
Broadband Wireless Modem R&D

Achieving some of the worlds fastest modem ASICs and
control DSP software.

Previous:
Qualcomm GlobalStar Test Engineer
Hypercom Hardware Engineer, Software Engineer Advanced Product R&D
Microchip Corporate Applications Engineer

--- In CAD_CAM_EDM_DRO@y..., jvicars@c... wrote:
> Upon further inspection of the old Mitutoyo height gage, the only
way
> to bring it back to life is to convert it to a DRO.
> Evidently it had a dedicated "box" to run the LED, etc that is no
> longer there.
>
> To my delight I found that it simply contains a set of gears that
turn
> what looks like a standard glass encoder disk, except that the disc
> has 2 sets of concentric encoder lines and 2 LED's
> Is there a standard for wire colors to the LED? Is black always
neg?
>
> Does the 2 sets of encoder lines give higher resolution, or is that
a
> way to keep absolute reference?