iGaging Absolute DRO Scales

iGaging Absolute DRO+ Scales

iGaging Absolute DRO scales were introduced to the market several years after the iGaging DIgiMag scales. These scales offer several notable upgrades, including a true absolute encoder strip, stainless steel frame, reading head body, and faster native refresh rate. Similarly to the classic DigiMag scales, Absolute DRO Plus scales first came out with a USB Mini-B connector and later switched to a Micro-B. The latter uses the same pin mappings as the DigiMag/EZ-View scales. The former, unfortunately, uses a completely different connection scheme, so a simple Mini-to-Micro adapter can't be used to connect these scales to the TouchDRO pre-made adapter board.

Scale Models

There are two different models of this scale. The original version branded as AbsoluteDRO (without "Plus" designation) used USB Mini-B cables and a proprietary data protocol that is incompatible with any of the TouchDRO firmware versions.

iGaging AbsoluteDRO Plus looks identical to the first version except for the inclusion of the word "Plus" on the display unit. They initially came with USB Mini-B cables, but relatively quickly switched to USB Micro-B connectors.

Technical Details

Power supply voltage 3V
Scale frame connection Ground
Resolution 10 micron/0.00039"
Material Stainless Steel
Accuracy 0.001"/6"
Refresh rate 50Hz
Available lengths 6”, 12”, 24”, and 36”

Note: iGaging advertises these scales as being IP54, which has lead some people to believe that the scales are coolant proof. IP54 states that the scales have "Limited protection against dust ingress" and "Protected against splash water from any direction." In reality, the IP54 rating means that the scale has some way to keep dust out, which is no different from any other linear scale on the market.

Data Format and Protocol

iGaging AbsoluteDRO Plus scales transmit the data in a format that at first glance looks very similar to Mitutoyo Digimatic SPC format. There are a few important differences between them, though. Although the number of bits and approximate flag bit position is similar, iGaging decided to use binary encoding rather than BCD (binary coded decimal), so some flag bits are unused and/or can be ignored. Furthermore, iGaging doesn't use the request/acknowledge scheme and simply sends the stream at a predefined frequency as long as the "Req" line is pulled low.

Oscilloscope screen capture of iGaging Absolute protocol
iGaging Absolute Data Stream

Connection Scheme

As mentioned earlier, iGaging Absolute DRO+ scales come with either Mini or Micro USB cables. Unfortunately, for some reason, iGaging decided to change the pinout when switching to Micro-B cables, therefore adapting Mini-B scales to Micro-B adapters requires the use of breakout boards or custom-made cables. Also, please keep in mind that the cables used with Absolute DRO+ scales have five wires. Since the vast majority of Mini-USB cables on the market come with 4 conductors, you will likely need to carefully bridge Req. and Ground lines on the reading head.

USB Mini-B Pin Functions

USB Pin TouchDRO Line
5V Ground
D- Data
D+ Clock
ID 3.3V
GND Ground

USB Micro-B Pin Functions

USB Pin TouchDRO Line
5V 3.3V
D- Clock
D+ Data
ID Ground
GND Ground

Hard-Wiring the Cables

When using a DIY DRO adapter, many people opt for simply cutting the connector off and soldering the cable to the PCB. This provides a simple and secure connection, provided there is adequate strain relief. If you decide to use this approach, please keep in mind that there is no standard conductor color scheme. This means that you will need to use some other way to figure out which wires carry which signal.

Fortunately, there are clearly marked test points on the PCB. By testing the continuity between them and the wires you will be able to reliably identify the signal lines.

iGaging Absolute DRO+ Scales internal test points
Internal Test Points
Test Point TouchDRO Line
VDD 3.3V
REQ Ground
Frame Ground

TouchDRO Compatibility

** The adapter board comes with pre-installed USB Micro-B connectors. Scales that use USB Mini-B cables will need to be connected using a set of Mini-USB breakout boards or soldered directly into the board.



Final Words

iGaging Absolute DRO+ scales offer a sizable step up from other capacitive scales thanks to their absolute encoder, fast refresh rate, and solid construction. Unfortunately, the scales cost significantly more. In fact, a set of Absolute DRO+ scales for a medium-sized machine costs almost as much as a set of off-brand glass scales. Unless you already own a set of these scales and are looking to upgrade to a more integrated DRO, it would be wise to choose Glass scales instead.