Shahe Linear DRO Scales

Overview

Shahe brand scales are manufactured by the Sanhe Measuring Instrument Co., Ltd. in China and sold mostly by smaller resellers. The company was the OEM for the iGaging DigiMag scales but has recently started marketing its scales directly. They offer a plethora of digital scale and gauges of all forms and shapes, including height gauges, digital indicators, digital calipers, angle gauges, etc. In particular, their "Digital Linear Scale with Remote Display" has become rather popular with machine shop hobbyists looking for an inexpensive digital readout.

Scale Models

For the purposes of a DIY digital readout, the most relevant models are their "Digital Linear Scale with Remote Display" and "Digital Linear Scale with Remote Square Display". Just like the venerable iGaging DigiMag scales, these two models use a remote display unit, are powered by a 3V battery and output 3V signal. Additionally, Shahe makes linear scales, test indicators and other measurement instruments that use the same data communication format. Unfortunately, the output signal level is 1.5V, necessitating a voltage level shifter circuit of some sorts.

Digital Linear Scale with Remote Display (5403-xxx)

This scale uses a round display powered by a single 3V; the frame and the encoder housing are made of extruded aluminum and injection-molded plastic. Unlike the Square Display or DigiMag, the USB cable is hard-wired into the display unit. Furthermore, some revisions of this scale have a Mini-USB port on the reading head, while more recent examples appear to have the cable hard-wired into the head as well.

Digital Linear Scale with Remote Square Display (5403-xxxA)

The "Remote Square Display" display scale appeared on the market after the "Round Head" model looks very similar to the iGaging DigiMag scale with some cosmetic differences in the display unit. Since the USB cable plugs into the display, this model is easier to interface with a TouchDRO adapter. The only other difference between the Round and Square Display versions is the fact that the latter uses two cells for power, while the former uses only one cell.

Vertical Type Digital Linear Scale (5401-xxx)

This scale looks similar to the 48-bit Chinese scales that were popular in the early 2000s. The frame and the encoder housing are made of stainless steel, even though the scale uses the same encoders as the scales above. In fact, the base PCB appears to have been used in the early revisions of the "Round Head" scale. Naturally, the scale uses the same 3V power supply, has the same resolution, and transmits the data using the same protocol in BIN6 format. It has one major difference: the signal level at the data port is scaled down to 1.5 Volts. This means that while it's fully supported by the TouchDRO firmware, interfacing it with the MSP430 microcontroller requires some sort of level shifter circuit.

Technical Details

5403-xxx and 5403-xxxA Models

5401-xxx Model

Data Format and Protocol

Shahe scales use a BIN6 data format that is similar to that used by the common digital calipers but with a few minor deviations. The main difference is that the calipers transmit processed position taking into account current units (inches or mm), whereas Shahe scales send raw position in native units (microns in this case). Similarly, the scales use a protocol where the reading head provides its own clock signal. Each data packet is sent a set of six 4-bit nibbles at about 9.5 Hz.

Connection Scheme

TouchDRO Compatibility

• TouchDRO Adapter board for iGaging/Shahe Scales^**
• DIY Adapter for iGaging/Shahe Scales

^** The adapter board comes with pre-installed USB Micro-B connectors. Shahe scales' pinout is different from iGaging, for which the adapter board was initially designed. In order to connect 3V scales to the adapter, a USB Mini-B breakout board is needed.

Pros

• Inexpensive
• Available around the world
• Less susceptible to flickering last digit

Cons

• Slower refresh rate
• Some models output 1.5V signal

Final Words

Shahe "Remote Display" scales have become a popular choice for an inexpensive do-it-yourself DRO. Their main drawback is the slower refresh rate that might feel laggy in some situations but this is more than offset by their low price and flexibility. That said, the "Square Display" version is more suitable than the "Round Display" version since the USB cable is hard-wired only on the encoder side.

When using these scales with TouchDRO, care should be taken to avoid ground loops; but other than that, the scales perform slightly better in the shop environment than their iGaging 21-bit counterparts. This is likely due to the more traditional communication protocol where the scales provide their own clock as well as somewhat better handling of "in-between" positions.