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". Like the venerable iGaging DigiMag scales, both use a remote display unit and are powered by a 3V battery. The data signal itself sits at the 1.5V level, which is one of the reasons these scales connect through the Shahe scale converter rather than to the adapter directly. Shahe also makes linear scales, test indicators, and other measurement instruments that use the same BIN6 data format.

Digital Linear Scale with Remote Square Display (5403F)

The "Remote Square Display" scale is very inexpensive and readily available around the world. The scale uses an extruded and anodized aluminum frame, a fiberglass-backed encoder strip, and a plastic head housing. When these scales first appeared on the market, Shahe called them 5403-xxxA (to distinguish from the "Round Display" model without the "A" suffix), but a few years ago they made a few cosmetic changes and renamed the model to 5403F-xxx (sometimes listed as 5403-xxxF as well). The scale's Mini-USB cable plugs straight into the Shahe scale converter.

These scales have three major shortcomings. First, the plastic-on-aluminum construction results in poor repeatability due to mechanical play between the frame and the main PCB that contains the capacitive array. Second, the signal level is 1.5Vpp, which is very susceptible to noise. Finally, the scale has a relatively slow refresh rate of 9.5Hz, which can feel laggy on the quill.

Vertical Type Digital Linear Scale (5401-xxx)

This is a more premium Shahe scale with a ground stainless steel frame, stainless steel housing, and a built-in display. Electrically, it's similar to the 5403 scales (and the early revision of the "Round Display" scale used the same PCB), but for some inexplicable reason Shahe chose to use a different Mini-USB port pinout, where the "ID" line carries the "Data" signal.

Mechanically, this scale is superior to the plastic-on-aluminum 5403F scales, and offers better accuracy (less local error) and repeatability. Published accuracy is 0.001"/6" versus 0.002"/6" on the aluminum models, but in our testing the difference was much more stark.

Unfortunately, wiring this scale to TouchDRO is not easy. Not only is the pinout different, but 5-wire Mini-USB cables with the ID line connected don't exist (ID was not used by mainstream Mini-USB devices). Thus, to connect this scale to a TouchDRO adapter, you will need to build a custom cable with the Mini-USB connector wired for your 5401 scale on the scale end, and the 5403F pinout (used by the Shahe scale converter) on the other end. Moreover, since Shahe scales output a 1.5V signal, it's critical to use a shielded cable with the shield connected to the ground on the TouchDRO adapter end.

Digital Linear Scale with Round 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. Because the cable is hard-wired with a nonstandard pinout, connecting this scale to the Shahe scale converter requires a custom DIY USB cable.

Technical Details

5403 and 5403F 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

All three Shahe scales use the BIN6 protocol and are read by current-generation TouchDRO adapters (TDA-410, TDA-420, and DIY kits) through the Shahe scale converter. You need one converter per axis. The converter supplies regulated power, handles the clock, and takes care of signal-level conversion, so the scale's voltage is not something you need to design around. What differs between the models is the cable:

• 5403F "Square Display" — directly supported. The USB cable plugs into the display with a standard pinout, so it connects to the Shahe converter as-is.
• 5403 "Round Display" — supported with a custom cable. The cable is hard-wired into the display with a nonstandard pinout, so a DIY USB cable is needed between the scale and the converter.
• 5401 "Vertical Type" — supported with a custom cable. It uses the same nonstandard pinout as the Round Display and needs the same DIY USB cable.

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.