Dedicated DRO Adapter for Shahe Scales

Saturday, January 18, 2020

A few years ago, Shanhe Measurement Instrument Co. introduced a new line of capacitive scales called Shahe "Digital Linear Scale with Remote Square Display" (model numbers 5403-150A/200A, etc.). Thanks to their low price and world-wide availability, the new scales have become a popular choice for budget do-it-yourself DRO builds. Unfortunately, these scales use Mini-USB connectors with pinout different from the iGaging DigiMag, which precluded the use of straight Mini-to-Micro USB adapters to connect them to the TouchDRO Adapter for iGaging scales. To offer a solution that didn't require soldering, I was planning to sell a kit that included the adapter board and a set of USB Mini-B breakout boards that could be connected with ribbon cables. The feedback I received from most of the "Beta" users was that the result was rather awkward; so instead, I decided to design a dedicated adapter board that is pre-wired for Shahe 5403-xxxA scales.

Since the TouchDRO Adapter for iGaging Scales already works very reliably with these scales, I decided to base the new PCB on the existing layout and simply swap the USB connectors. As a result, the adapter for Shahe 5403-xxxA scales is almost identical to the latest revision of TouchDRO Adapter for iGaging scales with two exceptions:

  • It comes with pre-installed USB Mini-B connectors wired specifically for the Shahe scales
  • Mini-USB connector pins are not broken out to a 5-pin headers

Supported Scales

This TouchDRO adapter version is pre-wired specifically for Shahe Digital Linear Scale with Remote Square Display (models 5403-150A/200A/300A/500A/600A/1000A).

These scales look very similar to the classic iGaging DigiMag scales, which have been sold outside of the USA under Shahe brands. Despite their similar appearance, they use completely different internal electronics and communication protocol. Since the new adapter is wired specifically for the Shahe scales, it can not be used with iGaging DigiMag, even the ones that came with Mini-USB cables. For this reason, it's important to ensure that your scales are the new variant. The picture below shows the incompatible old iGaging scale (top) next to the new Shahe scale(bottom).

iGaging DigiMag (top) next to Shahe 5403-xxxA (bottom) display

The firmware supports the same set of scales as the TouchDRO Adapter for iGaging scales, but connecting iGaging scales to it will require making a custom USB cable or adapter. Unfortunately, Shahe scales use the "Id" pin that is generally unused in Mini-USB cables, so you will need to use a hard-to-find five-conductor Mini-USB cable and solder splice it to the existing cable to remap the pins.

Pin Functions

Scale Inputs

The adapter supports up to four scale inputs which are connected directly to the MSP430 GPIO pins. During the boot-up, the firmware executes the protocol detection routine by configuring the pins in a particular way and listening for input. If no known protocol is detected, the input will be turned off and data for that axis will not be sent to the application.

Please note, during protocol detection, the clock pins output 21-bit clock signal for iGaging EZ-View scales. This might damaged any scales that are not 3V-tolerant such as some Shahe dial indicators and calipers.

Tachometer Input

Tachometer input is connected directly to the MSP430 GPIO pin and is pulled down to the ground internally and can be used with any sensor with 3V sourcing signal.

Touch Probe Input

Touch probe input is connected directly to the MSP430 GPIO pin and is pulled down to the ground internally. It can be used with any on-off type probe, either normally open or normally closed (the firmware will detect the type at startup)

Mechanical Dimensions

Conclusion

As you can see, the new board is very similar to the existing TouchDRO Adapter for iGaging scales with only a few minor differences. This means that it's running the well-tested version of TouchDRO firmware that is optimized to squeeze maximum performance and reliability from these capacitive scales. As a result, people who chose to build a DRO using these Shahe scales now have an easy-to-use DRO adapter that doesn't require any further assembly or modifications.

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