Shahe 5403 and 5204 Digital Linear DRO Scales Overview

For several years the so-called "remote DRO" capacitive scales, manufactured by Wenzhou Sanhe Measuring Instrument Co.,Ltd. have been the mainstay of budget do-it-yourself DRO setups. These scales first appeared in the USA around 2011 under iGaging brand as "DigiMag Remote DRO" or "DigiMag" but then started showing up all over the internet under various brand names, including AccuRemote, Shars and unbranded generic version. A few years ago iGaging has redesigned the display of the scales and rebranded them as EZ-View DRO. Around the same time Shanhe introduced two new models of the Remote DRO scales that look rather similar to the original model but have several key differences.

A few months ago I ordered a couple different lengths of each scale in order to test and reverse engineer the communication protocol, and finally was able to get to it over the holiday break. In short, these scales would work very well for a budget DRO build, but require different firmware to decode the position. As I'm working on adding the support to the firmware, let's take a closer look at the data format these scales use and other important characteristics.

Connecting iGaging Scales to TouchDRO Controller

If you read some of the earlier posts on this blog you will quickly see that the times were much simpler four years ago when it comes to iGaging scales: there was only one kind and red wire was "Vcc", black wire was "Ground", and so on. Since then iGaging has gone through several revisions of the original DIgiMag scales and has introduced AbsoluteDRO and EZ View scales. My goal for this post is to explain what are the different iGaging (and generic scales made by Shahe) that TouchDRO supports and how to connect them to the BlueTooth DRO controller.

TouchDRO Adapter for Glass and Magnetic DRO Scales

TouchDRO adapter for Glass and Magnetic DRO Scales is used to interface glass and magnetic scales that use standard quadrature encoders to the TouchDRO Android application. It supports up to four scale inputs, directional tachometer, and touch probe input. All inputs are buffered and 5V-tolerant. Scale inputs can be either single-ended, or differential (for better noise immunity).

Connecting iGaging Absolute Scales to TouchDRO

Recently I posted a mini review of the iGaging Absolute DRO Plus scales that covered the some basic information on the connection scheme, etc. As I mentioned in the last post, the scales use a different communication protocol. Unlike the DigiMag scales, these scales require additional circuit between them and the MSP430 LaunchPad board. As promised, in this post I will provide instructions on how to connect the scales to the MSP430 Launchpad controller.

Working with iGaging Absolute DRO+ Scales

Since their initial release iGaging Absolute DRO Plus scales seem to be gaining momentum. They have a lot going for them, but unfortunately they are incompatible with the original 21-bit iGaging protocol. For some time I've been getting an increasing number of request to add support to the controller firmware, so a few months ago I went ahead and purchased a 6" scale to experiment with. Finally last weekend I added support for these scales to the "Mixed Scales" MSP430 controller firmware. In the first part of this post I will explain what's different about the Absolute DRO+ scales and provide a quick overview of the data protocol; in the second part I'll provide detailed instructions on how to connect them to the MSP430 Launchpad DRO controller.

Selecting Scales for a DRO

When building a DRO the selection of scales is the most critical decision. Touch DRO Android application can work with a number of different scale types, ranging from inexpensive calipers to 1 micron glass scales. In addition to the cost considerations there are technical parameters that you should take into account. In the previous post I explained which parameters really matter in a DRO setup. Now let’s take a look at some of the commonly available scales and see how they stack up.

Selecting Scales for a DRO - Six Parameters that Matter

Things were easy when iGaging "Remote DRO" were the only scales Android DRO supported. Now that it can work with most of the common scales things are becoming a bit more confusing, judging from the number of emails I've been getting lately. With other things being equal, the choice of scales will have the biggest impact on you DRO's performance. There is a number of options, ranging from cheap Chinese calipers to glass scales and other quadrature encoders. Although I can't definitively answer the question "which scales should I use for my DRO setup", in this post I'll try to explain which parameters matter most in a DRO application.

Reliability Issues with iGaging Digital Scales

Many people are wary of digital readout setups that use capacitive scales because such setups tend to be sensitive to electrical interferences. A shop full of motors, fluorescent lights, transformers and other equipment is a noisy environment and when that noise gets into the DRO system it can cause havoc with the readout. The most common symptoms of such issues include random resets and floating position readout. While it appears that all “chinese” scales and calipers are somewhat prone to these issues, the majority of the complaints fall on IGaging Remote Digital Readout scales. Surprisingly the scales themselves are rarely the culprit. In my experience 9 out of 10 problems with the iGaging scales can be traced to the wiring and/or the power supply.

AccuRemote vs. iGaging DigiMag Digital Scale Comparison

12" iGaging AccuRemote next to DigiMag scales

Recently iGaging has introduced a new Stainless Steel model of their “Remote Readout” digital scales. The new “AccuRemote Digital Readout” scales are supposedly much more accurate and robust than the older DigiMag model, making them a good candidate for a hobby DRO setup. I’ve been getting emails from people wondering if these scales are compatible with the TouchDRO application (or more accurately, TouchDRO Bluetooth Controller), but since I don’t yet own a set, I wasn’t able to confirm this. When a fellow machinistweb.com forum member CaveBob graciously offered to lend his set for a few days, I jumped at the opportunity. Since Bob gave me permission to take one of the scale apart I think it will be helpful to do a side-by-side comparison to see if the scales are really that much better.

Harbor Freight Caliper Data Format

Last week I started putting together the new firmware that will allow the MSP430 Launchpad version of the digital readout to read a mix of different scales and calipers. My last post discussed the needed hardware changes and touched on the high-level requirements. With the adapter board build and tested I was able to start investigating the data formats used by the small collection of calipers I was able to put together. Using my trusty Open Logic Sniffer I was able to identify two different protocols. BG Micro Digital Indicator used the 48 bit protocol described in the excellent article "Chinese Scales" by Shumatech. Surprising none of the other calipers used this protocol.

Reading Grizzly iGaging DRO Scales with Arduino

As I'm waiting for the parts for my do-it-yourself Android DRO, I'll start doing some proof-of-concept prototypes with the parts I already have. So, first things first - we need to figure out how to read the Grizzly/iGaging scales. The easiet way to reverse engineer the protocol is to connect a logic analyzer (Open Lgic Sniffer in my case) and see what's happening in the wires. The screenshot below gives a good idea how those things tick (no pun intended).

21 Bit Protocol Capture