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Adapter Board for Shahe and iGaging Capacitive DRO Scales

Monday, February 25, 2019
Capacitive Scale DRO Adapter

TouchDRO adapter for iGaging and Shahe scales is designed to work with several models of 3V capacitive linear DRO scales manufactured by Sanhe Measuring Instrument Co.,Ltd. and distributed under different brand names. It supports up to four linear scales, directional tachometer and a probe or tool height setter input. The circuit is designed and laid to provide reliable operation of capacitive DRO scales and significantly reduce the effect of shop noise and electrical interference on the scales, compared to a do-it-yourself adapter.

TouchDRO Supports new Chinese DRO Scales

Monday, February 4, 2019
TouchDRO "Black" Adapter Support All of The Shown Digital Readout Scales Now 

A few weeks ago, I finally found some time to experiment with the new Shahe Digital Linear Scales 5403-xxx and 5204-xxx. Electrically these scales are compatible with other 3V capacitive DRO scales such as iGaging DigiMag, EZ-View DRO and iGaging Absolute DRO. This means that adding support for the new scales is a matter of updating the firmware of the TouchDRO adapter for iGaging and Shahe DRO scales. After cursory check of scale protocol, I was expecting this to be a relatively easy addition to the existing firmware since they use the familiar BIN6 protocol. In practice, supporting Shahe "Remote DRO" scales ended up requiring a complete rewrite of large portion of the firmware. While at it, I decided to invest some more time into adding several other improvements that have been on my "to do" list for some time now. After several weeks of testing and debugging, the new firmware is ready to be released. In addition to the added protocol support, the updated firmware includes a few major performance and stability tweaks that will make capacitive DRO scales behave much more reliable in a shop environment.

Shahe 5403 and 5204 Digital Linear DRO Scales Overview

Sunday, January 6, 2019

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.

Blu-DRO Now Uses the TouchDRO iGaging DRO Adapter

Monday, January 1, 2018

I get a fair number of emails asking if I sell fully assemble board, in a box, ready to go. Although I have seriously thought about offering a fully turn-key version of the iGaging DRO controller, I couldn't get the numbers to pensil out: the cost of making a custom injection molded enclosure is ridiculously high, and 3D printed enclosures take too much time and I couldn't find a way to make it scale. Meanwhile, I knew that Al at blu-DRO.com has been selling fully enclosed Arduino TouchDRO controllers. I've met Al "virtually" on TouchDRO Bata Testing Google+ community, where he had been a frequent poster, always willing to help or answer questions. Furthermore, the feedback I got from people who purchased blu-DRO units was very positive about his level of customer support, etc. After some "noodling around" I decided to email Al and see if we can find a way to work together. A few emails later we decided that I will sell the boards to Al in bulk at a bit of a discount so he can use them in his units. This seemed to be a win-win situation: Al would get more robust controllers for the blu-DRO and I can stop worrying about creating a turn-key version of TouchDRO.

Virtual Layout Feature Preview

Tuesday, July 4, 2017

In the last post I showed some of the updates coming to the next version of TouchDRO. The new version will include a lot of tweaks, UI changes and improvements aimed to make the DRO even more flexible and efficient to use. As is, TouchDRO can already do much more than and old-school DRO, but next version is getting a number features that will push the limits of what you can do with a non-CNC mill or lathe. One of those features is the ability to set a background image in layout view and use the mill or the lathe to trace the contour.

Sneak Peek of the New TouchDRO Version

Monday, July 3, 2017

It's been awhile since the last major TouchDRO version release and I'm getting an increasing number of emails asking if I'm still developing the app. The answer is "definitely yes", and the new version is getting very close to be ready for beta testing. It has a number of new features and countless quality-of-life changes. I've been testing it in my shop for some time now and most of the functionality is pretty stable so it's a good time to post a quick preview of some of those changes and new features.

SIEG X2 Mini Mill CNC Build - Component Selection

Monday, May 1, 2017
Set of castings for SIEG X2 CNC Mill

In the last post I outlined my plan for building a CNC mini mill from a set of SIEG X2 castings. As the first step I wanted to order the parts for the mill itself, ignoring the steppers, controllers, etc. and make sure that I can get it up to snuff. There is no set budget for this project, so the choice of the parts is mostly based on availability (and common sense). The two areas I wanted to concentrate on are spindle accuracy and overall repeatability. With that in mind, in this post I will explain what parts I chose to buy and why.

SIEG X2 Mini Mill CNC Build - Introduction

Sunday, April 9, 2017
Some of you might remember that several years ago I used to own a Harbor Freight Mini Mill, AKA SIEG X2. At one point I upgraded the X-Y table to the LMS large table assembly and the old small table has been collecting dust under my workbench. I couldn't force myself to throw it away but couldn't find a use for it either. Until a few weeks ago, that is, until I stumbled across a series of three videos by Stefan Gotteswinter in which he rebuilds a Chinese angle plate. In the introduction to the first video he explains that he bought it as a "set of castings" and proceeds to completely re-machine the whole thing. This gave me an idea...

Connecting iGaging Scales to TouchDRO Controller

Sunday, December 4, 2016

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.

Choosing the Right TouchDRO Adapter for Your Scales

Tuesday, September 27, 2016

One of the main design goals for the TouchDRO project was to create a flexible modular do-it-yourself digital readout for hobbyists and makers alike. Since raw scale position decoding happens in the adapter, one of the first decisions when setting up a TouchDRO system is the selection of the adapter. At the time of this writing there are two versions of pre-made adapter board and four different do-it-yourself options. All those choices can be confusing if you're new to the TouchDRO ecosystem, so let's look at the benefits and tradeoffs of each of the six options.

UPDATE: February 24, 2019 - the original content of this post has been updated to reflect the currently available adapter board choices and firmware versions.

Licensing and Legal Stuff

Before digging deeper into the adapter options, let's cover some legal stuff. TouchDRO is a free application and I provide several free versions of the adapter firmware. The app is distributed via Google Play Store and is free for personal or commercial use, subject to Google Play Terms of Service. Free versions of the firmware are free for personal use only. In other words, for personal use you can choose between the pre-made boards or a DIY approach using one of the free firmware versions; for commercial use you can't use free firmware and need to buy a premade board.

Building vs. Buying a TouchDRO Adapter

The main factors in deciding between getting a pre-made board or scratch-building a DRO adapter will likely come down to your budget and comfort level with soldering, firmware flashing and troubleshooting. Scratch-building a DRO adapter can be less expensive, costing between half and one third of the pre-assembled adapter price. A ready-to-go adaper board is less hassle, on the other hand.

Pre-Made TouchDRO Adapter

Pre-assembled TouchDRO adapters are a better choice for people who need good reliability and people who aren't proficient with electronics. Even for those who have good soldering skills and equipment the pre-made boards have a few important benefits:

  • Pre-made boards use purpose-designed printed circuit boards that are laid out to minimize noise and electromagnetic interference, so they perform much better in the shop environment. This is especially true for the capacitive scales. A lot of people who built do-it-yourself have issues with random scale resets and position jumps due to noise and interference. These problems are virtually non-existent with the premade boards.
  • The firmware used by the pre-made boards has a number of tweaks and optimizations that are not included in the free version. For instance, the firmware that ships with the iGaging and Shahe DRO Adapter has more advanced tachometer implementation, adaptive scale refresh rate and supports mixing and matching of five different types of 3V capacitive DRO scales.
  • The board are professionally assembled using quality printed circuit boards, name-brand components, including Panasonic electrolytic capacitors, Texas Instruments ICs, and are inspected to pass IPC-A-610 Class 3* workmanship standard. This ensures long service life, low failure rate and excellent reliability.
  • Before shipping an order I personally inspect every board and run it through a comprehensive testing routine. This means that when you receive the adapter board you ordered you won't have to waste your time troubleshooting soldering issues, part defects, etc.

* IPC-A-610 Class 3 is usually required for medical devices, aerospace equipment etc. Good quality industrial equipment generally uses Class 2, so Class 3 a big step up in this case. You can read more about Class 2 vs. Class 3 here.

Scratch Built Do-It-Yourself DRO Adapter

As mentioned earlier, scratch-building a DRO adapter is significantly less expensive. On the low-end, a basic adapter for iGaging DigiMag and EZ-View DRO scales (i.e. scales that use the 21-bit protocol) can cost under $20 using MSP430 LaunchPad board and a HC-05 BlueTooth transceiver. Do-it-yourself adapters for glass/magnetic or 1.5V DRO scales will require significantly more parts and a prototyping board, and will likely cost around $50.

Another good candidate for a do-it-yourself DRO controller is a setup that uses 1.5V scales or a mix of 1.5V and 3V scales. There is no ready-made TouchDRO board that can interface with 1.5V scales, so scratch-building a buffer circuit. Please refer to Build Instructions for Voltage Shifter Circuit for more details.

Do-it-yourself DRO adapters can suffer from a few problems when used with capacitive scales. The reason being that capacitive scales are very sensitive to line noise and benefit greatly from good PCB layout with ground fill and properly located bypass capacitors, which is hard to do when using a breadboard. Glass scales are generally not affected by the PCB layout as much and work very well with DIY DRO setups. The only minor downside is that proper differential line drivers are not available in through-hole packages, so building an adapter for scales that use RS-422 (TIA/EIA-422) is much more tricky and somewhat more expensive.

Adapter for Glass and Magnetic Scales

Vast majority of the modern Glass and Magnetic DRO Scales use quadrature output, which is supported by the TouchDRO Adapter for Glass Scales board as well as the MSP430 LaunchPad Quadrature DIY DRO Adapter. The difference between the free firmware and the version that comes pre-installed in the adapter board are pretty minimal. The main advantage that the pre-made board offers is the use of a purpose-designed differential quadrature input driver IC. This is important for two reasons. First, many of the scales have very strict impedance and back EMF requirements. Pushing the scales too far out of their designed envelope can lead to shortened scale life or even damage. Second, the decoder chips can handle much faster signal rates (on the order of 32 MHz per channel).

Unfortunately there is no scratch-built equivalent of this board since the ICs used for the differential signal decoding aren't available in through-hole package. A DIY adapter using a comparator or a simple buffer is usually adequate but is far from ideal for those scales.

Tip: The best way to determine if the particular scales you have or are planning to purchase are compatible with TouchDRO is to refer to the scale's specifications sheet. Ideally there should be a drawing that shows the output signal that looks similar to one of the drawings below. Otherwise, if the scale is advertised to output RS-422, EIA-422-A or something similar, the scale outputs differential signal. Otherwise, if it mentions TTL, it's likely that the scale outputs single-ended quadrature signal. Another clue might be provided by the pin function diagram. You should see pins marked A, B, Z, R, 0V, +5V, Ground, Shield, etc. For differential scales you might also see A-, B-, A', B', etc. If that is the case, the scales will be compatible with the Quadrature controller. On the other hand if you find pins market "Clock", "Data" or similar, the scale is almost certainly incompatible.

Adapter for 3V Shahe and iGaging DRO Scales

There are three families of 3V "Remote DRO" scales sold by Shahe, iGaging and a few other manufacturers. Scales like the original iGaging DigiMag "Remote DRO", iGaging EZ-View DRO Plus, AccuRemote Digital Remote Readout and Shars "Digital Machine Aluminum/Stainless Steel Scale" use proprietary 21-bit data format. iGaging Absolute DRO Plus scales use a modified version of Mitutoyo protocols. Finally, the newer Shahe "Round Head" and "Square Head" Linear DRO scales use a format similar to the cheap Chinese calipers.

Scales that use the 21-bit protocol are fully supported by the MSP430 LaunchPad Basic DRO Adapter while the Adapter Board for Shahe and iGaging Capacitive DRO Scales supports all three scale families as of firmware version 2.0.

In addition to supporting more scale protocols, the Adapter Board for Shahe and iGaging Capacitive DRO Scales comes with optimized firmware that offers better stability and faster position refresh rate. More importantly, due to more optimal PCB layout and liberal sprinkling of bypass capacitors the board is a lot less prone to EMF and other shop noise.

Adapter For 1.5V Scales

The only way to interface 1.5V scales, such as the old-style Chinese linear scales with integrated display or digital calipers is to build a 1.5V to 3V buffer circuit similar to the one described in the Build Instructions for a DIY Voltage Shifter Circuit post and use the "Mixed Scale" firmware. Currently the firmware supports Sylvac 48-bit protocol, BIN6 protocol and 21-bit iGaging protocol.

Summary

If you are looking for a budget friendly DRO for personal use, enjoy building things from scratch, know how to solder and upload the firmware to a microcontroller, and have the tools (and patience) to troubleshoot noise issues, then scratch building a controller is an obvious choice. Please refer to the Do-it-Yourself DRO Scale Controllers Overview for more details.

On the other hand, if you're not comfortable with electronics, buying a pre-made board provide much less frustrating experience.

If you fall somewhere in the middle, here are my recommendations:

For iGaging and Shahe 3V scales I would strongly suggest getting the pre-made TouchDRO Adapter for Shahe and iGaging scales. If you browse the site you'll see many comments from people having problems with iGaging scales related to the noise that can be very frustrating to track down and fix. Pre-made iGaging controller is much more resilient and handles the noise very well. For other capacitive scales you will need a voltage shifter circuit.

For quadrature scales the choice of the controller is a bit less clear cut: the DIY voltage shifter circuit will work good enough for most modern 5 micron glass scales. I've used it on my milling machines for a couple of years without any ill effects and was pretty happy with the performance. On the other hand, there are scales on the market that have very particular input circuit requirements and can be easily damaged otherwise. Many of the magnetic scales, for instance, fall into this category. For such scales the pre-made TouchDRO Quadrature Adapter is a safer choice. Moreover, for setups using 1 micron scales I would opt for the pre-made controller as well, since it can handle faster signal rates better.