Build Instructions for Voltage Shifter Circuit

Last post covered the design considerations for the Voltage Shifter required for the Mixed Scale DRO Controller. As promised, in this post I will provide detailed build instructions for this circuit. The board is designed to work with up to four scales and has three power rails. One provide 3.3V power supply to the comparators and [potentially] iGaging scales; the other two can be set to any voltage between 1V and about 18V. Although the firmware doesn’t [yet] support glass scales or tachometer input, this board is ready for them.

3"x4" 1200 hole stripboard
with a track cutting tool

Voltage Shifter Circuit for Mixed Scale DRO Controller

In the last post I introduced the new version of DRO controller that is able to read a mix of common digital scales. You might recall that “Mixed Scale” controller uses the same MSP430 Launchpad development kit as the “Basic” version, but requires a bit of extra hardware. Unlike the the iGaging scales, which work quite comfortably with the 3.3 Volt power supply, most other inexpensive capacitive scales use 1.5V (nominal) power supply. This means that their outputs can’t be reliably read by the MSP430 microcontroller. Similarly, glass scales and quadrature encoders use 5V power supply. MSP430’s inputs can tolerate up to 3.6V, so connecting the glass scales directly to the Launchpad will permanently damage the inputs.

Mixed Scale DRO Controller Project Update

Mixed Scale DRO Controller with MSP430 Launchap

So far the DRO controllers I’ve designed have been able to read only the IGaging (Shahe) Remote DRO scales. Lately I’ve been getting an increasing number of requests for a firmware that could read the standard “chinese” linear scales.A few months ago I started working on a new version that would do just that. Although the project is still a bit rough around the edges, I’m pretty sure that the hardware will stay unchanged and any future updates will be done via firmware. Rather than holding off until the whole shebang is done, I decided to post the stable version of the firmware. In the next few posts I will provide details for the project, design considerations, build instructions and firmware implementation.

How To Upload Firmware to MSP430 Launchpad

A few months ago I posted build instructions for a DRO controller that uses MSP430G2553 microcontroller with a TI MSP430 Value Line Launchpad. Compared to the original version that used Arduino, the Launchpad version has a few advantages, such as lower cost and simpler construction. On the other hand, firmware upload process is not as user-friendly as that offered by the Arduino software. Fortunately, you don't need to install the full-blown IDE, list TI Code Composer Studio or even the MSPGCC tool chain. Instead the pre-compiled firmware can be flashed using a free command line MSP430 Flasher tool offered by Texas Instruments.

Android DRO Application Settings

This post refers to the old version of the application. Please refer to TouchDRO Settings Overview for the updated information.

As I mentioned in the last post, the new version of the Android DRO application has a lot of updates. In addition to the new functions there is a plethora of internal changes. Some of the new features are accessible through the “Settings” screen. The good news is that if you intend to use the application with one of the iGaging controllers, the default settings will be sufficient to make it usable out of the box. On the other hand, to take advantage of the new features, you will need to get your hands dirty. In this post I will try to explain what each of the settings does, hopefully making the setup pain-free.

New Version of Android DRO Coming Soon

When I released last version of the Touch DRO application early this year my plan was to have a new version out by April. This, obviously, hasn’t happened due to a number of reasons, including a busy work schedule, a never ending list of things to do around the house etc. On top of that, from the received feedback, I realized that I had to make the “guts” of the DRO application much more robust before the new features can be added. Now, after a fairly major overhaul, the application is getting ready for the release and includes some of the lacking functions.

This version of the DRO is optimized to be used on a milling machines with three or four linear scales but with a few minor tweaks can be adapted to a lathe. Some functions, such as tool offset, will work identically on a lathe DRO.

Three Ways to Improve iGaging DRO Scales Reliability

Shielded USB cables can eliminate most of the noise issues
and costs only a few Dollars

In the last post I covered the root causes of the two most common reliability issues with iGaging digital scales. Although those scales catch a good amount of flack of being unstable when mounted on a machine, the problems are rarely caused by the capacitive transducers. In my experience the problems with random resets and unstable readings can be traced to the wiring and are relatively easy to remedy. The mods described below can be done for under $10 total in less than an hour but can make a huge difference.

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.

Arduino DRO DIY Build Instructions

If you’re planning to build a basic digital readout using iGaging “Remote DRO” scales and the “Touch DRO” Android application, you will need to make a controller that will interface the scales to the tablet. At this point I’ve designed two different version: one is based on Texas Instruments MSP430 LaunchPad and the other uses an Arduino. Both controllers offer the same functionality so the choice comes down to a personal preference and the availability of the microcontroller board. Yesterday I posted build instructions for the Launchpad version. In this post I will provide detailed step-by-step directions for a DRO controller using Arduino UNO and an inexpensive Bluetooth adapter.