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Build Instructions for Voltage Shifter Circuit

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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
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Finishing the Voltage Shifter for Mixed Scale DRO

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A few weeks ago I posted the build instructions for an adapter board that can be used for interfacing various digital scales to the MSP430 Launchpad DRO controller. Following those instructions you will end up with a base adapter board that still needs to be configured for your particular setup. This includes providing each scale with an appropriate power supply voltage, hooking them up to the corresponding “virtual ground”, and connecting the adapter to the MSP430 Launchpad. In this post I will use the DRO unit I built for my own mill as an example of a mixed-scale setup.

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Mixed Scale Controller Firmware Posted

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Recently I've been working on a new version of a DRO controller that will be able to read a combination of different scales. Although the project is taking much more time than I anticipated, I’m making steady [but slow] progress. Last week I had some free time, so I was finally able to button-up some stability issues with the common “Chinese” scales. Unfortunately I still haven’t finished a truly universal version, so you won’t be able to mix glass and capacitive linear scales (yet). Never the less I posted two versions of the firmware: one that read up to four scales and one that reads the common capacitive linear scales. Links to both versions are posted on the DRO Project Downloads Page.

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Android DRO Mini FAQ #2

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As the interest in the Android DRO project grows, so does the number of questions I get each day. Some of those questions keep coming up regularly, and since it’s been almost a year since I posted the “Android Digital Readout Micro FAQ”, it’s time to post another one. This post will not cover every question you might have, but hopefully it will address most of the common ones.

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Selcting Scales for a DRO - Six Paramenters that Matter

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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.

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Selecting Scales for a DRO

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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.

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Adding DRO to my Grizzly G0463 (Sieg X3 Mill)

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Several people asked me to post pictures of my DRO setup. Today I started installing a new DRO unit on my Grizzly G0463 (A.K.A. Grizzly Small Mill/Drill or Sieg X3) mill and decided to take advantage of this opportunity to take some pictures and post the progress.

I’ve been itching to get a set of glass DRO scales for a while but the cost has kept me off. Last July I randomly emailed a seller on eBay and asked if they would happen to have a returned or blemished unit they’d sell to me for experimenting. Surprisingly the guy replied that he is discontinuing the Easson scales and has two units [8” and 16”] that he’d sell at a steep discount. Additionally, he had one with a broken reading head that he’d throw in if I wanted it for parts. He wanted $200 for all three of the scales, including shipping. Needless to say, I jumped at the opportunity. When the scales came, I took the broken unit apart to see what’s inside and right off the bat found the problem. The Vcc line was broken and the exposed wire was shorting to the case. Five minutes later I had three working scales: one 8” long, and two 16”.

 
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New DRO for my Sieg X3 Mill Finished

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In the last post I started covering the installation of the glass scales on my Grizzly G0463 (AKA Sieg X3) mill. You might recall that I got the scales loosely mounted on the mill but didn’t have a controller to use them with. I didn’t want to tie-up the unit I’ve been using for testing, so before going any further I had to build a new one. This weekend I got some free time to finally build the controller and [mostly] button thing up.

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DRO Project Roadmap for Early 2014

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Well, first of all, Happy New Year! I hope 2014 will be a great year for everyone. There is a lot of stuff in the pipeline for the Android DRO project for the 2014, including a new version of the TouchDRO application, new MSP430 Launchpad controller firmware and better documentation among other things. Now that I’m back from the holiday vacation, I’m ready to start tackling my “to-do” list.

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Connecting Glass DRO Scales to The Controller

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After the two posts describing the DRO setup for my Sieg X3 mill, I’ve received a ton of emails asking for more details. It appears that a number of people are having issues with the glass scales. Additionally, there has been a lot of interest in the simplified version of the interface board. I think a more detailed follow up is in order.

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DRO Interface Pin Functions for MSP430 LaunchPad

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Last week, after posting the “Roadmap for the DRO project”, I received a few emails from different people who were working on developing a custom PCB for the controller that can use the firmware I created. During one of the conversations it dawned on me that I never explained what my intentions for the Launchpad Interface are. At this point a lot of the controller functionality is still “vaporware” (i.e. I’m still working on it). Fortunately, when selecting the platform for the DRO controller I planned out the connections. I wanted to be sure that MSP430G2553 that come with the “Value Line” LaunchPad kit, so I carefully mapped out the future needs. In this post I will try to explain how the pins are currently used, and which pins will be used for future expansion.

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TouchDRO Coordinate System

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DRO Coordinate System

One of the aspects of the TouchDRO application that causes confusion is the coordinate system. Every once in a while I get questions like “Can I do hole circle/pattern/tool offset on a different plane because on my mill the spindle is X (or Y) axis?”, or something along these lines. This question really means that the DRO is not set up right and the user is trying to compensate for it by “customizing” the user interface. Obviously, this is your DRO and you are free to set it up whichever way you like it. TouchDRO is pretty flexible, and the basic DRO functionality will work just fine even if you have axes mixed up and backwards. After a while you will likely get accustomed to it, and use the DRO without second thoughts. Never the less following the conventions is a good idea in the long term.

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Battery Backup For DRO Interface

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In the first part of the build instructions for the MSP430G2 LaunchPad-based DRO controller I showed a few pictures of the unit I built for my mini mill. Out of necessity my controller had to have battery backup, since the power in my garage was very flaky and the circuit breaker tripped every time I looked at it crooked. The battery backup circuit I built originally was a quick stop-gap measure that would get me through until the garage was rewired properly. I didn't spend much time designing that circuit. Since several people asked me to provide more details about it, I decided to take a more methodical approach for this post.

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Beta Version of TouchDRO Now Available

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Yesterday I published the first beta build of the TouchDRO application to the Google Play Store. This release includes a few major upgrades, such as tool library, tachometer, configurable user interface and preference banks. Tachometer output is pretty much self-explanatory; the other three need a bit more clarification.

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More New Features in TouchDRO

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About a week ago I started posting nightly builds of the new release of TouchDRO application. Based on the feedback provided by the beta-testers I've made a few changes to the user interface. The biggest one is the addition of the new "Axis Details" screen. It's purpose is to display the feed rate and chip load while the axis is moving, and offer few axis-specific functions.

Clicking the axis readout brings up the "Axis Details" view
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Axis Details Dialog

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Axis Details Dialog
Axis details view is accessed by briefly pressing a linear axis readout while the DRO is in "Connected" state (readout text appears green). The view is intended to provide access to several axis-specific functions, as well as real-time feed rate and chip load displays.

Position Display

Displays the current position, taking into account currently selected units and coordinate system (absolute or incremental).
When touched, brings up the "Set Axis Dimension" function.

Feed Rate Display

Displays the current feed rate when the axis is moving. The value can be either positive or negative, depending on the direction of the motion. The value is refreshed at 2Hz frequency (two times per second) regardless of the velocity.

Chip Load Display

Chip Load display in enabled state (axis not moving)
Displays the chip load when the axis in moving and a tool is selected. The value is calculated by dividing the freed rate by the product of RPM* and tooth count.
When no tool is selected and/or the tachometer is disabled, the display will be disabled and a toast will briefly appear informing the user that one of the above requirements is not met.
Chip Load display in disabled state
*Setups that don’t include a tachometer can still take advantage of this function by entering the RPM directly using the "Set RPM" function.

"½" Function (AKA "Centerline")

Sets the incremental zero to the position exactly 1/2 way between the current incremental zero and the currently displayed dimension. The most common application of this function is to find center of a hole or another feature.

"+/-" Function

Inverts the current dimension. I.e. multiplies it by -1, so positive dimensions become negative and vice versa. This function can be used to move to a position that is at the same distance on the other side of the zero point. In other words, to machine symmetrical features.

Zero Set

Identical to the similar function on the main DRO screen, but acts upon the selected axis.
Short pressing the button sets incremental origin for the selected axis to the current position.
Long pressing the button sets the workpiece origin for the selected axis to the current point.

Audible Alert

Toggles audible "near zero" alert for the current axis on and off.
When on, the DRO will emit series of beeps starting at 0.250" (10mm when in metric mode). At 0.100"/5mm, 0.010"/2.5mm and 0.005"/0.1mm the frequency of beeps increases. When the axis moves to within 0.001"/0.05mm of 0.000, the application will emit one 2-second long beep and stop.
Audible alert button in "off" and "on" states
The alert is in effect as long as the dialog is open. When the dialog is dismissed, the alert will be turned off.

DRO Scale Calibration

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I’ve received a fair number of complaints about the readout being inaccurate when the default counts-per-inch were used. These problem can be caused by several different issues. First of all, CPI for most of the the capacitive scales isn’t officially provided by the scale manufacturers. The values for many of the commonly available scales have been found experimentally, and might be off by one or two counts. In addition, there are manufacturing tolerances, rounding issues etc, that can skew the numbers even more. Furthermore, many of the scales that come from China are metric. For instance, the glass scales that are advertised to have resolution of 0.0002” have resolution of 0.005mm, and 5 microns don’t equal 2 ten thousands. This leads to an error in CPI. Based on the 0.0002” resolution the CPI should be 5000, but in fact it’s 5080, which is almost 2% off.

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TouchDRO Initial Setup

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TouchDRO is designed to work with a wide range of scales and machines, but it will not work right out of the box. After the application is installed, it needs to configured to match your particular setup. The process isn’t complicated and takes just a few minutes, though.

By default the application is configured for a three-axis vertical milling machine that uses imperial units. If that matches your setup, the only thing you’ll need to do is to configure your scales and the DRO will be good to go. Otherwise, there are a few additional settings that needs to be changed.

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TouchDRO Settings Overview

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By default TouchDRO is configured for a 3-axis vertical milling machine, but the configuration can be easily changed using the "DRO Settings" screen. The screen can be accessed through the context menu, using the "Setting" option.

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Android DRO Step By Step Overview

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Since I added a DRO to my mill I can't imagine how I lived without one for so long; it makes working on the mill so much easier and more efficie. Since you're reading this post, you are probably looking into building a DRO as well, and if you feel lost, you're not alone. Although I've been trying hard to keep the project as simple as possible, so it remain accessible to people with little or no experience with electronics or computers, it might seem a bit overwhelming.I this post I will provide a quick summary of the steps needed to get a DRO up and running with links to more information where appropriate.

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