Android DRO Mini FAQ #2

Saturday, November 30, 2013

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.

What types of scales can I used with your application?

At this point you can use iGaging Digimag and AccuRemote DRO scales, standard “Chinese” scales, Harbor Freight calipers and quadrature encoders (such as glass scales).

Which firmware should I use?

It depends… Arduino DRO controller is stable, reliable and easy to build, but I’m not planning on adding new features to it. If all you need is four iGaging scales, Arduino is probably the easiest route due to the broad availability of Arduinos. MSP430 iGaging controller, likewise, is stable, reliable, fast, and pin-compatible with the new MSP430 “Mixed Scale” controller. It will be a bit cheaper and easier to put together, and will provide more flexibility in future if you decide to add tachometer to your machine etc. Finally, if you want to use a mix of scales, the only option so far is the MSP430 “Mixed Scale” version of the firmware. At the time of this posting it’s still in early beta (and is split into two different sub-versions, one for glass scales and one for capacitive scales).

Is the application accurate in metric mode?

Yes. “Under the hood” the positions are stored in their native format. I.e. the application keeps tracks of scales “ticks” and converts the position to inches or mm at the user interface level. There is no difference in accuracy between the two modes.

What are the “Click Per Inch” Settings for my scales?

I strongly recommend that you calibrate the scales using a good dial indicator or the dials on your machine, as there is a small amount of “drift” between different units. With that said, a good starting points are: iGaging - 2560, 0.0002”/5um glass scales - 5000, Standard Chinese Scales - 20480, “Harbor Freight” calipers - 254000.

Will you release a Lathe-specific version?

User interface will change based on the selected machine type

No. The next version of the app will support multiple machine types. The UI will change based on the machine type.

Can I use one tablet/phone with multiple machines?

Yes. You can pair a number of controllers with the tablet/phone and switch between them from the app. Additionally, next version of the app will have “preference banks”. In other words you will be able to have (and switch between) separate configurations for up to 6 different machines.

Is it possible to set the cross slide readout to show diameter rather than radius?

Yes. Simply set the corresponding axis CPI to half of what the actual CPI. For example, for iGaging scales you’d set the CPI to 1280 instead of 2560.

Should I use USB or Bluetooth to connect the controller to the tablet?

If at all possible, use Bluetooth. It’s counter-intuitive, but USB is so much more problematic for many different reason. First, due to the way Android’s USB is handled, when an error occurs in the USB-related code the whole tablet might crash. More importantly, the cable creates yet another ground loop that ought to cause problems.

My tablet doesn’t have a built-in Bluetooth transceiver. Can I use a Bluetooth USB dongle instead?

No. Android doesn’t have the necessary drivers to support external Bluetooth modules so you will need to find the drivers, compile your own ROM, flash it to the tablet, etc. At that point USB is a much lesser evil.

Will Bluetooth work reliably in the “noisy” garage?

Yes. Bluetooth uses 2.4 GHz frequency range and not too many things in the garage can create interferences for it. For instance, your car is much noisier, yet Bluetooth headsets (and even Bluetooth-enabled cars are reliably working all over the place).

Isn’t having a tablet in my dirty garage a bad idea?

Not really. Tables are pretty well sealed against dust and dirt. As long as you use a screen protector and don’t drop the tablet, it will live a long and happy life in the garage. I’ve had my BN Nook Color in the garage for over two years and it’s still in “mint” condition. After all, many people have computers [that are much more open] next to their CNC machines with no issues.

Will you add support for a tachometer?

Upcoming release of the Touch DRO app will include RPM display

Yes. It’s coming to the next version of the application; controllers based on MSP430 will definitely support the tachometer, but I don’t have plans to add it to the Arduino version.

Does your application track and report what I’m building in my garage?

No. The application doesn’t talk to the “mothership” at all. The only statistics I’m tracking is how many people downloaded it from the Android Market.

How much will my DRO build cost?

It depends… A controller can be built for between $20 and $60 (US Dollars), depending on the version. The bulk of the cost of the DRO unit will be in the tablet and the scales. Good name-brand 7” tablet will cost $200 or less; scales can range from $100 to $500 (for glass scales).

How much does the application cost?

Nothing. It’s completely free to use, copy, distribute etc. It doesn’t cost anything to install it from the Android Market or from the source code. Moreover all of the source code for this project is licensed under GPL licence.

Will you have Arduino-based version of the “Universal” controller?

No, for several reasons. First, Arduinos (except Mege and Due) don’t have enough external pin interrupts exposed, so the firmware would need to bypass the abstraction layer and be written directly against the Atmega microcontroller. This in itself would open a can of worms for inexperienced users. Second, I simply don’t have enough free time to split it between different branches. At this point I’m concentrating on MSP430 Launchpad and [possibly] one based on ARM Tiva C Launchpad). On the other hand, if someone wants to share their Arduino-based project, I will gladly host the files and the manuals.

Are you planning to have a version for iPad?

No. Porting the app to iPad will require pretty much a complete rewrite and I simply don’t have the free time for it.

Can I install your DRO application on my Windows (or Linux) computer?

No. At least not natively; the app is designed specifically for Android. There is a way you can run it from an emulator but it’s not really worth it.


  1. Hi Yuri, I really like your stuff. I run a small product design studio in San Francisco and am working on a project I could use your expertise on. Do you do consulting? Its a wifi enabled scale that you wear on your body. Needs to connect with a smartphone. I can be contacted at