Introduction to TouchDRO System

TouchDRO is a do-it-yourself DRO project for hobbyists, makers, machine shop enthusiasts, and small prototyping shops alike. It provides all of the key functionality of a traditional DRO unit but is more powerful, versatile, and easy to use. Being a software-based system, TouchDRO is completely different from a traditional DRO unit and, at first glance, might be confusing to some people. If you are planning to build a DIY digital readout, this article will help you better understand the building blocks of a TouchDRO setup and how it differs from a traditional DRO.

TouchDRO vs. Traditional DRO

Traditional digital readouts use purpose-built proprietary displays that are compatible with a particular scale model. Inexpensive units rely on simple 7-segment displays for position readout; more expensive DROs incorporate a monochrome LCD display. Only the top-of-the shelf models offer a color display with resistive touch capability.

In contrast, TouchDRO is an Android application that runs on commodity Android hardware. Since virtually all Android tablets and phones now come with a high-resolution multi-touch color display, TouchDRO's touch-based graphical user interface is not constrained by a physical keypad and a 7-segment display or a small LCD display. Moreover, even a modest Android tablet offers factors of magnitude more processing power and storage than the microcontroller in the most advanced traditional DRO units. As a result, TouchDRO can offer versatility, functionality, and features that are not available even on the high-end DRO units.

Architecture Overview

A TouchDRO-based DRO system requires three components to function: a set of position encoders (DRO scales), an Android device running the TouchDRO app, and a wireless scale adapter that lets the app get data from the scales. The fact that the system is not monolithic makes it much more flexible. On the other hand, there are more choices to make. To help you better understand what's involved in putting together a DIY TouchDRO digital readout, let's look at each component separately.

TouchDRO Application

TouchDRO is a free Android application that runs on most modern Android phones, tablets, and even some Chromebooks. It can be installed from the Google Play Store free of charge or ads. Once installed, the app can be configured to suit your particular needs. Things like machine type, number of readouts, tachometer display, readout precision, and other parameters are easily configurable from within the application with just a few clicks. The settings are organized into "configuration banks" that can be switched with one click, so a single tablet can be used with multiple machines or machine configurations.

The current version of the TouchDRO application has very modest system requirements. It works very well on a 7" tablet running Android OS 4.0 or later and truly shines on a 10" or larger tablet running a more recent OS version.

Position Encoders

Quite obviously, a digital readout system requires a set of position encoders to measure the position of the cutting tool in relation to the workpiece. Therefore, when building a DIY digital readout, the most important decision is the type of scales the DRO will use.

The majority of mainstream commercial DROs use glass or magnetic scales since the scales offer good balance of cost, reliability, and resolution. As Chinese glass DRO scales have come down in price, they are becoming more common in hobby setups. That said, budget-conscious hobbyists still favor capacitive scales for their do-it-yourself DROs. Although these scales have some tradeoffs, they cost half as much as the cheapest glass scales and work well enough for smaller hobby machines. Finally, for some special conditions, a do-it-yourself DRO might use a rotary encoder in some sort of rack-and-pinion setup or coupled to a lead screw.

TouchDRO supports most modern glass and magnetic scales that output 5V quadrature signals and an overwhelming majority of common capacitive scales. When choosing the DRO scales, there are some important factors to consider besides the price. You can read more about this on the Understanding DRO Scale Parameters page. If you decide to go with capacitive scales, please take a look at the list of Compatible Capacitive DRO Scales to make sure that your scales are supported.

TouchDRO Scale Adapter

A TouchDRO adapter is a digital interface circuit whose job is to condition and decode the signal from the scales, convert it into a standard format, and transmit to the application via BlueTooth. Although it doesn't look like one, a TouchDRO adapter is basically a small purpose-built computer that runs a custom piece of embedded software to do all the necessary processing. There are a few different versions of the firmware that can be loaded into the adapter to make it work with various types of scales. The combination of the firmware and input conditioning circuit determines which types of scales an adapter will support.

Scale adapter circuit is intentionally designed to be easy to scratch-build. It is based on Texas Instruments Value Line MSP430 Launchpad and uses readily available components. Required firmware is available as a free download from the Downloads page. Total build time is usually no more than a few hours.

Alternatively, the most common adapter configurations can be purchased as fully assembled, programmed, and tested board from the TouchDRO store. Functionally, the DIY circuit is no different from the equivalent pre-built version, so the tradeoff is between cost and convenience. I.e. a pre-made adapter costs two-to-three times more than a scratch-built one, but all of the assembly, programming, and testing is done for you.

Summary

TouchDRO provides an easy way to build a powerful DRO that offers features of a top-shelf digital readout at a fraction of the cost. Thanks to its modular architecture and touch-based graphical user interface, TouchDRO is an extremely versatile system that can be adapted to work with numerous scale types and many different machine configurations. Since the application and scale adapter firmware are available free of charge, it's possible to build a TouchDRO based digital readout from commonly available components very inexpensively. Alternatively, a few of the common adapter configurations are offered as fully assembled boards.