Building an interface for DRO scales

Quite some time ago I bought iGaging scales for my lathe and small horizontal mill. To make the most of these I protyped a small board with an Arduino Mini and a Bluetooth transceiver. This got mounted in a case, and was swapped between the mill and lathe as needed. Not wanting to point-to-point wire another one I drew up the schematic in DipTrace and ordered 10 boards from

A few weeks later 10 arrived in a shrink wrap package. I built the first one with parts from the prototype, and it works great.

The basis for the project is Yuriy’s TouchDRO app for Android. Freely available it provides a lot of functionality. 4 Axis, Tachometer and Probe inputs are supported. For vertical mills it provides tools for bolt circles, hole patterns etc. While the app has not been updated in some time, we are waiting to see the new features once his workload decreases.

What you need:

Stereo Connector
Arduino Mini 5V
3.3V converter

There is nothing particularly difficult to solder. I suggest to solder the header pins that come with the Arduino mini to the Arduino first, then solder that assembly to the PCB. Add the 1k/2k or 220/330 resistors at R1 (2k/3300) and R2 (1k/220). Solder in the HC05 Bluetooth module as well.

Solder on the USB connector boards. At this point you should wire up your power supply. The preferred module provides 5V and 3.3V but apparently those are now not always available. There is enough space in the top LH of the board to mount a 110->5V supply and a separate 5V->3.3V convertor. Check that you are getting 3.3V at the VDD pin on USB adapter board.

Program the Arduino Mini with the firmware using the standard methods for this operation. There are pins on the end of the Arduino Mini board that match those of typical USB-Serial cables for programming.

finished board

Install the TouchDRO app on your Android tablet. Power up the board and from Settings on TouchDRO connect to the Bluetooth transceiver. This will show up as a series of numbers in the list of devices. Connect one of your scales and verify that the display changes values as you move the scale head. If you are having difficulty at this point, the forum at Yuriy’s Toys has helpful people, and previous posts as well as a resource.

Mark the project box for a cutout to match the Mini USB connectors and cut it open. Add 2 holes for the Tach and Probe connectors on the side. You can use M3 screws to hold the board in the case.

If you find that your readings on one or more axes jumps when you turn on the spindle motor, isolate the scales from machine frame. Spikes will travel along the frame to the scale, and as they are capacitive will result in bizarre readings. Also keep your scales dry from coolant and oil. That too will result in misreading. Thank you to one of our HMEC members for the grounding recommendation.

In use on a small horizontal mill

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