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DIY bluetooth DRO for my mill

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vtsteam:
A few years ago I started a project building a low cost bluetooth DRO using a mix of inexpensive digital calipers and an IGaging  scale using plans and instructions found on Yuriy's Toys website. It was a pretty complicated project, mainly because the calipers needed a big hand wired adapter board to interface with a small Texas Instruments controller board.

I built and tested the system, but never got around to mounting it on a machine. One of the calipers was unreliable, and I didn't have much more money to invest in the project.

A couple years ago, when the prices came down, I bought 3 IGaging capacitative scale units, intending to use them as-is, but again, never mounted them on a machine. Fast forward to yesterday, while working on the mill I got irritated trying to read the dials in low light and fighting backlash, I decided then and there to build and add a DRO, but this time, to use both the new scales and parts from the old controller project, but without the caliper adapter board.

So I put together this unit. It has the TI processor board, 4 micro USB ports for X, Y, and Z scales and a rotary encoder. The scales have a backup battery of 2 AA cells, which should provide 2500 hours before needing replacement.

The bluetooth connection is provided by an HC-06 breakout board on the right side of the unit. There are two Shotky diodes between the battery and the onboard USB power supply input to prevent battery charging or backfeeding the battery power to the processor board. Batteries only power the scales which draw 17 uamps. A 2200 ufd capacitor maintains the power during transition between usb power source and battery power to the scales. All of this is detailed on the Yuriy's Toys site

For my own preference, I mounted everything on a vectorboard and cut and wired  traces by hand to reduce the number of jumpers. I did keep some jumpers in order to make the system flexible in case I want to change the port assignments and inputs.

I tested it out tonight and it works great with the Igaging scales and an old tablet I have. The Android software for the display is called TouchDRO. It also works with my cell phone.

The first photo below shows the older mixed caliper and scales project while being worked on.

The second photo is the new DRO project which works with the Igaging scales.

PekkaNF:
Pretty nifty :headbang:

You have this arragement: "The scales have a backup battery of 2 AA cells". I supose it is because scales send absolute position serial signal instead of incremental position?

Good work,
Pekka

vtsteam:
Yes Pekka, these IGaging or Shahe type capacitative (inexpensive) DRO scales store absolute position and transmit that. They also have extremely low power consumption.

Apparently the system can also work with magnetic and glass scales, and quadrature encoders and also with Hall effect tach sensors (for lathe speed), but I believe glass scales only provide incremental position changes, like a typical encoder. You would not be able to store a position using these scales with this system during a power outtage without battery backup for the whole processor board.

Here are some screen shots of the TouchDRO application on both a tablet and a phone. The various hole pattern functions are at the bottom of the screen on a tablet and can be scrolled horizontally. On a phone they are arranged vertically, and can be scrolled through for selection that way

My setup uses an older version of the MSP430 board firmware (1.3). I found that the later version, 2.0 did not work with my scales because, I believe that version update stopped providing a clock signal from the microprocesor board (formerly available board on pin 1.7) that the scales need to receive in order to send data back.

Maybe a separate hardware clock pulse could be arranged. I don't know much about that -- it is above my electronics knowledge level.

Screenshots of a few of the various functions available in the TouchDRO application on tablet and phone:

vtsteam:
I just made up a small plywood box to fit the bluetooth DRO.

I was thinking about lining it with aluminum foil as a shield (except at the end where the bluetooth transmitter is), but I think I'll just try it out without first and see how stable it is.

PekkaNF:

--- Quote from: vtsteam on March 30, 2022, 10:09:39 AM ---Yes Pekka, these IGaging or Shahe type capacitative (inexpensive) DRO scales store absolute position and transmit that. They also have extremely low power consumption.

Apparently the system can also work with magnetic and glass scales, and quadrature encoders and also with Hall effect tach sensors (for lathe speed), but I believe glass scales only provide incremental position changes, like a typical encoder. You would not be able to store a position using these scales with this system during a power outtage without battery backup for the whole processor board.


--- End quote ---

I have traditional DRO with magnetic scales. They are the normal incremental position transducers (A/B and index). I never found it difficult to "zero" on manual machine. CNC needs to home or retain the position. On milling machine I center the part and zero to center of the hole or part..or..zero to vice back jaw (touch jaw and move half diameter, then zero). I am not sure if this is right way, but works for me. I'll learn something else when this stops working.

That big screen interface looks really good. My 7-segment display is pretty unintuitive to use on PCD and such. Zeroing, centering and setting cordinates works well.

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