TouchDRO on a mini lathe

[modeldozer]

Have bought two digital readouts a few years back, with the intention to fit them to my mini lathe.  As they have fairly small displays it would be quite tricky to mount them in a safe place and still be able to read them, so ever since have been investigating a suitable display.

Searching the web for information on the protocol used by these scales to communicate, I stumbled on TouchDRO by Yuriy Krushelnytskiy on his site http://www.yuriystoys.com/

He is using a tablet as the display, communicating via Bluetooth with a controller that reads the scales.

The controller consists of a microcontroller and voltage level shifters to “translate” the scale voltage levels to that of the microcontroller.
Ordered the MSP430 Launchpad from TI and developed a suitable PCB for the controller.  The PCB was made as universal as possible allowing for any scale voltage and internal or external clocking on each channel, selectable by jumpers.



Opted for USB B style connectors as this made the cabling easier.  Originally I wanted to incorporate the option for sub-D connectors for glass scales, but there do not seem to be a standard pin out between different makes, so I included the option for pin headers that could be wired to sub-D connectors.
Voltage regulators are also onboard so single 7V to 25V DC supply can be used, or for a regulated 5V supply the onboard 5V regulator can be omitted and a link fitted.





The PCB was made using positive pre sensitized board.



The holes were drilled on my CNC router.



Populating the board.





And fitted in a case.





Cables was soldered to the scale boards and a decoupling capacitor soldered across the supply.



Testing the system.





The scale for the Z-axis was mounted at the front below the apron in such a way that a cover could be fitted over it to protect against dirt entry.





The X-axis was a bit more difficult and I had to loose some clearance at the rear of the saddle.




A support was also made for the tablet.




Had to replace my original tablet as it did not support the correct Bluetooth protocol but ever since I am very happy with the unit.

Many thanks to Yuriy for his ongoing effort on a great invention.

Cheers
Abraham

[awemawson]

  A very niffty project 

I can see all sorts of uses for that sort of set up.Did you have to modify 'app' for the tablet or is is as per yuri?

I'm slightly puzzled what happened to the 'Y' display in the later tab let screen shots ?

[modeldozer]

Hi Andrew,
No i did not write the app it is the work of yuriy as mentioned.

The app is configurable and in lathe mode the Y can be disabbled.

Abraham

[John Rudd]

Nicely done, I like the pcb you made...

What software did you use for the board?

[modeldozer]

Hi John,

I used Eagle for the board with the pcb-gcode ulp for the drilling.

Abraham

[vtsteam]

Wow! 

[krv3000]

thats just showing off  just brill

[Arbalist]

Although I don't strictly need a DRO on my mill I'd like one. Having looked at the options it was too expensive for me, the display being the single most expensive item. I hope someone comes out with a reliable off the shelf solution that uses a tablet. Will this system work with magnetic scales? I'd rather pay the slight premium for a more robust scale.

[backofanenvelope]

Just wanted to add my for this project. Very neat.

TomC

[philf]

Although I don't strictly need a DRO on my mill I'd like one. Having looked at the options it was too expensive for me, the display being the single most expensive item. I hope someone comes out with a reliable off the shelf solution that uses a tablet. Will this system work with magnetic scales? I'd rather pay the slight premium for a more robust scale.

Have a look at http://www.yuriystoys.com/p/android-dro.html

To quote: "Quadrature controller is 100% pin-compatible with the Mixed Scale version, but uses firmware optimized for quadrature encoders, including 1 micron magnetic and glass DRO scales."

So the answer is yes.

Phil.

[Arbalist]

Thanks Phil.

[CrazyModder]

Although I don't strictly need a DRO on my mill I'd like one. Having looked at the options it was too expensive for me, the display being the single most expensive item. I hope someone comes out with a reliable off the shelf solution that uses a tablet. Will this system work with magnetic scales? I'd rather pay the slight premium for a more robust scale.

Same here. I'm in the process of making myself a DRO (for a few years now, you know how it is...  ). I did make a 3-axis 7-segment-display years ago (before the advent of cheap tablets ) which has all the electronics to connect the cheap chinese scales. I even have a bluetooth chip and some arduinos lying around, and am willing and able to hook them up. Still missing the scales though. I experimented with sawed-off ultra-cheap scales (in the 10€ range) as prototype, but that did not go well at all as they are much to fickle to work in a dirty environment.

I have been procrastinating about getting "real" scales and will probably go for it soon[tm]. It will likely be a kit with proper mounting options, so that at least is taken care of.

Unfortunately, glass or magnetic scales do not come with a "slight premium" for me, they cost around 10 times as much as the capacitor style "chinese" scales. A set of those, made for the mill, cost roughly 110,- €; the cheapest glass or magnetic set is almost 1000,- € at my sources. I assume that is because there is probably not a market for "low-end" glass or magnetics. For example, I simply do not need the ultra-fine resolution of them; my mill is small and I'm happy to work close to 1/20mm, nevermind 1/100mm. The only "features" I could use is the robustness, and in the case of magnetic scales, the possibility to cut them off anywhere.

Did you find some that are cheaper? If so, may I ask where you found them?

[philf]

Did you find some that are cheaper? If so, may I ask where you found them?

Hi Crazy Modder,

I don't know what country you're from but I guess in Europe if you are quoting Euros. Scales are certainly available in the UK for a lot less than 1000 Euro.

My whole lathe setup including the display and optical scales was less than £600 and they've come down in price since.

Machine-DRO in the UK do a range of optical and magnetic scales at reasonable prices. (Usual disclaimer.)

http://www.machine-dro.co.uk/digital-readout-systems-dro-pc-magnetic-glass-linear-scales.html?encoder_series=1138

There may be cheaper sources.

Cheers.

Phil.

[CrazyModder]

Thank you for that link. They indeed have a wide variety of scales, for example the GS10 series (0.005mm resolution glas scales) would be good enough for me. Those would cost just short of 400,- € for 3 of them. Or roughly 530€ for the cheapest magnetics. A far cry from the 1000€ I quoted, at least, while still more than twice as much as the mill itself.

I guess I'll get the cheap capacitor based scales first and if/when they fail, replace them with the more expensive and robust ones one by one.

[modeldozer]

Hi all,

Have researched the scales a bit and on the bay there are scales at around the 100 pound mark, other than that machine-DRO seems to be the best.  On the capacitive scales a 600mm one costs close to 60 pound so for me it will be glass scales on the mill.

Cheers
Abraham

[Arbalist]

Yes, Phil's link is for the supplier I was looking at. I was only going to go for X and Y axis to start to keep the price down. When I meant slight premium I meant over the optical ones. As well as being much more rugged the magnetics I looked at were also smaller which is a bonus.

Edit: I've just looked at the prices on that site and they've gone up a lot since I last looked!
Maybe I'll wait until the Chinese start making the Magnetic ones ... 

[BaronJ]

Ordered the MSP430 Launchpad from TI and developed a suitable PCB for the controller.  The PCB was made as universal as possible allowing for any scale voltage and internal or external clocking on each channel, selectable by jumpers.

Cheers
Abraham

Hi Abraham,

You have made a very good, neat job of the PCB and housing case for it.  I must admit it looks better than anything I could produce.  One question, where did you hide the MSP430 ?  I assume that the white module in the picture inside the case is the bluetooth one.

[modeldozer]

Hi Baron.

It is the long IC close to the regulators, it is removed from the valueline development board in order to save space, and yes, the white module is the bluetooth one.

Abraham

[BaronJ]

Hello Abraham,

Very clever    I wouldn't have thought of doing that.  It certainly makes for a very tidy layout in addition to keeping everything inside the housing where it is well protected.  It should help with suppressing any electrical noise as well.

Electrical noise is one problem that I have with the single scale on the mill.  It works fine for days and then when you need to rely on it the readout suddenly changes value or sometimes switches off completely.  Of course when it is switched back on it has reset to zero.  I keep meaning to get a properly screened cable for it. 

 

[Joules]

Baron,
         wrap it in tin foil till you get round to fixing it, or strip a length of coax, bunch the braid slide it over you cable and stretch it back out.  Good temporary fix   The turkey fat will keep the foil on your cable 

                 

[modeldozer]

Screening and supresion is one of the reasons I have used USB cables, ready made with connectors and decently priced.  You will also note in the schematic there are 3 different supply filtering capacitors for each scale plus the 100nf soldered directly accross the scale supply input.  My shop is full of electrical noise and so far the system is working perfecty.

Abraham

[BaronJ]

Baron,
         wrap it in tin foil till you get round to fixing it, or strip a length of coax, bunch the braid slide it over you cable and stretch it back out.  Good temporary fix   The turkey fat will keep the foil on your cable 

                 

Good Idea Joules
I've loads of old co-ax... 
Thanks:

[BaronJ]

Screening and suppression is one of the reasons I have used USB cables, ready made with connectors and decently priced.  You will also note in the schematic there are 3 different supply filtering capacitors for each scale plus the 100nf soldered directly across the scale supply input.  My shop is full of electrical noise and so far the system is working perfectly.

Abraham

Hi Abraham,
I had noticed that you seemed to have a lot of decoupling in there, and I can understand why.  In my case it seems that the mill motor is the culprit.  When the load on the motor rises the commutator sparks more and that seems to be when the readout fails.  The spindle speed display often plays up as well, which is not surprising since it is in the same box as the rest of the electronics.

PS.  Have you thought about making some PCB's for sale ?  I reckon that you have a winner there.

   

[modeldozer]

Hi Baron,

I will have to look into making the boards as my current setup is more geared to one of's.  The Eagle files are availeble to anyone interested in making the board.

Abraham.

[Arbalist]

My first Digital caliper was a Mitutoyo unit and when I bought a cheap caliper to leave in the workshop I noticed that it didn't immediately display the measurement in the same way as the Mitutoyo. In other words there is a slight delay between movement and display. Is this the same on the scales illustrated earlier and is it noticeable on your readout? If it were to the same degree as the cheap calipers I've bought I'd expect to either move the table on my mill more slowly or expect to have to "go back" after over shooting the mark so to speak.