John

Can you post pictures of the display, scales and connectors?

I have made a couple of Touch dro setups, so may be able to advise.

Stuart

John

As you say, those connectors are unusual for dro scales. I suppose no matter what you do, you will have to do some testing to identify the ground and 5v pins. The other two pins will be the A and B signal pins. If I understand correctly, these will be a square wave signal offset by 90degrees.

This is a link to a page on the TouchDRO website explaining the connections:

https://www.touchdro.com/resources/scales/glass/glass-scale-pinout.html

You should be able to make adaptors for a Ditron or other readout with this information.

I made my two TouchDRO adapters a few years ago using an Arduino on veroboard. For the first one, I used cheap digital calipers. For the second one I had bought some scales with individual readouts from Arceurotrade but found the display too small, so made an adapter to use TouchDRO and a very cheap Android tablet.

Looking at the TouchDRO website now, you can buy a ready built unit or diy kit or build your own from scratch.

I suppose it depends how much you want to spend!

Stuart

Has the bought unit been given a fair trial?    Feels like it’s being rejected for not having features that may not matter in practice.  A DRO that calculates PCDs is a convenience, but not essential unless lots of PCDs are drilled.  For occasional PCDs jobs, any CAD package will calculate the coordinates, there are online calculators, and it can be done with paper and pencil.  Likewise, mid-points are easily calculated.  What essential does the DRO not provide?

Wanting to replace a unit with “something more fancy”, is understandable, but may not be wise.  Up to you – if money is no object, replace everything – accurate scales matched to a high-end DRO that comes with bells and whistles, needed or not!  Buy the best of all possible DROs and be happy.  The alternatives suggested aren’t the best possible. they’re all more work and risky.  Mix and match, and TouchDRO is DIY.

Nor for me thanks.  Having plenty of other things to waste money on, I’d stick with the paid for DRO until it let me down.  To me a DRO is just another tool, all they’re chosen by balancing utility and cost to meet a need.  Though bells and whistles are fun, I explicitly avoid them – they’re more to learn and go wrong at extra cost.

But it’s a hobby so do as you like, whatever a miserable git like me thinks!

🙂

Dave

Having spent many years assembling and using electronic wiring, if the connector has only 4 pins it is because it needs only 4 pins: there are only 4 wires in the cable. Nothing wrong with “aircraft”-type rather than D-connectors, especially if genuinely to military or high-grade commercial quality. You’d need change them only to suit the replacement units. Why replace those anyway?

My milling-machine is a second-hand one too old to have been designed for DROs and the like, but I installed a 3-axis set by M-DRO, not something unknown from some Internet supermarket; and I am very happy with it.

The company knows our needs, and can supply what is right for the machine as well as user. I think I placed my order at the company’s stand at one of our exhibitions – certainly discussed it with the stand staff.

[Besides “our” suppliers deserve and need our support even if their goods are imported. Amazexpress and their ilk, don’t!]

It has many functions I have yet to use, including the halves. That can be overcome by setting the middle feature to (0, 0, 0) and read plus-so-far one way, minus-so-far the other, although that will lose any prior datum setting elsewhere on the work – often, a corner or a main axis. It also has PCD and arc calculator – oh, and calculator! – among various goodies I have yet to explore in the few years since I bought it.

Its only drawback is that switching between mm and inches (not within the same work!) seems to want the whole unit turning off and back on to register, which seems wrong – but that might be my fault. I may have missed something in the instruction-book! Which I have to say is very well written, in British English, not brave attempts without proof-reading.

.

Calculating pcd co-ordinates is not ever so hard though a bit laborious.

The Zeus books even include the appropriate factors. Or at least my editions do.

If you use ‘Excel’ or similar, create your own spreadsheet-calculator, using the diameter and hole-count as absolute-reference inputs. You could add further functions to give each hole’s co-ordinates from the primary datum on the work-piece.

CAD (2D or 3D) will let you plot a PCD anywhere on the item from its own centre, and obligingly gives that option of dimensioning everything from that primary datum.

As Dave says, be accustomed to what you have rather than what you think you want.

I think with careful planning you will find your apparently-basic DRO willl cover most of your milling, and the unusual rest by augmenting it with external help by calculator, spreadsheet, CAD or pencil-&-paper.

Let’s be honest – we are spoilt! A few decades ago we all had to count little marks on dials! (I still do, for small, simple operations.)

I bought one of these to replace a dead DRO, unfortunately the inputs are RS422 and my scales are I believe TTL. It is languishing in a cupboard until I can work out how to convert the output of my scales to 422.

This looks very promising:

https://thepihut.com/products/ttl-to-rs422-galvanic-isolated-converter?srsltid=AfmBOoq5bTJ8Wf9_0q_cfGk5NsS49y3rqBgUWueauORhMP3v7FCtyL93

MichaelG.

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Edit: __ More detail on the waveshare site

https://www.waveshare.com/wiki/TTL_TO_RS422_(B)

Thanks Michael, I’ve ordered a couple and I’ll give them a go. I’ll update the forum on the results.

On 1 September 2025 at 13:19 John Hinkley Said:

Referring to my post with the screenshots, the description does state ‘TTL’ for the connections, so I remain hopeful that my investment is just that.

John

 

I noted the same thing!

I’m 90% confident this is TTL, not RS-422.

Fingers crossed, sacrifice a virgin, wire it up correctly, and there’s a reasonable change it will ‘just work’.

What’s needed:

• Match the wiring from the scales to the head.  With luck the colour code used by the scales matches the colour code above.   If not some detective work is required, difficult without test equipment and a basic understanding of the electronics.
• Confirm the signal level voltages are compatible:  TTL is 0 to 5V.   Experiment by all means, just be aware that poking 5V into a 3.2V device, or 12V into a 5V is likely to kill them. I’m fairly sure the head is 5V TTL, not so sure about the sensors.
• If the DRO doesn’t fire up (in a good way) the next stage is to match the protocol.  The sensors send the head a stream of binary data that can be encoded in many different ways, transferred at any of several speeds, with or without error checks, and possibly intermixed with stop/start and other control signals.  Potentially complicated and both ends have to be correctly set in agreement for it work.  Thankfully there’s a simple common method, but no guarantee that’s what John has.  Early DROs and scales often implemented secret proprietary schemes.  Decrypting an unknown system isn’t for the the faint hearted, and it helps to own a logic analyser!  Likely to be too difficult for a beginner, even with expert advice.

Personally, I prefer to avoid such hassle by reading specifications before buying anything.  Guesswork is liable to be severely punished!   But let’s not start a gloom-fest – as I say it might “just work” – things are more standard than they used to be.

🙂

Dave

I suspect that Dave is being a little pessimistic in suggesting that there is any particularly complicated data protocol involved here. The sensor almost certainly just produces two quadrature pulse trains via the A and B channels, which is again almost certainly what the display head expects. And it doesn’t even matter which one is A and which one is B! The worst that would happen is that the DRO reads “backwards”, that is, the reading goes up when it should go down, and I would be surprised if there were not a setup option to correct this. It is important to get the 0V and +5V right, of course. The sensors I have played with (some glass, some magnetic strip) have just produced nominal 5V TTL pulse trains. I would even skip sacrificing the virgin and just rely on old-fashioned crossed fingers!

I stand corrected, the DRO I bought from aliexpress is not the same model, so it looks like I was unlucky that mine was not TTL. In mitigation I had no idea there were different interfaces available. At these prices I’m now tempted to just buy the right one rather than fiddle about with converters.

On 2 September 2025 at 21:28 Michael Gilligan Said:

To the best of my limited knowledge … the advantage of RS422 is that it’s reliable over long cable lengths

I doubt that’s of any great concern to you.

MichaelG.

 

That’s so.  The problem is that we don’t know what the designer had in mind, and he has plenty of choices. For example, RS422 vs TTL:

• RS422 is attractive because, in addition to long distance, it’s also fast with good immunity to electrical noise.  That might be considered important in a posh unit intended for reliable operation in a crowded industrial setting, and error correcting encoding might be added as belt and braces.
• TTL is cheaper, usually “good enough”, and many customers don’t need RS422’s extra features.

Therefore, a designer aiming at the economy market is well-advised to go with 5V TTL.  Except, keeping an eye on what’s available, he might notice a new chip is available that delivers RS422 for the same price.

There’s also a tendency to standardise, though it can take decades for a manufacturer to realise he’s losing business because his proprietary offering is incompatible with everyone else.  Might also force a design change.

Trouble is, what we buy is often poorly specified, making it tricky to be sure black boxes are compatible. Sometimes things connect easily, other times it’s a nightmare.  I blame salesmen!  Too many puff features whilst removing anything they don’t understand, especially important technical details!!!

Dave