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Glass scale /DRO compatibility

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Robin Graham12/04/2020 23:10:00
709 forum posts
167 photos

I have a Sino two axis DRO and one Sino glass scale , which I got (sort of) for free. The scale I have will fit on the Y axis on my mill, but I'd like to buy another for X.

I'm having trouble finding anything advertised as directly compatible with my DRO. All I've been able to find out so far is that the DRO inputs want TTL, but otherwise I have no idea.

This is the DRO:



Arc have some scales which would fit the bill price/size-wise , but they have 7-pin DIN connectors, so not plug and play. But maybe the same technology? I have a soldering iron!.

Any advice?


PS - when taking the pic of the readout unit I noticed that it has speaker output!  What does it say I wonder?



Edited By Robin Graham on 12/04/2020 23:15:24

Paul Lousick12/04/2020 23:31:04
1415 forum posts
541 photos

I have an Eason DRO with glass scales on my mill and they use a 9 pin plug as shown in your photo.


JasonB13/04/2020 06:54:08
18119 forum posts
1996 photos
1 articles

Quick look at M-DRO's website and their glass scales are TTL output and the same plug type, as they sold Sino and there current ones look to be own branded Sino that would be the safest bet.

Johnboy2513/04/2020 09:24:05
259 forum posts
3 photos

Most of the Linear DRO’s I’ve come across are a RS232 or RS485 industrial coms spec. I prepared be corrected on this though. 🙂

Compatible shouldn’t be a problem - it’s the pin outs on the connectors and/or connector types. With TTL logic levels they probably would be powered via +5 Volts..

If anybody else has any info or experience on this I would be please to hear. 👍

Dave S13/04/2020 09:39:28
40 forum posts

The Anilam readout on my CVA has DIN to D type conversion cables on it. IIRC the readout head have up on the previous owner, but the scales were ok and in the intervening years Anilam had changed over from one to the other.

This leads me to believe it is just a connector difference.


duncan webster13/04/2020 11:12:53
2591 forum posts
34 photos

According to this **LINK** M-Dro scales have RS422 output. They might well drive a unit expecting TTL, but if not a simple interface board would sort that out. More info on the Sino kit needed. The manual for the display is here **LINK**, but it doesn't give the required info

mgnbuk13/04/2020 11:35:28
766 forum posts
60 photos

M-Dro technical info sheet for SDS 6-2V here

Page 3 gives signal requirements & connnector pin-outs. Doesn't look to be anything special - A & B count channels, Z reference mark channel, 0V, 5V & screen connections

Nigel B.

John Hinkley13/04/2020 11:58:05
876 forum posts
293 photos


I've just been out to the workshop to check my Warco-supplied scales and DRO display fitted to the VMC mill. The scales output TTL (whatever that is) and the cables terminate with 9-pin D-plugs which would fit your DRO by the look of it. The Warco site is temporarily down at the moment, so I can't check prices/availabilty nor give you a link. They won't be that hard to find when the server is up and running again, though!


Edit:  Warco site OK now.  E.g.  400mm scale £100, delivered (to UK mainland)

Edited By John Hinkley on 13/04/2020 12:00:29

Pete Rimmer13/04/2020 12:08:10
716 forum posts
49 photos

TTL = transistor-transistor logic signal, for simplification purposes it just means square wave.

The unit you have is pretty much the common standard for budget scales and head units so any of the regular scales you'll find should fit it. You'd have a more difficult time finding new scales that didn't.

See if you can find the manual for the head unit because you might want to change the scale resolution setting. If you can't you better get a scale with the same resolution as the one you already have so that it reads correctly.


Nicholas Farr13/04/2020 12:11:08
2264 forum posts
1099 photos

Hi, TTL = Transistor-Transistor Logic. Which is the type of IC's used in the circuit.

Pete beat me.

Regards Nick.


Edited By Nicholas Farr on 13/04/2020 12:12:50

Nicholas Farr13/04/2020 12:25:04
2264 forum posts
1099 photos

Hi Robin, M-DRO, do a 7 pin to 9 pin adapter cable Adapter Cable scoll down to the third one, may be useable, I'm sure they would help you if you contacted them.

Regards Nick

SillyOldDuffer13/04/2020 13:32:26
5782 forum posts
1230 photos

Looks like the 9-pin D-connector is standard, but with two variants.

TTL means the logic is common as muck 5V rather than old school 80V, or 12V, and not super modern 3.2V

First variant of the D-plug is wired as shown in Nigel's example:


This is straight plain TTL. Note Pins 1, 3 and 5 are not connected.

The other variant is the same as above except it additionally uses Pins 1, 3 and 5 to carry the inverse of A, B and Z. Providing positive and negative versions of the same signal makes it possible to drive longer cables.


There's a good chance a display head will work with either convention, possibly automatically, but it may be necessary to explore the head's set-up menu to set one or the other. '232' means Pins 1,3 and 5 aren't used, '422' means all 9 pins must be operational.

A 422 only display won't work with a 232 only cable or scale, which is fixable as per Duncan's comment with a converter, but the other combinations should fly. It's worth just plugging it in to see what happens. The differences between scale, cable, and display are very unlikely to cause smoke!

Another problem might be making the display match the scales calibration. For example, the Z reference might fire every 50mm or every 100mm or some other value. Likewise the A/B steps (resolution) might be 0.01mm or 0.02, or whatever...

If the display works, but outputs the wrong measurements, check the display head's set-up menu to see what options it has: may well be possible to change them to match the scale.

Final point, beware of using ordinary RS-232 data cables. They use a different wiring convention, for example pins 2 and 3 are often crossed over.

However, the exam question is about ARC's 7 pin DIN connectors. Not enough wires to be EIA422! I think this is the manual for these scales.

It suggests this DIN 7 pin wiring:


So I'd chop the DIN plug off and rewire the scale to a 9 pin D-connector according to the M-DRO SDS6-2V table, first image above. I see ARC's site gives the Z reference point and grating pitch for their scales.

Black to pin 2
Blue to pin 6
Green to pin 8
Red to pin 7
Yellow to pin 9
Shield to pin 4



Edited By SillyOldDuffer on 13/04/2020 13:39:30

duncan webster13/04/2020 14:57:34
2591 forum posts
34 photos

So what does the Z pulse do?

Nick Hulme13/04/2020 20:35:35
743 forum posts
37 photos

Machine DRO (Allendale Electronics) sold Sino DROs, if you ask them I'm sure they will be able to help.

mgnbuk13/04/2020 20:54:18
766 forum posts
60 photos

So what does the Z pulse do?

Reference pulse. Depends on the scale maker - some have one pulse mid travel, others have a pulse near each end.

Used to regain a fixed datum after power off - if the axis is referenced before a datum is set, the same datum can be found after a power off by re-referenceing the axis.

On rotary encoders, the signal comes once per revolution. When used on a spindle encoder geared 1:1, it is the reference pulse that is used to synchronise the start of threads on CNC lathes.

Nigel B

Mike Poole13/04/2020 23:25:32
2575 forum posts
60 photos

The z marker can be used as a cross check to monitor lost pulses, incremental encoders are a problem on robots as unless you can remember the count when powered down and nobody moves the axis you need to reference the machine. A family of robots I worked on used a potentiometer that was geared to turn less than once in the full range of the axis. A calibration routine was performed where the robot driven to a mechanical datum then the each axis would drive to the Z marker for each turn of the motor and the pot voltage recorded, this would generate a file with a table of voltages for each turn of the encoder, once calibrated you could turn the robot off indefinitely but when power was restored the robot could quickly reference itself by driving to a Z marker and measuring the pot voltage comparison to the reference voltage file would tell the robot which turn of the motor it was on and so it knew exactly where it is. The downside of this calibration was that it could not always be performed in situ so the robot had to be removed to an open space. Of course this process had to be performed for each of the six axes. One of the problems with the servo motor was that the encoder had a mirrored glass disc that was mounted directly on the motor shaft so any play in the motor bearings would break or damage the encoder disc which meant replace the motor and recalibrate.

duncan webster13/04/2020 23:40:58
2591 forum posts
34 photos
Posted by mgnbuk on 13/04/2020 20:54:18:

So what does the Z pulse do?

Reference pulse. Depends on the scale maker - some have one pulse mid travel, others have a pulse near each end.

Used to regain a fixed datum after power off - if the axis is referenced before a datum is set, the same datum can be found after a power off by re-referenceing the axis.

On rotary encoders, the signal comes once per revolution. When used on a spindle encoder geared 1:1, it is the reference pulse that is used to synchronise the start of threads on CNC lathes.

Nigel B

Well you live and learn, I'll have to try to read the Chinglish manual again and see if I can make the display recognise it. Thanks

mgnbuk14/04/2020 11:49:05
766 forum posts
60 photos


I have a Jingce JCS900 dro - a manual can be found here

The "Ref" function is described from page 15. IIRC the Jingce scales have the reference marks 5mm from each end - if your scales are much longer than the machine travel, you may not get to cross the reference mark before you run out of machine travel. In this case the scale would have to be offset to one side to enable the reference mark to be crossed .


Not come across that way of working on CNC machine tools. Most control manufactures (except Fanuc) just use a mechanical switch to set a referencing direction then traverese to find the mark. Rotary encoders usually hit the switch, reverse direction & stop on the first pulse that comes along. Sticky switches or swarf can cause mis-referencing with rotary encoders. Scales with one pluse stop when the pulse is seen. Heidenhain scales sterted off with one pulse in the centre of travel on large body scales & one 10mm from each end on slimline scales. A later modification saw the large body scales get a mark every 50mm on the scale, with only one being enabled with a plate inside the scale body - a tool could be used to set the active mark. Later still they came up with "Distance coded" marker pulses - nominally on a 20mm spacing, the actual spacings between marks vary by a few microns on a known pattern. Passing over two adjacent marks, counting the distance between them & then comparing to a "map" in the control software allows the position on the scale to be calculated - saves a lot of time referencing large machines compared to travelling each axis to one end of travel.

Fanuc do their own thing - they use a "reference counter" that is started when the first mark is seen. This counter is set to the pitch of the ballscrew (in microns) in parameters & increments or decrements from the count pulses. When the counter equals the parameter value, it outputs a virtual pulse & this (in conjunction with a switch) is used to reference the machine. Thye also offer "Absolute pulse coders" - which are not absolute at all. These encoders have a battery backed counter built in. The encoder is kept active by the batteries & updates the counter if the axis is moved when machine power is off. When the machine is turned on again, the counter values are read by the control & operation resumes without referencing. If the batteries fail, the machine references as normal.

Not come across glass encoder discs breaking in normal operation, though understand that CNC punch presses contiunued to use resolvers rather than encoders, as resolvers are more robust in that continuously pulsing environment.

Nigel B.

Robin Graham14/04/2020 19:49:14
709 forum posts
167 photos

Thanks to all for replies.

I am reluctant to ask m-dro for advice as I'd then feel obliged to buy from them.

From what's been said it looks like the Arc scales should work with the Sino DRO - it's just a matter of mapping the connections from the DIN plug to the D-type, and Dave (SoD) has given pin-out for the DRO and (likely) pin-out for the scales - thanks for that research Dave. So out with the soldering iron!

I have the same DRO on my lathe (it came with it fitted, but no manual), which is why I have a spare. Axminster replaced the faulty one (and the apparently faulty cross slide scale) under warranty, but weren't interested in taking back the originals. Turned out it was just the PSU in the readout (fixed for under a tenner), and an alignment problem with the scale. It would be a shame not to get this stuff working on the mill where it would be more useful than on the lathe. Looking at the manual Duncan gave a link to, the readout can do all sorts of wonderful calculations.


Nick Hulme15/04/2020 20:14:11
743 forum posts
37 photos

Machine DRO sell adapter cables

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