Input signals for chinese DRO

This topic has 16 replies, 7 voices, and was last updated 19 May 2026 at 21:25 by Adam Harris.

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17 May 2026 at 17:59 #848637
Adam Harris
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@adamharris13683
I am embarking on a project to attach DRO’s to various machines and so far have a cheap generic chinese JCS900-3AE which is requesting an “R” signal wire from each of the linear scales, in addition to A,B, 0v and 5v. The problem is that I would like to use old Heidenhain linear scales (output incremental analogue signal) via a Heidenhain EXE interpolation/conversion box (output incremental TTL signal), and neither the scales nor the EXE box provide an “R” signal, so what will be the effect of leaving that connector pin empty, and what is that “R” signal anyway? Any help much appreciated.
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17 May 2026 at 18:03 #848640
Adam Harris
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@adamharris13683
The M-DRO BC-10 (a perhaps more popular chinese DRO) also asks for this 5th signal input from each linear scale, which in their case they call “Z”. Thanks in advance for any help
17 May 2026 at 18:10 #848641
Peter Cook 6
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@petercook6
My understanding is that the R signal is a Reference signal to provide an absolute position indication to the head unit. The idea being that if the scales have been moved while the unit is switched off traversing the scales past the Reference mark will get you back to an absolute position.

Magnetic scales provide this signal, as far as I know the optical ones – at least the cheap ones I have – don’t. I think the only implication of not having it is that you need to set your origin each time you power up the scales – or don’t move things when the power is off.

In a hobby environment, where the zero position shifts for each job that’s not usually an issue. In a production CNC setup it probably is.
17 May 2026 at 18:34 #848644
Adam Harris
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@adamharris13683
Hi Peter,

Many thanks for your quick response. So if I leave that connector pin empty then the DRO should work fine for me doing anything other than multi-unit production runs over several days?

Incidentally my old Heidenhain scales do have a distance-coded reference point every 20mm along the scale which i understood was for a similar purpose (maintaining an original refrerence point even when machine turned off and moved). The wire output from the scale reader head is 8 signals (Io+, Io-, I1+ I1-, I2+, I2-, 0v, +5v) and I have been told that “I1” = A and “I2″=B, so I think “I0” = Z (??), but the output from the Heidenhain analogue-to-digital conversion box EXE 829 drops the I0 (Z) altogether. Just outputs A+, A-, B+, B-, 0v .
17 May 2026 at 18:45 #848645
Adam Harris
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@adamharris13683
Should I assume an “R” signal is the same as a “Z” signal in Heidenhain terminology?
17 May 2026 at 18:47 #848646
DC31k
Participant
@dc31k
Even though you are not using it, the technical references on the TouchDRO site might help as the site has a lot of useful information on scale protocols.
17 May 2026 at 19:13 #848649
Adam Harris
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@adamharris13683
Thanks DC, that TouchDRO site is a useful resource especially its review of the quality and reliability of the different scales brands
17 May 2026 at 22:21 #848677
Dave Halford
Participant
@davehalford22513
Please note there is no standard for wiring pin outs for ‘generic’ Chinese DRO’s. There are at least 2 versions.

Older 1970’s Heidenhain scales use a incandescent bulb running at half voltage rather than an LED, don’t leave these powered up when not in use.
18 May 2026 at 08:55 #848737
IanT
Participant
@iant
The Touch DRO site is the place to go…

“A reference track is an additional signal channel (usually labeled Z, R, Reg, or Fiducial) that provides one or more precisely located markers along the length of the scale. After a power cycle, you move the axis past a reference mark, and the DRO uses it to restore the saved coordinate system. There are two common arrangements:

Periodic reference marks are spaced at regular intervals along the scale (typically every 50mm). After power-up, you only need to move the axis until it crosses the nearest mark — usually a short distance. This is the most common arrangement on Chinese glass scales from brands like Ditron, Aikron, and Sino. Some manufacturers also offer magnetic tape with periodic reference marks.

A single reference mark is placed at one specific location on the scale, usually near the middle or at one end. After power-up, you need to traverse that specific point, which may require moving the axis across a significant portion of its travel. High-end scales from Acu-Rite (SENC 150) typically come with a single reference mark, though other configurations are available on request.

Not all scales include a reference track. Many entry-level scales omit it to keep costs down. If automatic position recovery after power loss matters to you, make sure the scales you’re considering have reference marks.”

Regards,

IanT
18 May 2026 at 11:42 #848765
Adam Harris
Participant
@adamharris13683
Thanks Dave for that valuable tip. My reader heads are LS406 and LS303 both from the mid-90’s – I will check if they have LED’s or incandescent bulbs.
18 May 2026 at 12:02 #848766
Adam Harris
Participant
@adamharris13683
Thanks Ian for that extraction – very helpful. I have now also heard direct from M-DRO that while the Z (or R) signal gives this useful reference position info, the DRO position memory will work fine when the D-9 input connector pin for Z is left empty so long as the power is kept on for the session. Furthermore, in normal home workshop usage (ie NOT metres long axis travel on machines), if my scales are producing a differential TTL output of A+,A-, B+,B-, Z+, Z-, then it is perfectly OK to take take the A+,B+, Z+ signal wires and treat as A,B,Z for the D9 input pins, leaving the A-, B-, Z- signal wires blocked off. I had actually been told this by a Heidenhain agent but without him being 100% confident, so it is nice to see a DRO supplier say the same.
18 May 2026 at 17:16 #848800
Robert Atkinson 2
Participant
@robertatkinson2
Just to be clear, the need for differential signals is dependent on the the length of the cables not the length of the scales. Differential signals are less susceptable to noise and degredation than single ended. Cable effects are more more significant at higher frequencies so high speed or / and high resolution systems are more likely to use differential signals. Ideally you would use the differential signals and convert them to single ended at the display. A differential line receiver IC e.g. SN75175, with 4 channels, will do the conversion.

Robert.
19 May 2026 at 10:12 #848890
Adam Harris
Participant
@adamharris13683
Interesting Robert, thanks. Those SN75175 chips look cheap. Any source for the design of a circuit board? For dummies…
19 May 2026 at 12:07 #848894
peter1972
Participant
@peter1972
As your cable lengths are only about 1 metre, I very much doubt you need to use differential signals.

They would not manufacture digital readouts without differential inputs if differential inputs are usually necessary.

You could be wasting your time.
19 May 2026 at 14:15 #848920
Adam Harris
Participant
@adamharris13683
Thanks Peter – agreed so it won’t be going to the front of the queue, but I don’t mind wasting my time as it is a hobby after all.
19 May 2026 at 19:47 #848938
Robert Atkinson 2
Participant
@robertatkinson2
You hardly need a circuit board. Just a a bit of veroboard or half of one of these https://www.ebay.co.uk/itm/327089045021?

Apart from a 0.1uF capacitor across the supply pins you don’t need any other components. Even the capacitor is just good practice, not essential. It’s just differential input and single ended out. There are 4 converters per chip so enough for 2 encoders without reference output or 1.5 with. There are two enable inputs that just need to be connected to the 5V supply. The datasheet is here: https://www.ti.com/lit/ds/symlink/sn65175.pdf?ts=1779139760492 There are other similar chips with the same connections e.g. MC3486, any will do

Robert.
19 May 2026 at 21:25 #848956
Adam Harris
Participant
@adamharris13683
Thanks Robert
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