[chbot] TTL to Line driver

FieldMate Precision grant at areameters.com
Mon Sep 21 10:39:23 BST 2020

Nice work Wallace!!


On 2020-09-21 21:28, Marshland Engineering wrote:
> Finally some time to reply. Something to read if you are bored.
> My trusted machine did a wobbly and started machining offset mid job. 
> Each
>  time it did this, I lost $400 in parts and 2 hours in down time. 
> Worked all
>  day once and and then skipped 2 mm the next. Very frustrating.
> The CNC machine has a South Western Controller made in the US. It is 
> about 35
>  years old but an exceptional machine. The position encoder is a wheel 
> that
>  runs on the table and its value is compared to the motor encoder to 
> check
>  tracking. The wheel encoder disk edge is radiused and the distance 
> movement
>  is calibrated by rotating the encoder on its axis. Not the kind of 
> thing you
>  can quickly buy from Aliexpress.
> Here is one.
> https://www.ebay.com/itm/Southwest-Industries-PRO-TRAK-M250-Digital-Metering-System-Head-M250B-M250C/184306441507
> Funnily enough, I did have a spare one of an earlier version I had 
> bought many
>  years ago from Ebay. On testing, it did not work. I opened it up and 
> it
>  looked very old technology inside. There was the finely graduated 
> rotating
>  disk and some odd looking components in it. It looked like there was 
> no power
>  going to the pickup circuit. There was rather a big blob of silicone 
> over the
>  one part. Grabbed it with a pair of pliers and yanked it off, only to 
> hear
>  the bulb hidden inside smash. This is an earlier version of a photo 
> pickup
>  with a BULB. I turned down a white LED changed the dropper resistor 
> and I had
>  light. I wish I had taken pictures of the 4 photo eyes. They looked 
> like
>  pinheads soldered to the PCB board. No bigger than 2mm in diameter.
> After recalibrating the resistors going to each of the eyes to get a 
> nice
>  clean signal, it was up and working.
> Whopedo. Unfortunately, the resolution was not the same as my original 
> ones.
> I contacted South Western Industries in the US and we went through a 
> few
>  steps. Needless to say, as the fault was intermittent, no fault was 
> found.
>  While chatting to the support chap, he mentioned 5 mew m, or something 
> like
>  that. Not quite sure what he meant, I questioned him on it.  Looks 
> like was
>  saying 5um.  Metric encoder on a US machine ???
> Luckily a few weeks before, I had bought a new DRO kit from Aliexpress 
> for my
>  bigger lathe. I normally use 1um linear scales however as this is a 1m 
> lathe,
>  1um is really small so I opted for a 5um set and saved some $$$.
> There we are, I needed a new 5um linear scale and I had it in stock. A 
> bit of
>  drilling and tapping and it was fitted. The TTL output however would 
> not
>  interface with the CNC control. I just piggybacked the output of the 
> scale
>  onto the encoder I had just repaired and away it went.
> I completed my job last Wednesday and shipped it off. Finally caught up 
> on the
>  back log of other work today.
> I think I may just make a small PCB for the TTL interface with the same 
> driver
>  ICS as in the encoder for the new scales. ICs are still for sale in 
> Mouser.
> Hope I haven't put you all to sleep.
> Cheers Wallace
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