Digital Read Out Problems

[Mosey]

I have 2 remote readers for cheap Chinese digital readouts Model #811-1 from Shars Tools. They both worked for a short time, then went dark. Replaced the batteries to no avail. There is no guarantee on them. Can they be fixed? or, do I just throw them in the garbage and move on.
I have since purchased the more current version and it works fine.

 

[portlandron]

Being that it's dead you have nothing to lose by trying to repair it. If it's anything other then bad connections parts would end up costing more, even if you could find them, then replacement unit.

Take it apart and check all solder connections and re-solder any that look bad. Also clean and check the battery connections.

 

[Tin Falcon]

Makes sense to me
Tin

 

[Mosey]

I took them apart, no bad joints to see, put in fresh quality batteries, and hooked them up to a new digital scale, and wow! they are working!
Now, it's back to the lathe to mount them up.
I tried this several times in the past and no success before. I wonder what I did differently this time? I still wouldn't recommend this brand. They seem to suck the batteries down even when Off??

 

[mzetati]

My (capacitive) scales stop working anytime I'm showering them with petroil: a few gentle blows of compressed air on the buttons and into the battery compartment bring them to life again.
Marcello

 

[Mosey]

Now, if I put the digital scale on the back of the lathe bed, I must turn it upside down, so that the zero is on the left (headstock) end of the lathe, right?, and the reading goes up as the carriage travels to the right (tailstock)?
Anyone do this?
Pictures ??

 

[kcmillin]

About the batteries.

Since batteries are for "Mobile" devices, is there any reason you can't hook up a power supply directly to the unit? Perhaps an old cell phone charger, or other transformer with the correct voltage and current?

Just a thought.

Kel

 

[JohnS]

Kel

One solution to replacing batteries with a direct power supply is featured here

http://start-model-engineering.co.uk/machines-and-tooling/milling-machines/battery-free-dro-display/

This option meets the requirement for dual power output - 3v to power the remote display and 1.5v to power the the vernier scale read-out head.

John-Som

 

[Mosey]

Terrific! I shall give it a try whilst trundling on. (couldn't resist).
Thanks from the colonies.

 

[Mosey]

Kel

One solution to replacing batteries with a direct power supply is featured here

http://start-model-engineering.co.uk/machines-and-tooling/milling-machines/battery-free-dro-display/

This option meets the requirement for dual power output - 3v to power the remote display and 1.5v to power the the vernier scale read-out head.

John-Som

Since our customary main voltage is 120vac, how would this circuit be modified?

 

[JohnS]

Mosey

I would imagine that it is simply a case of using a 120v ac/dc power adaptor in place of a 240v ac/dc adaptor - the aim is to deliver between 7v and 9v dc to the circuit. (if you use a power adaptor you omit the mains transformer and rectifier shown on the schematic on my web page).

Hope this helps

John-Som

 

[Mosey]

John-Som,
Do I take it correctly that by power adaptor, you mean one of those little 120vac to 6, 8, 9, or whatever vdc transformers that proliferate like rabbits, and serve screwdrivers, lamps, telephones, etc., etc.?

 

[Steelmaster]

I may be missing something, but why not use AA Lithium rechargeable batteries?

 

[Mosey]

No reason not to. It just seems as though these readouts eat them quickly, and then fail.

 

[JohnS]

Mine always seemed to fail without warning midway thro a milling operation which is the very reason why I wanted to dispense with batteries.

The weakest part of the whole DRO system on my mill is the read heads which despite protective covers do become contaminated with oil and fine chippings causing spurious readings. Again this usually starts to happen during a milling operation of repeat cuts. To overcome this problem I have fitted adjustable stops on X and Y travels. So I now set up using my DRO system for accuracy then lock the travel stops. A sort of belts and braces approach but it works for me.

Yes Mosey, the power adaptors are (to me anyway) like mini adjustable transformers that plug directly into the mains supply and offer a choice of outputs as you describe. Incidentally they do tend to put out a slightly higher voltage than suggested by the selector switch (say 9v rather than 7v as indicated on the selector switch) so check for actual voltage output with a multi meter.

In addition to the notes on my site a search on here will reveal a thread with further details and photographs which you may find helpful. Search for something like 'battery free DRO display'.

John-Som

 

[Ken I]

A lot of cheap verniers and DRO's don't actually turn off - they simply turn off the display. That power saving is negligable (LCD).

Try switching off - move the scale - turn on again - if the display has moved to the correct position - well then all the electronics (except the display) were working in the "off" position.

If it comes up zero then it probably was turned off - even then the on/off circuit is still active but that draws so little that the battery would probably go flat with or without it in the same timeframe.

I have verniers that do turn off and the batteries last ages - the ones that don't turn off chew batteries so I remove them when not in use.

2c Ken

 

[Drei]

When mounting the scales on the lathe always fix them upside down: the marked strip facing to the tray. This will avoid hot material chips from sticking into the scale strip, also when the chips are moved by the slider they wont damage the strip. That s what happened to me and some times the reading starts to freak out haha well i learned the lesson...

Drei

 

[mklotz]

Incidentally they do tend to put out a slightly higher voltage than suggested by the selector switch (say 9v rather than 7v as indicated on the selector switch) so check for actual voltage output with a multi meter.

My experience is that the voltage on many of these "wall warts" will drop significantly as soon as they see a load. If an exact voltage is required, check the voltage with a simulated load applied.

 

[Ken I]

Be very carefull of "Wall Warts" (cute Marv) they are usually very simple - transformer, rectifier & capacitor affairs - typically meant to charge batteries.

The output is not stable under varying loads and contains significant ripple.

Digital devices can be extremely fussy about the value & smoothness of their DC.

If you have ever tried to run a car radio / CD player (whatever) off a battery charger it generally won't work without the battery in the circuit as well - to flat line the DC.

 

[Blogwitch]

I have been using a battery eliminating power supply that John-Som graciously built for me over 2 years ago, and it works faultlessly on my mill quill scale, but the scale does need to have a capacitor in there across the +/-, definitely NO BATTERY, mainly to cancel out spurious electrical fluctuations caused by the machines motor. It's really nice not having to change batteries all the time, turn on, wait a few seconds for everything to stabilise and away you go. In fact I accidentally left the wall wart switched on for over two weeks while I wasn't getting in the shop, and it was still just sitting there, ready to go.

I played about with different values of capacitors until the fluctuations disappeared, and I think we both came up with the same figure, 0.22uf (a good starting point).


John