Digital Read Out Displays

[JohnS]

Having fitted Digital Read Outs with remote display units to my Chester Conquest Mill the passage of time has thrown up an irritating problem. The four pin plugs that fit into the scales have proved to be very insecure. On more than one occasion the signal to the display has disappeared in the middle of a tricky machining operation leaving me at sea without a rudder, so to speak. Does anyone have a solution to this problem ? I am tempted to superglue them in position but suspect I may live to regret such drastic action – though I cant think why !

My second question is posed in the hope that there may be an electronics expert in our midst. I have also found that batteries in the remote displays can expire without notice – and again this always happens at a most inopportune time. One suggestion is to ditch the batteries and use a small variable transformer. On investigation there are two power leads in each unit – one drawing 3 volts and the other 1.5 volts (the second 1.5 volt supply takes current back to the scale sensor). I have got as far as wiring the two units in series from a 6volt supply giving the required 3 volts to each unit but am at a loss as to providing the 1.5 volt supply in each unit. Any ideas anyone ?

John S

 

[Classic]

John, my main area of expertise is electronics, and I'll help if I can, but I haven't any experience with these DROs.

I'd suggest hot melt glue instead of super glue to hold the plugs in.

As for your second question, I wouldn't recommend connecting the units in series because of the possibility of the units creating electrical noise and interfering with other. The other danger in this method of connection is that a failure in one unit could cause the whole 6V to be applied to the other unit, possibly damaging both. A 3V regulated supply should be available. I know for sure that they are available here.

Can you give me a link to some information about the DRO? How many, and what type of batteries do they use? You may not have to use two separate supplies.

Alternatively, maybe someone else has already done this and can tell you how.

Peter.

 

[Divided He ad]

Hi John,

Just a quick note, My DRO's do the same on my Chester Champion, They have been done with a glue gun... Super glue could cause all sorts of trouble!

not too sure about an external supply ? But there is something I haven't investigated properly yet, the small cell battery is not required on mine most of the time? The power from the head display seems to be enough. Then once one stopped working all together and I put a button cell in and it all started working again?? ??? :-\

As I said I've not put much thought back into it... Maybe I'll have a go?!

Good luck!


Ralph.

 

[JohnS]

Thanks Guys

In answer to your question Peter the units are powered by two 1.5V AAA batteries. I have sent you a pic of the unit by email as I still haven't mastered the black art of sending pics on here - hope thats OK !!! The hot glue suggestion has popped up three times now so thats the route I will take in terms of securing the cable connection into the scales.

JohnS

 

[Classic]

For the benefit of anyone else watching this thread, it seems that the Digital display is supplying 1.5V to the scale unit by tapping from one of the 2 batteries. There is usually, therefore, no need to have a button battery in the scale unit, unless something fails in the connection between the readout and the scale. If you have a button cell in the scale and it goes faulty, it will quickly flatten one of the batteries in the readout.

This method of supplying half the battery voltage is not recommended, because, even under best conditions, it will flatten one of the readout batteries before the other. It's not difficult to come up with a 3V and 1.5V regulator that will power the whole shebang from a plugpack/wall wart, so batteries can be forgotten. If there's enough interest, I'll try to come up with something, but it will take a month or so, because I have a current backlog of about 50 guitar pedal orders.

Peter.

 

[JohnS]

Hi again Peter

As you know I have sent you further info via email as I am unable to add pictures to my posts on here. The info you have provided to date is most helpful and I would like to take up your kind offer and will happily wait a while longer to go battery free.

JohnS

 

[SandyC]

;D

Hi Guys,

I agree with Peter on this one, an external power supply is what is required.

A very usefull series of low voltage, low drop out, regulators are made by Advanced Monolithic Sytems Inc.
One of which is admirably suited to the above task.... AMS2954CP-X.

This is available as an 8pin dip package and can be used either as a fixed voltage regulator (can be easily pin strapped for 3 volts) or can be used as an adjustable regulator (range 1.24v - 29v)

Input voltage can be up to 30v.

A small transformer, bridge rectifier, smoothing capacitor, a pair of these devices and a couple of resistors and decoupling capacitors will give what is required.
The whole thing can be built into a small box of similar size to one of the DRO readouts.

I attach a full data sheet for these devices.

Hope this is of some help.

Best regards.

SandyC GM8ICC ;D ;D


View attachment ds2954 voltage regulators for DRO supplies.pdf

 

[Bogstandard]

Sandy,

Great post, dead easy to understand, so that is black wire to red doodah and blue whatsit to red wire.

As you can guess, wiggly amps and electric string isn't my forte.

I can just about understand a basic circuit diagram.

Damn, it must be real nice to have brains.

John

 

[Classic]

Thanks for jumping in Sandy. I was thinking of a small charge pump regulator, but I guess ultimate efficiency isn't a big deal in this case.

If we can come up with something that's easy to put together, many members should be able to assemble it themselves. I'm not looking to make money out of this - just trying to repay for all the things I'm learning here. It's such a simple thing that it could probably be done without a custom printed circuit board.

Damn, it must be real nice to have brains.

John

John, you've gotta be kidding. I wish I could muster up a small fraction of your creative engineering and organisational skills, not to mention sense of humour ;D

Peter.

 

[JohnS]

Thanks guys for all the input - I am OK so far on using the glue gun to hold the plugs in place on the scales - that much I can do, in fact I've done it and the connections are nice and secure.

Now when it comes to electrics I am ok wiring up a simple circuit, what I don't know is which bits to put in and in what order. I suppose what I was hoping for was someone to come up with a Bogstandard type diagram using a few bits and pieces out of the kitchen drawer and maybe some techy components from Maplins (UK electronics store). Life is never that simple, however Peter has kindly offered to put something together and this gesture from the other side of the world is much appreciated.

JohnS

It was a week ago today that I had the pleasure and privilege to spend an educational day with Bogstandard - and boy did I learn !
I can now set up my vice properly on the mill table - I didn't even know I was doing it wrong in the first place - now its dead square and level. Same goes for the rotary table I was doing it all wrong and thinking back its amazing I made anything at all that actually worked. Now I can experience the joy of holes appearing in the correct place and components fitting neatly together - I've still got a long, long way to go but at least, thanks to John, I feel as though I am getting the basic foundations right. He hates me to thank him but I am doing so publicly anyway ! Thanks John.

 

[SandyC]

Hey BOGS....what red doodah?..... I thought it was green ;D ;D

John S

If it is not stepping on Peters toes, seeing as he has already offered,  then give me a few days and I will see what I can sort out for you..... I am in the UK so will use readily available (uk) components. (either Maplin or RS probably)

As for the black wire connects to this and the big blue thingy connects like this...I will also see what I can do on that score.....who knows...even Bogs might try his luck.

I was thinking of a circuit that could be used on both sides of the pond so will try to stick to components available on both sides.

Let me know if this would help, IF so, then it would be helpfull to have the data sheets for the readout and scales.
PM me your e-mail address and we can contact off site.

Keep happy.

Best regards.

SandyC  ;D ;D

 

[GailInNM]

How about using a simple brute force sledgehammer approach of putting a pair of AAA consumer grade nicads in each unit and use a 6 volt (or so) wall wart charger with a dropping resistor to keep them charged. The charge current can be a very low trickle rate as the DRO's don't use much power. Then even if you have a power failure or even turn the power off for a month while on holiday the DRO will still keep it's reading. If you shop a little, the 300 mAh AAA nicads are only about a US$1.00 each and you probably have a suitable wall wart power supply laying around. The nicads will act as both a voltage regulator and filter for the wall wart.

Gail in NM, USA

 

[SandyC]

Hi Gail,

On the surface this looks like a great idea, however, there are several reasons it would not be suitable.

1.  Nicad cells, or NiMH cells are only 1.2v each, therefore only 2.4v would be possible...wherease 2 x Alkaline AAA cells would be 3 volts.

2. Both Nicad and NiMH require charging with a constant current, typically for constant trickle this would be 1/50 of the normal capacity.
This would mean around 6mA for 300mA hr batteries.

3. The batteries are in series in the display and one is also tapped off to feed the sensors, thus one battery has a different discharge rate to the other, and therefore each would require a different charge current in order to satisfy both the charge and load currents at the same time otherwise you would result in an imbalanced charge pattern. You cannot do this with series batteries.

4. A simple wall wart charger with a dropping resistor could not perform such a task.

5. Nicad chargers are very dirty (noise wise), they are constant current devices and have a variable voltage output, and to try and use one whilst also driving an LCD display and/or sensors would result in a great degree of instability in the sensors and the display would most likely be unstable and unreadable.

Sorry to dash your idea but Physics is Physics.

Keep happy.

Best regards.

SandyC ;D

PS...John S I have received your PM and will e-mail you in the morning once I have got my thought into order.

 

[Classic]

Sandy, I'm pretty busy for the next month or so, so, if you have more time, please go ahead. I agree with your comments about rechargeable batteries. It surprises me that any manufacturer would stoop to tapping one battery to obtain 1.5V for the sensors.

John S tells me that he is measuring a load of around 250mA, which concerns me, because it seems way too high and may explain why his batteries are failing in the middle of jobs. I expected less than a tenth of that.

I've searched high and low for data sheets for the readout and drew a blank. I found the pin connections for the 4 pin connector on the scale/sensor by googling digital caliper interface, but haven't found any other data. The button cell in my verniers is definitely 1.5V and is connected directly to the two outer pins of the interface.

Component availability is no big deal. If I need small quantities of components and can't get them in a local electronics store, Farnell's prices here have dropped to reasonable, and otherwise it takes no more than a week to get components from Digi-Key, Mouser etc in the US.

It may be worth considering fixed regulators, to make it easy for guys with limited electronics experience to DIY. There are now a lot of small low voltage regs available.

Peter.

 

[SandyC]

Hi Peter,

Thanks for your agreement, I though it would be easier since I am in the UK, but did not wan't to upset anyone.

I have now furnished John with a suitable circuit and he is going to have a go at building it..... he will keep everyone informed of progress.

I ended up choosing to use floating regulators (LM317T) which are much more readily available on both sides of the pond, and a tried and tested device.

Yes the cells in your verniers would be silver oxide type which are 1.5v....these should, of coarse, be removed if powering from an external source, since they don't take kindly to an external current source....they are not re-chargeable and can burst under such conditions...MESSY.
Most guy's fit a small SM (surface mount) or tantalum bead capacitor in the battery box when externally powered, to ensure low noise.

This can be a bit tricky, due to restricted space but take a look at this site: -

http://www.robotroom.com/CaliperCapacitor.html

Best regards.

SandyC ;D ;D

 

[Circlip]

Hardly dared to suggest 317's Sandy in todays Hi tech, saw some SM adjustable regulators on Farnell lists, but no data sheet.

Regards Ian.

 

[Classic]

Sandy, I think you'd be surprised how many components are available here, but yes, the LM317 is a good choice that is common and easy to get.

I finally uploaded an avatar. It's a PCB from one of my products and is a mix of SMT and through-hole technology. I hand solder the lead-free boards for your neck of the woods, but for the non RoHS boards, I use lead-tin solder paste and a hand held vacuum pick&place tool that I made. I then reflow solder them in a small combined infra-red and hot air reflow oven that I also made. The smallest SMDs I've hand placed and soldered so far have been 0603 size, 1.6x0.8mm. I find SMT easier and quicker to work with for design and prototyping on veroboard (strip board).

The regulator on that board is a charge pump switching regulator. I didn't use the surface mount version because it is 14 pin and actually uses more board space than the DIP8 version.