# Battery free DRO display



## JohnS (Jul 15, 2008)

Some of you may recall my earlier post when I was trying to find a method of running the x and y remote display units from mains electricity rather than the two 1.5V batteries for which the units are designed to take. The essence of the problem is that you need both 3V to power the display and 1.5V to power the sensor.

I had a most helpful response from Peter in Australia and Sandy in Scotland. Peter was up to his neck with work so Sandy kindly undertook to design a circuit, which would do the job.

The outcome has been most successful and Sandy felt there may be other members who may like to put one of these devices together. 

The DRO X and Y DRO displays on my mill now powered by my new dual output regulated supply.







Whilst the circuit schematic, as supplied by Sandy, gives full details of the necessary mains transformer and AC/DC rectification components, the good news is that you can avoid having to play around with the dangers of mains electricity by using a readily available cheapo AC/DC power adaptor. (As used to run radios or cameras etc. from the mains supply) having either a fixed, or adjustable DC voltage output.

Warning - I would at this stage like to make it clear that neither Sandy or I, can accept any responsibility for personal injury or damage to equipment should you decide to construct one of these units. 

From a performance point of view the only minor downside is that, when you switch off, the reading isnt retained in the displays memory.

One final word of caution to anyone using these remote DRO display units, regardless of whether you are using batteries or mains derived power supply, it is important to remove the small cell battery in the scale sensor unit. I didnt appreciate the need to do this and as a result battery leakage damaged one of my sensor units.

Should anyone like a copy of Sandys schematic diagram, build notes and a list of components send me your email address via a pm on the site and I will send these on to you.

I purchased all my components from Maplins at a cost of around £20 (approx $40 US dollars). Adjustable voltage AC/DC power adaptors are readily available and I found a couple in original packaging at just £4.00 each at a local car boot.

I found that copper stripboard was ideal for the build. All the components were slotted loosely into position before soldering on the reverse side.





I used a crocodile clip as a heat sink.






Here are one or two pics of the completed dual voltage regulator unit with adjustable AC/DC power adaptor.

Min-din plugs and chassis sockets provide neat connections from unit to DRO displays. The final connection using choc-bloc connectors which slip conveniently into the battery compartment in the DRO. 






I would like to thank Sandy for designing this useful unit and for his patience in guiding me thro the build of the prototype - thanks Sandy.

John S


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## CrewCab (Jul 15, 2008)

Very neat John :bow:

Just a thought, is it possible to incorporate a battery back up in the circuit, similar to a computer which stores time and date, just so the reading isn't lost when you turn off?

Dave


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## JohnS (Jul 15, 2008)

Thanks Dave

It is possible to switch off the DRO and providing you don't turn off the AC/DC power adaptor the readings *are* retained but I would not be too keen on leaving the power adaptor switched on overnight.

John S


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## Divided He ad (Jul 15, 2008)

Sign me up John.... I have the same DRO's as you and find the power failings very annoying.

I have my £20 ready so await your P.M. or E-mither ;D 



Ralph.


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## CrewCab (Jul 15, 2008)

Thanks for the info John, and, just to be nosey : .............. as I see your mill is the same as mine ............. what DRO are you using for X and Y .............. and Z 

Cheers

CC


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## JohnS (Jul 15, 2008)

Hi Dave

Here's a couple of pics of the x and y digital scales which are simply basic cheapo scales costing less than a tenner each. The same goes for the z reading. 










John S


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## CrewCab (Jul 15, 2008)

Thanks John,

Are they digital callipers with the jaws cut off or can you buy just the scales, the one's I've seen are considerably more ............. for instance........... *These*
 and yet another question, what about the display 

Sorry for all the questions, I've obviously been hanging out with Ralph too much :big: ;D :big:

Dave


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## JohnS (Jul 15, 2008)

Hi Dave

Yes they are digital calipers with the jaws cut off - used a mini angle grinder, the steel is as tough as old boots ! The displays are from Arc Euro Trade http://www.arceurotrade.co.uk/Catalogue/Measurement scroll down the page and you will find them at £30 each. I reckon I bought all three scales and the two displays for just under £100 and was worth every penny in terms of accuracy and ease of use. I keep meaning to set up something similar for my lathe but to date haven't got round to it. 

John S


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## CrewCab (Jul 15, 2008)

Thank you John, DRO for under £100 seems very appealing certainly more within my budget anyway  ............ if I'm not mistaken John from ARC Eurotrade is on this board, perhaps he could consider selling pre cut callipers : .......... just a thought :big:

Anyway many thanks for the help, looks like my to "do list" just got longer ........... 

Cheers

Dave


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## Loose nut (Jul 15, 2008)

Did you say each scale uses two 1.5 volt batteries, mine look the same but only use one each.


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## JohnS (Jul 16, 2008)

Sorry LN if I confused you (or anyone else !) The voltage regulator has been built to provide a 3V and 1.5V supply to both the X and Y DRO display units. 

In both cases the 1.5V supply is fed back to power the scale. You are quite correct in that there is only one 1.5V cell battery in each scale and it is important to remove this 1.5V cell battery from the scale when using the remote display units regardless of whether you are using batteries or the voltage regulator.

Sandy has explained further the difficulty in retaining data in the DRO display and, I quote "The biggest problem would be to separate the charging and discharging paths for the battery such that neither effected the other.... and switchover timing would also be quite critical if data was not to be lost...... possible yes, but not so easy as it first would appear to be"

John S


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