interface with bathroom scales - reading LCD infomation

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mark.duyvesteyn

Member
Im wanting to interface with a set of bathroom scales with a picaxe, so that i can log the weights and upload the data to a google spreadsheet.

I have a set of scales, that has four load cells, so reading the different strain gauges would be a bit tricky i think.

Is it possible to get the data by hooking up a picaxe to the LCD and reading that value directly? There are 16 lines to the LCD.


Cheers for any advice or help you can give me :)
 
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westaust55

Moderator
How about letting folks here know:

1, The make and model of scales with a link to the website
2. the schematic (what are the 16 lines you mention for)
3. which PICAXE are you hoping to interface to?
 
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Andrew Cowan

Senior Member
Can you show us a photo of the PCB and internal view of the LCD?

I'd imagine this is possible.

A

Edit - 'this' refers to interfacing with a PICAXE, not the photo.
 
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B

BeanieBots

Moderator
I doubt very much that you will be able to read the signals which go to the actual LCD part itself, (400Hz AC multiplexed signals) but it may well be possible to hack into the signals which feed the LCD driver.

A photo of the board would help a lot, however, if the circuit is not much more than a 'blob' on a PCB, then your only hope will be to interface to the load cells.
 
hippy

hippy

Ex-Staff (retired)
I was going to say as BeanieBots does, that it's probably not easy reading the LCD signals themselves. Not only are they likely multiplexed but probably high-speed analogue signals.

You would probably be better off taking a feed from the micro in the scales where it inputs the strain gauges, however, if the strain gauges are something more than a simple sensor giving an output that may not be achievable.

Hacking a system is fraught with difficulty; you really need to know what the circuit is, what voltages are used and how it operates. If none of that is publicly available you have to create it for yourself by reverse engineering and looking at signals on scopes. Sometimes one can make guesses which turn out right, other times they don't and can destroy the equipment.

One thing to remember is that many hacks only work with particular pieces of equipment and if that breaks and is not replaceable much of the effort put in may go to waste. You may have to start all-over again, hacking replacement equipment.
 
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papaof2

Senior Member
Possible alternative method?

Use digital camera or web camera (needs close-up capability) and capture the image. Transfer the image to a PC and use OCR software to conmvert the image to text. Upload the text.

Slightly longer process, but you may have all the pieces.

John
 
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boriz

Senior Member
Or use a more easily hackable scale. A mechanical scale would be cheap and easily hacked using an optical or magets+hall encoder.
 
hippy

hippy

Ex-Staff (retired)
@ lanternfish : Good link, and an especially good way suggested of getting round the LCD backplane voltages being analogue ( look for something to trigger on, everything else will be strobed sequentially ).

I can't tell exactly what sized pulses there are but seem to be in the region of milliseconds which should be within the capabilities of a faster PICAXE. It should also be possible to multi-sample so not absolutely necessary to read everything in one hit; wait for sync, delay Time1, read Data1, wait for sync, delay Time2, read Data2 etc.

Looks more feasible than I'd expected but I wouldn't want to try such a project without a scope.
 
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boriz

Senior Member
@lanternfish

"2012. Be afraid. Be very afraid (of the people who believe such nonsense) "

Are you talking about the olympics?
 
lbenson

lbenson

Senior Member
>2012

My guess: Dec 21, 2012, putative end of the Mayan "Great Cycle" calendar, and for some, the end of the world. Not much to do with bathroom scales, but if true, we may not need to worry so much about our weight. Eat hearty.
 
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lanternfish

Senior Member
lbenson said:
>2012

My guess: Dec 21, 2012, putative end of the Mayan "Great Cycle" calendar, and for some, the end of the world. Not much to do with bathroom scales, but if true, we may not need to worry so much about our weight. Eat hearty.
Click to expand...
Spot on. Some drivel we got talking about at work a week or so ago. And I have been eating hertily, too! And not because of the above. Got a dose of flu/bad cold and got laid low for a few days. And when I felt better I couldn't stop eating. Drove the wife nuts.

Reminder to self - check 'flu day' posts for incohetrent drivel and make apologies!;)
 
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