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Load Cells ?

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Bluechip:
Has anyone hacked a set of el-cheapo digital bathroom type scales for the load cells ?
 
If so, what make ( preferably UK ).
 
Load cells often operate from 10VDC nominal, so what is the fiddle ( if any ) to get them on 3V from a coin cell which is the usual power source, or are they sourced from the 3VDC ?
 
Dave BC
 
 

awemawson:
Dave, I once tried and gave up!

I wanted to monitor the weight of a propane cylinder remotely as it was running my (inside) foundry with the cylinder outside. They all seem to work as a bridge. I ended up getting an industrial one complete with a panel mounting display, all mains operated (good old ebay!) but then moved house and never did install it - it's on the list !

The problem that I had was that all bathroom types I played with had an 'auto timeout' programmed internally so the display shut off after about a minute which was no good for my application.

Andrew

vtsteam:
Similar time out problem with a kitchen type digital scale I have for weighing out materials. It is mains powered but for some reason they retained the time-out feature as if it were battery powered. Very inconvenient as the period is short, and if you are trying to record something, load up gradually, or go get something else to add on the scale (say you're mixing ingredients) it shuts itself off.

If you had done a tare adjustment for the container, turning it back on doesn't help, unless you empty the container out again and re-adjust for it. Total pain in the neck.

I often switch to using my wife's spring scale, which never fails, is easy to adjust for tare with a slight twist of a knob (OMG analog controls -- how outre) and will patiently wait forever for you to do whatever you need to.

Unfortunately I got the new improved modern wonderfully accurate (at least according to the display) digital scale in order to avoid using my wife's kitchen scale. For easily understood reasons.  :doh:

Joules:
VT, the trick here is to have weighed the bowl and have a weight labelled up as the bowl.  Then when the bloody thing quit's on you, you can at least re tare for the bowl/whatever.   The only other solution here, is weigh near the white board and note everything down so you can add it all up later.  They weren't designed by engineers, or they would allow you to record offsets.

         Joules

awemawson:
If you're not looking for three decimal place accuracy you can make your own load cell. Bond a strain gauge to a beam of your choice with superglue and measure using a bridge circuit. Calibrate with known weights.

Andrew

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