Electronic Weighing?

[tomlamonby]

Hi all

I'm toying with the idea of getting my 28 pin project board to weigh things, and fairly heavy things. I was wondering whether anybody thought it might be possible to hack an electronic bathroom scale, and somehow interface it with the board.. is this feasible? Using an existing bathroom scale would be much easier than trying to build that system..
I did a google search and a forum search but haven't found much interesting, I wonder if anybody has done something like this before? Any ideas?

Cheers

Tom

 

[QuIcK]

hmm, I had a look at howstuffworks. cant see anything about electronic bathrooms scales.
heres some ideas on truck weighing stations tho (same idea, just a different scale ... sorry, couldnt resist)
http://science.howstuffworks.com/question626.htm

looks like they work with strain gauges (which could be interfaced through an op-amp to the adc port)
or peizo-electric crystals (same, with op-amp -> adc)

I cant imagine it would be that difficult to hack one. even if its tying into lcd driver, either pre-driver so its binary or bcd or similar, or post-driver and using some sort of decoder chip.

another diy method would be to use capacitance. 2 rather stiff plates with a metal coating on each side held apart:

   Apply Weight
       \ /
        V
_______PLATE 1_____
-------------------
#                 #
#                 #
+++++++++++++++++++
_______PLATE 2_____

where --- and +++ are the metal coatings on the plates ___. And # are supports
wire plate1 and plate2 as the 2 poles of a capacitor to a timer-555 in astable mode. fiddle with resistor values, and it will give you a clock stream that relates to the capacitance on the scale, ie weight applied, which can be measured by the pulsin command.

 

[Andrew Cowan]

My 1kg max 0.1g accuracy sclaes (from china), use a strain gauge - a little box that produces an analogue voltage. Shouldn't be too hard to hack.

A

 

[spong]

Elektor had an article about this :

http://www.elektor.com/080027