I asked a similar question in the raspbi forum and they sent me here.
I have a table (15kg) at the office where routinely packets with weights that range from 40-100kg are placed.
I would like to see when a packet is ready for processing and store the traffic in a database using a raspberry pi or other computer.
Now I have tried a few load cells I could get my hands on, like the fx1901 or a couple strain gauges, but they seam to stop working with large weights or not even work at all.
I also saw there are flat paper like force resistors, which would be absolutely perfect, since I could just put one under one of the table legs, but they only seam to 10kg, and I need at least 100kg.
So does anybody of you know of a way to detect large shifts in weight (15->55+)kg that doesn't have to be accurate, I just need to know that it happened, that I could wire up to a raspberry or equivalent HAT that would allow me to track the packets on that table?
Or can you think of a different solution to my problem?
Just to summarize, theres a table (15kg) on which packets (40-100)kg are placed, and I need to track that happening, perferably with a raspberry pi.

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put on hold as off-topic by John Rennie, Chair, Kyle Kanos, ZeroTheHero, rob Dec 9 at 0:39

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  • 3
    This is really an engineering question rather than a physics question. For what it's worth my approach would be to use load cells under the legs. I can't see why this wouldn't work. Maybe you just need better quality load cells. – John Rennie Dec 8 at 11:26
  • I found some online but they cost 200+$. Also they are pretty big making the table uneven. I was hoping since I dont need acurate measurements thered be a cheaper solution – user1510024 Dec 8 at 12:04

Get you an old style analog bathroom scale with a rotating display disc that has the weight numbers printed on it. Hack the scale open and punch a hole through the weight marking at which you wish the signal to be triggered. Straddle the disc with an optodetector pair so that when the disc indicates the desired weight, the light beam goes through the hole to trip the detector. Wire the detector to the raspberry pi.

  • Thanks for the suggestion, this might be a good solution if I can't find an propriate force sensor. – user1510024 Dec 9 at 8:12

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