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I have a project in mind where I want to measure the weight and position of an item on a shelf. The idea was to mount the shelf on a load cell in each end and then get the weight and ratio between them to get the position. At the time I was wondering what is the cheapest way of getting electronics to measure the load and transmit it via Bluetooth to a phone. I ended up buying the Pi Zero W, because of the price (and that I love Raspberry Pi and have used them with wifi dongle previously), but its been years since I've used them and I didn't research if its possible to use it for my purpose. Can I connect 2x or 4x load cells to my Pi Zero W and be able to individually read the applied load on each load cell? I guess I can use 4x of my HX711, but what pins can I connect them to?

Let me know If my approach is wrong and some other electronics is better/more reliable.

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The overall series of questions is too broad for this site.

Generally we expect one question.

I will comment on the load cell ADC (HX711). I doubt that you can usefully interface more than one to a Pi at a time. They normally expect a continuous chain of pulses to clock the returned data. If a pulse stays high for more than 60µs the HX711 enters power down mode. I'm not aware of any software which handles that situation properly for more than one HX711 on the Pi.

  • Sorry about that, but thanks for replying. I'll try and make a prototype out of some smaller load cells I have and report back/refine my initial question. – user1171426 Sep 19 '18 at 12:00
  • No problem. You might get a more useful response to a broad question at raspberrypi.org/forums It's just that the Stack Exchanges are more geared to Questions and Answers. It's not always an obvious distinction. – joan Sep 19 '18 at 12:12
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"I guess I can use 4x of my HX711, but what pins can I connect them to?" Answer - any GPIO pins.

For tech info consult the data sheet. Here https://www.mouser.com/ds/2/813/hx711_english-1022875.pdf As already pointed out the interface is digital but proprietary. But the format is well documented. The catch is - the output is triggered by time events, so you will have to consider that even in single device prototype.
Using more than one device, multiplexing, will require more design time.

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The way 4 load cells are handled in one item for production quality large-scale is to get four load cells, then on a board add their signals together with one cumulative output of the analog signals. It will by default take into account the addition of all 4 sensors. The one output cable can then be hooked up to an HX711 with great result on the end.

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