Start Simple With Low Cost Load Cell

I now have ambition to give my project machine’s work surface the ability to act as a weight/pressure sensitive scale. The first stop, as always, is Wikipedia which filled in the fundamental knowledge of a strain gauge load cell plus links to associated topics like the electronic design called Wheatstone bridge used to read the values of such contraptions. Seeking a little more detail, a web search found a page on All About Circuits that clarified a few fuzzy points.

With a basic understanding of what such a project would entail, I headed over to Amazon to see my load cell options (*). I knew industrial-grade precision load cells can sell for thousands of dollars, but electronic bathroom scales are sold for less than $20 USD. With such a wide range I wasn’t sure what to expect to see for a hobbyist friendly load cell kit. The answer: under $10 USD! (*)

This price is low enough I’m not tempted to try salvaging components from an electronic bathroom scale, I bought that kit and went to work. The advertised weight range up to 200 kilograms is an appropriate range for a bathroom scale. That is far more than I expect to (intentionally) put on my machine, but it is the cheapest option. I suspect the measurement granularity/precision would be pretty crude at the range I expect to encounter, but hey, it’s cheap and a good first step into this world of sensors.

Soldering the four strain gauges together into a Wheatstone bridge network wasn’t difficult, just tedious and involved a lot of double-checking to ensure I’ve connected the wires properly. But I was not able to verify the circuit with my multimeter. The strain gauge change resistance in response to load, but the change is far too small for my multimeter to pick up. All I could check is to verify I haven’t accidentally short circuited anything or left an open circuit somewhere.

So while I prefer to verify a circuit before powering it on, in this particular case I didn’t have the right tools to do so. The cheapest option is to proceed with hooking it up to the companion circuit board and hope for the best.

(*) Disclosure: As an Amazon Associate I earn from qualifying purchases.

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