avoinvents said:
Do you think that a mat could be made as sensitive as a barometer?
My idea is designing a inflatable mat that could determine weight of say 10grams placed on it and display an accurate reading of the weight shown on a LCD panel.
Many thanks for your help in advance.
Many times in product design, you need to look at the overall thing you want to do, and consider how to optimize the accuracy and sensitivity and cost and whatever else is important, subject to the constraints you have for the design. As an engineer, you should always be striving to optimize your designs in whatever ways are important. To come up with a sub-optimum design is generally a bad thing. You have the computational tools, generally, to calculate things through, so doing lots of thought experiments and paper designs is part of what we do...
So in this project, you need to ask yourself what the accuracy constraints and concerns would be with using an inflatable mat to measure weight via pressure changes. What is the pressure change inside your mat for a 10g weight being added on top of the mat? What kind of accuracy, resolution, and pressure ranges are available with off-the-shelf pressure transducers that you might use in your project? What kind of preamp would be appropriate, and what would you expect your signal-to-noise ratio (SNR) to be with that 10g weight that you are trying to measure?
Now think of other ways to do the same weighing funtion. How do the various types of bathroom scales work? They are not optimized for small weights, however. But you should at least calculate what the SNR is for light weights for your inflatable scale versus some other options, like a 4-footed rigid platform, with strain gauges at each of the feet (or 3 feet might be better, if you loads allow -- Quiz Question -- why would 3 feet give you a better SNR than 4?).
If you are measuring only light weights of a limited weight and size, then maybe something more like a spring balance mechanism, with one spring, one hinge, and an optical encoder for displacement might be better still...
Think about what you really want to do, and then spend some time calculating through the various transducer and measurement options. Try to be as quantitative as possible, with an end goal of something like bst SNR versus size/cost/convenience, etc.